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Article

Consecutive Multicomponent Coupling-Addition Synthesis and Chromophore Characteristics of Cyclohexene-Embedded Merocyanines and Cyanines

by
Julian Papadopoulos
1,
Tabea Gerlach
1,
Guido J. Reiss
2,
Bernhard Mayer
1 and
Thomas J. J. Müller
1,*
1
Institut für Organische Chemie und Makromolekulare Chemie, Heinrich-Heine-Universität Düsseldorf, Universitätsstraße 1, D-40225 Düsseldorf, Germany
2
Institut für Anorganische Chemie und Strukturchemie, Heinrich-Heine-Universität Düsseldorf, Universitätsstraße 1, D-40225 Düsseldorf, Germany
*
Author to whom correspondence should be addressed.
Photochem 2022, 2(3), 672-693; https://doi.org/10.3390/photochem2030044
Submission received: 14 July 2022 / Revised: 15 August 2022 / Accepted: 16 August 2022 / Published: 19 August 2022
(This article belongs to the Special Issue A Themed Issue in Honor of Professor David I. Schuster's Great Contribution)
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Versions Notes

Abstract

:
Merocyanines with embedded butadiene structure in a cyclohexane scaffold are readily obtained by consecutive three-component alkynylation-addition sequences in moderate to excellent yield. Moreover, employing pyrrolidine as an amine provides a pseudo four-component synthesis of related cyanines by carbonyl condensation of the heterocyclic amine in excellent yield. While the merocyanines are essentially nonluminescent, pentamethine cyanines show luminescence with low quantum yield. TDDFT calculations using various exchange correlation hybrid functionals in the gas phase and explicit continuum of dichloromethane underline that the lowest energy absorption bands are highly solvent dependent for a merocyanine and cyanine model. The blue-shifted deviation from the experimental spectra agrees with related merocyanine and cyanine systems. The lowest energy absorption band of merocyanines contains n-π* character, which rationalizes the absence of luminescence.

1. Introduction

Merocyanines [1,2,3,4,5,6] are structurally characterized as neutral polymethines possessing high extinction coefficients and as highly polarizable π-electron systems. This sets the stage for applications in optoelectronics [7,8,9,10], organic semiconductors [11], and photovoltaics [12]. Due to their polar nature and polarizability, their self-assembly in solution enables access to nanoscale objects and supramolecular materials [13,14]. Classical synthetic approaches to merocyanines and many polymethine dyes are conventional aldol or Knoevenagel condensations [1,15,16,17]. More modern concepts for the synthesis of functional chromophores, such as fluorophores and electrophores [18,19,20] with heterocyclic scaffolds rely on multicomponent reactions (MCR) [21,22,23,24] and domino processes [25,26]. In particular, generating alkynoyl intermediates as part of the catalytic entry to MCR [27] paved the way to several fluorophores in a modular one-pot fashion [28]. In recent years, we have reported concise consecutive three-component syntheses of luminescent merocyanine luminophores based upon an alkynylation-addition sequence [29,30]. Upon derivatization, the merocyanines could also be embedded as covalently bound constituents in highly fluorescent PMMA copolymers [31]. Encouraged by the three-component synthesis of coumarin based luminophores and the tunability of their electronic properties already at the stage of the alkynyl coumarin intermediates [32], we reasoned that the interesting electronic properties of cyclohexanone-based merocyanines as previously shown by Laschat’s group [33] could be valuable targets for an MCR approach based upon our alkynylation-addition strategy. Here, we report the concise consecutive three-component synthesis of cyclohexanone-based merocyanines and the pseudo four-component synthesis of selected cyanines and the investigation of their UV/Vis absorption properties.

2. Results and Discussion

2.1. Synthesis and Structure

Starting from dimedone (1), i.e., 5,5-dimethylcyclohexane-1,3-dione, a suitable (pseudo)halide is generated by reaction with triflic anhydride to give the corresponding triflate 2 in excellent yield according to the literature (Scheme 1) [34,35].
Based upon our experience with alkynylation of coumarin triflates [32] and their use in consecutive three-component alkynylation-addition sequences [30], we first set out to probe the same reaction conditions in a model reaction of triflate 2, (trimethylsilyl)acetylene (3a), and morpholine (4a). To our surprise a mixture of the merocyanine 5a and the cyanine 6a is formed upon heating to 100 °C in the microwave cavity for 1 h, if triethylamine is employed as a base (Scheme 2, Table 1). While merocyanine 5a can be isolated upon flash chromatography, cyanine 6a is only identified in an inseparable fraction by the mass peaks of the cation and the triflate in the HRMS (Table 1, entries 1–3). However, no product is obtained upon altering the base of the alkynylation step to Hünig’s base (DIPEA) (Table 1, entry 4), while employing potassium carbonate (Table 1, entries 5 and 6) exclusively produces the merocyanine 5a.
Starting from triflate 2, alkyne 3, and heterocyclic secondary amine 4, potassium carbonate and triethylamine can both be successfully employed in the alkynylation step of the three-component syntheses of merocyanines 5; however, in most cases the former base gives higher yields after isolation by flash chromatography (Scheme 3).
Moreover, Fischer’s base (7) can be employed in the addition step of the consecutive merocyanine synthesis using triethylamine as the base in the alkynylation step, albeit, with only a poor overall yield of merocyanine 8 (Scheme 4).
Intrigued by the formation of cyanine 6a as a byproduct and employing pyrrolidine (4b) as a stronger nucleophile, we set out to probe the selective formation of cyanines 6 in a pseudo four-component fashion. Indeed, upon reaction of triflate 2, alkynes 3 (R1 = SiMe3 or Ph), and pyrrolidine (4b) in the presence of triethylamine as a base in the alkynylation step, cyanines 6 is obtained analytically pure and in excellent yield as triflate salts after chromatography on silica gel (Scheme 5). It is noteworthy to mention that piperidine (4c) is obviously not nucleophilic enough to give complete conversion to the corresponding cyanine, which is only identified in the inseparable fraction after flash chromatography.
The structures of the merocyanines 5 and 8 and the cyanines 6 were unambiguously assigned by NMR spectroscopy and mass spectrometry. The representative discussion of extensive NMR spectroscopy of compound 5e underlines some features of the merocyanines. The geminal methyl groups on the cyclohexenone moiety appear as a singlet at δ 0.79, indicating the overall planar structure of the merocyanine chromophore in solution (Figure 1). The methylene protons in α- and γ-position to the carbonyl group appear as singlets at δ 2.01 and 1.65. Methine signals for the α- and the γ-positions of the Michael system are expectedly found a higher field and appear as singlets at δ 5.05 and 5.41. The methylene protons of the pyrrolidinyl moiety are not well resolved and are found at δ 1.89 and 3.15.
The E-configuration of the pyrrolidinyl vinyl substituent can be assigned by the NOESY spectrum, where the pyrrolidinyl α-protons at δ 3.15 and the cyclohexenyl methylene protons at δ 1.65 give cross-peaks to the merocyanine methine proton at δ 5.05 (Figure 2).
In addition, the structure of cyanine 6b was corroborated by an X-ray structure analysis (Figure 3) [36], which clearly shows that an E-configured isomer was formed in the synthesis. Furthermore, the inspection of the bond lengths of the fully planarized pentamethine part of the chromophore supports the highly delocalized cyanine structure with a small bond length alternation [37] of 0.027 Å for the bonds C1-C6, C6-C5, C5-C7, and C7-C8 (Table 2, entries 2–5), which is typical for nearly symmetrical electron density distribution in cationic cyanine dyes [38].

2.2. Absorption and Emission Characteristics

Merocyanines 5 and 8 and cyanines 6 that are obtained as yellow to orange solids were investigated by UV/Vis and emission spectroscopy in dichloromethane solution (Table 3). The merocyanines 5 give typically broad, unstructured longest wavelength absorption bands between 365 and 388 nm (Figure 4, Table 3, entries 1–5), also revealing that the maxima redshift with increasing electron donicity of the secondary amine from morpholine over piperidine to pyrrolidine. Extension of the π-system as for merocyanine 8 expectedly causes a redshift of the absorption band to 442 nm (Table 3, entry 6). The absorption solvatochromicity in qualitative UV/Vis measurements is small, similarly as reported for more rigidified merocyanines [33] accounting for a more polyene-like ground state structure of merocyanines 5 and 8. None of the merocyanines, neither 5 nor 8, display any emission upon detection with the naked eye and attempted emission spectroscopy also remains unsuccessful. The cyanines 6b and 6c possess cyanine typical narrow absorption bands at 443 and 459 nm with absorption coefficients exceeding 105 M 1cm 1 (Figure 5, Table 3, entries 7 and 8). Both cyanines are weakly emissive with a sharp emission maximum at 453 nm for cyanine 6b, indicating minimal structural changes in the vibrationally relaxed S1 after photonic excitation, and a broad emission maximum at 513 nm for cyanine 6c. The latter large Stokes shift of 2300 cm 1 accounts for more pronounced structural changes upon electronic excitation from the electronic ground state S0 to the vibrationally relaxed S1.

2.3. Calculated Electronic Structure

For assigning the photophysical characteristics of merocyanines 5 and cyanines 6, calculations of the UV/Vis transitions of geometry optimized structures of merocyanine 5b and cyanine 6b were performed on the DFT and TDDFT level of theory using various exchange correlation hybrid functionals (B3LYP [39], PBEh1PBE [40], and CAM-B3LYP [41]) and the 6-311++G** basis set [42], which was chosen to most precisely describe polarization as well as long-range interactions. Besides gas phase calculations, the polarizable continuum model (PCM) for the dichloromethane as a dielectric continuum is employed [43] as implemented in the program package Gaussian 16 [44]. The comparative calculations of the first excited states S1 to S6 are summarized in Table 4 (merocyanine 5b) and Table 5 (cyanine 6b). The longest wavelength absorption bands possess high extinction coefficients in the experimental spectra and this aspect is mirrored by high oscillatory strengths in the calculated spectra (see Supplementary Materials).
For merocyanine 5b, the longest wavelength band apparently depends on solvent stabilization (Table 4). While gas phase calculations with B3LYP, PBEh1PBE, and CAM-B3LYP functionals predict lowest energy bands of weak intensity dominated by an n-π* (HOMO-1→LUMO) transition as singlet S1 state, the highest intensity π-π* (HOMO→LUMO) transition represents the S2 state. The solvation effect becomes apparent for all functionals upon employing the implicit PCM for dichloromethane as a continuum, which was actually also used in experimental spectroscopy. For PCM calculations, the lowest energy, highest intensity band predominantly consists of π-π* (HOMO→LUMO) transition, yet, with a minor contribution of the n-π* (HOMO-1→LUMO) transition in singlet S1 state as shown for the B3LYP with state specific solvation. As seen for all merocyanines 5, emission cannot be detected by the naked eye nor with steady state fluorescence spectroscopy (vide supra).
All TDDFT calculations on merocyanine 5b give higher energies for the lowest energy band than the experimentally determined values by 0.127 to 0.775 eV. Indeed, the smallest deviations are found for the functionals B3LYP (0.127 eV) and PBEh1PBE (0.191 eV) with explicit PCM implementation. These deviations fall into the same range as previously reported for TDDFT calculations on cyanines [45]. The Kohn-Sham frontier molecular orbitals of the B3LYP/6-311++G** PCM calculations nicely illustrate that the intense longest wavelength absorption is dominated by HOMO→LUMO transition along the chromophore axis (Figure 6, left). The less dominant, weak intensely HOMO-1→LUMO transition clearly possesses n-π* character. In the experiment, this transition might fall in superposition with the broad intense merocyanine π-π* band.
Expectedly for cyanine 6b, the PCM solvent implementation predicts the absorption to arise at longer wavelengths in comparison to the gas phase calculations (Table 5). For all exchange correlation hybrid functionals the lowest energy transition is fully represented by HOMO→LUMO transition along the cyanine chromophore axis, as also seen in the Kohn-Sham frontier molecular orbitals (Figure 6, right). As stated above and typical for cyanines, the calculated transition energies for this band are higher and deviate by 0.402 to 0.686 eV in comparison to the experimentally determined absorption energy. As mentioned before, the functionals B3LYP (0.402 eV) and PBEh1PBE (0.451 eV) with explicit PCM implementation possess the smallest deviations.

3. Conclusions

The triflate readily accessible from dimedone is a favorable starting material for consecutive three-component alkynylation-addition sequences to merocyanines with embedded butadiene structure in moderate to excellent yield. Moreover, employing pyrrolidine as an amino component enables a pseudo four-component synthesis of related cyanines by carbonyl condensation of the heterocyclic amine in excellent yield. While butadiene-based (absorption between 360 and 390 nm) and expanded hexatriene (absorption at 442 nm) chromophores are essentially nonfluorescent in solution and in the solid state, the pentamethine cyanines absorb intensively at 443 and 459 nm and also luminesce in solution with low fluorescence quantum yield of 1%. According to TDDFT calculations with various exchange correlation hybrid functionals in the gas phase and in an explicit continuum of dichloromethane, the electronic structure of the longest wavelength absorption bands is highly solvent dependent for both a representative merocyanine and a cyanine. The cyanine typical deviation of calculated transitions to higher energies in comparison to the experimental data falls in a regime of 0.127 eV for the merocyanine and 0.402 eV for the model cyanine. For merocyanines, the lowest energy absorption band contains n-π* character, which plausibly accounts for the indiscernible luminescence. In contrast, the rigidified cyanine’s lowest energy band is exclusively a π-π* transition and does not interfere with luminescence. The synthetic ease of accessing both merocyanines and cyanines in a one-pot fashion allows for readily preparing substance libraries of both chromophore types, which can be interesting for biophysical analytics. Studies directed to expand the one-pot methodology to bathochromically shifted merocyanines based upon the dimedone derived triflate are currently underway.

4. Experimental

4.1. 5,5-Dimethyl-3-oxocyclohex-1-en-1-yl trifluoromethanesulfonate (2)

In a Schlenk flask with magnetic stir bar, dimedone (1) (2.80 g, 20.0 mmol) was dissolved in dichloromethane (50 mL) under nitrogen and the solution was cooled to 0 °C (ice water bath) before pyridine (2.00 mL, 24.8 mmol) was added. Trifluoromethanesulfonic anhydride (3.90 mL, 23.2 mmol) was added dropwise to the cooled solution over a period of 1 h. The cooling was stopped and the reaction mixture was stirred at room temp for 2 h. Then, a 1 M aqueous HCl solution (25 mL) was added. The organic layer was washed with a saturated aqueous NaHCO3 solution (3 × 20 mL) and dried (anhydrous Na2SO4). After filtration and removal of the solvents in vacuo, the crude product was purified by flash chromatography on silica gel (n-hexane/ethyl acetate 98:2) to give compound 1 [34] (4.94 g, 91%) as a pale-yellow liquid, Rf (n-hexane/ethyl acetate 20:1): 0.14.
1H NMR (600 MHz, CDCl3): δ 1.13 (s, 6 H), 2.30 (s, 2 H), 2.54 (d, J = 1.3 Hz, 2 H), 6.06 (t, J = 1.3 Hz, 1 H). 13C NMR (151 MHz, CDCl3): δ 28.1 (CH3), 33.5 (Cquat), 42.4 (CH2), 50.6 (CH2), 118.4 (CH), 118.5 (Cquat, q, 1JC-F = 321 Hz), 166.1 (Cquat), 197.6 (Cquat). EI MS (70 eV, m/z (%)): 272 (18, [M+]), 244 (15, [C8H11O3SF3+]), 216 (100), 86 (28), 83 (16), 69 (38, [CF3+]), 56 (10), 55 (11), 41 (12).

4.2. General Procedure (GP) for the Three-Component Synthesis of Merocyanines 5 and 8

PdCl2(PPh3)2 (14 mg, 0.02 mmol), CuI (7 mg, 0.04 mmol), compound 2 (272 mg, 1.00 mmol), and dry, degassed THF (1 mL) were placed in a microwave vessel. The solution was saturated with a constant stream of nitrogen through a syringe for 5 min. Then, alkyne 3 (1.0 mmol), K2CO3 (166 mg, 1.20 mmol), or triethylamine (0.14 mL, 1.00 mmol) were added and the mixture was stirred at room temp for 1 h (for experimental details, see Table 6). Then, the amine 4 or Fischer’s base (7) (1.0 mmol) and methanol (1 mL) were added to the reaction mixture. The reaction mixture was then heated in the microwave cavity at 100 °C for 1 h. After cooling to room temp, the solvents were removed under reduced pressure and the residue was purified by flash chromatography on silica gel (n-hexane/ethyl acetate) to give the analytically pure product merocyanine 5 and 8.

4.3. (E)-5,5-Dimethyl-3-(2-morpholinovinyl)cyclohex-2-en-1-one (5a)

According to the GP and after chromatography on silica gel (n-hexane/ethyl acetate 2:1) and drying under vacuum, compound 5a (135 mg, 65%, with potassium carbonate as a base; 82 mg, 35%, with triethylamine as a base) was obtained as an orange solid, mp 72 °C, Rf (n-hexane/ethyl acetate 2:1): 0.12.
1H NMR (600 MHz, MeOD-d4): δ 1.08 (s, 6 H), 2.22 (s, 2 H), 2.43 (s, 2 H), 3.34 (t, J = 4.7 Hz, 4 H), 3.73 (t, J = 4.9 Hz, 4 H), 5.43 (d, J = 13.5 Hz, 1 H), 5.71 (s, 1 H), 7.15 (d, J = 13.5 Hz, 1 H). 13C NMR (151 MHz, MeOD-d4): δ 28.5 (CH3), 34.0 (Cquat), 40.2 (CH2), 49.7 (CH2), 51.4 (CH2), 67.2 (CH2), 100.4 (CH), 116.3 (CH), 148.0 (CH), 164.4 (Cquat), 200.9 (Cquat). EI MS (70 eV, m/z (%)): 236 (18), 235 (100, [M+]), 222 (10), 221 (11), 220 (31, [C13H18NO2+]), 214 (15), 207 (19, [C12H17NO2+]), 206 (16), 192 (22), 179 (13, [C10H13NO2+]), 178 (31), 153 (12), 152 (13), 151 (15, [C9H13NO+]), 150 (18), 149 (20, [C10H13O+]), 138 (19, [C8H12NO+]), 136 (48, [C9H12O+]), 135 (11), 122 (20), 121 (41), 120 (13), 112 (12, [C6H10NO+]), 107 (16), 106 (11), 105 (15), 100 (11), 94 (17), 93 (56), 91 (11), 86 (17, [C4H8NO+]), 85 (20), 79 (14), 77 (14), 67 (14), 65 (12), 57 (10), 56 (14), 55 (21), 42 (10), 41 (13). IR: ν ~ [cm−1]: 3053 (w), 3026 (w), 2955 (w), 2926 (w), 2891 (w), 2864 (w), 1589 (s), 1553 (s), 1504 (w), 1443 (m), 1422 (m), 1412 (m), 1375 (m), 1319 (m), 1298 (m), 1277 (s), 1252 (m), 1227 (m), 1194 (m), 1152 (m), 1109 (s), 1069 (m), 1047 (w), 1020 (m), 995 (m), 943 (m), 924 (w), 854 (m), 822 (w), 799 (w), 756 (w), 745 (w), 725 (w), 681 (m), 602 (m). Anal calcd for C14H21NO2 (235.3): C 71.46, H 8.99, N 5.95; Found: C 71.27, H 9.28, N 5.93.

4.4. (E)-5,5-Dimethyl-3-[2-(pyrrolidin-1-yl)vinyl]cyclohex-2-en-1-one (5b)

According to the GP and after chromatography on silica gel (n-hexane/ethyl acetate 3:1) and drying under vacuum, compound 5b (116 mg, 53%) was obtained as a yellow solid, mp 125 °C, Rf (n-hexane/ethyl acetate/NEt3 200:100:3): 0.14.
1H NMR (600 MHz, CDCl3): δ 1.04 (s, 6 H), 1.94 (t, J = 6.6 Hz, 4 H), 2.20 (s, 2 H), 2.27 (s, 2 H), 3.30 (t, J = 6.7 Hz, 4 H), 5.04 (d, J = 13.4 Hz, 1 H), 5.70 (s, 1 H), 7.08 (d, J = 13.3 Hz, 1 H). 13C NMR (151 MHz, CDCl3): δ 25.1 (CH2), 28.5 (CH3), 33.0 (Cquat), 39.6 (CH2), 49.1 (CH2), 50.9 (CH2), 99.2 (CH), 116.2 (CH), 141.4 (CH), 158.9 (Cquat), 198.3 (Cquat). EI MS (70 eV, m/z (%)): 220 (19), 219 (100, [M+]), 204 (55, [C13H18NO+]), 191 (11, [C12H17NO+]), 190 (16), 176 (23), 163 (10, [C10H13NO+]), 162 (20), 136 (17, [C9H12O+]), 135 (42, [C9H13N+]), 134 (86), 122 (13, [C8H12N+]), 121 (10), 120 (43), 107 (59), 106 (16), 93 (12), 79 (11), 70 (10, [C4H8N+]). IR: ν ~ [cm−1]: 3051 (w), 3013 (w), 2990 (w), 2955 (w), 2926 (w), 2857 (w), 1636 (w), 1585 (s), 1560 (s), 1550 (s), 1545 (s), 1533 (m), 1481 (m), 1459 (w), 1452 (w), 1406 (m), 1383 (s), 1369 (s), 1358 (s), 1315 (m), 1306 (m), 1292 (m), 1275 (s), 1248 (s), 1194 (m), 1161 (m), 1148 (s), 1119 (s), 1032 (w), 1018 (w), 980 (m), 924 (w), 912 (w), 891 (m), 866 (m), 847 (s), 806 (w), 791 (m), 704 (w), 606 (m). UV/Vis (CH2Cl2): λmax [nm] (ε [Lcm−1mol−1]): 373 (71000). Anal calcd for C14H21NO (219.3): C 76.67, H 9.65, N 6.39; Found: C 76.43, H 9.94, N 6.17.

4.5. (E)-5,5-Dimethyl-3-(2-morpholino-2-phenylvinyl)cyclohex-2-en-1-one (5c)

According to the GP and after chromatography on silica gel (n-hexane/ethyl acetate 3:1) and drying under vacuum, compound 5c (171 mg, 55%, with potassium carbonate as a base; 212 mg, 68%, with triethylamine as a base) was obtained as a yellow solid, mp 78 °C, Rf (n-hexane/ethyl acetate 3:1): 0.09.
1H NMR (600 MHz, DMSO-d6): δ 0.76 (s, 6 H), 1.75 (s, 2 H), 1.92 (s, 2 H), 2.94 (t, J = 4.8 Hz, 4 H), 3.60 (t, J = 4.8 Hz, 4 H), 5.30 (s, 1 H), 5.28 (s, 1 H), 7.16–7.32 (m, 2 H), 7.37–7.48 (m, 3 H). 13C NMR (151 MHz, DMSO-d6): δ 27.8 (CH3), 32.9 (Cquat), 43.4 (CH2), 48.3 (CH2), 50.3 (CH2), 65.8 (CH2), 103.9 (CH), 121.1 (CH), 128.8 (CH), 129.3 (CH), 129.4 (CH), 136.4 (Cquat), 156.2 (Cquat), 157.9 (Cquat), 196.9 (Cquat). EI MS (70 eV, m/z (%)): 312 (22), 311 (100, [M+]), 310 (26), 296 (11, [C19H22NO2+]), 295 (17), 294 (76), 254 (19), 252 (11), 227 (14, [C15H17NO+]), 226 (13), 225 (21, [C16H17O+]), 212 (32), 198 (11), 196 (12), 170 (11), 169 (14), 168 (15), 141 (15), 105 (60), 77 (17, [C6H5+]), 43 (11). IR: ν ~ [cm−1]: 3030 (w), 2963 (w), 2932 (w), 2913 (w), 2899 (w), 2855 (w), 2822 (w), 1639 (m), 1579 (m), 1570 (s), 1557 (m), 1539 (m), 1489 (w), 1443 (m), 1437 (w), 1387 (m), 1358 (m), 1314 (w), 1298 (m), 1281 (m), 1267 (m), 1248 (w), 1225 (s), 1214 (m), 1204 (s), 1175 (w), 1148 (w), 1111 (s), 1077 (w), 1069 (m), 1030 (m), 1020 (m), 999 (w), 941 (w), 932 (m), 903 (w), 889 (m), 883 (m), 862 (m), 849 (m), 808 (w), 777 (s), 735 (m), 710 (m), 692 (m), 644 (w), 623 (m). UV/Vis (CH2Cl2): λmax [nm] (ε [Lcm−1mol−1]): 365 (19000). Anal calcd for C20H25NO2 (311.4): C 77.14, H 8.09, N 4.50; Found: C 76.90, H 8.33, N 4.34.

4.6. (E)-5,5-Dimethyl-3-[2-phenyl-2-(piperidin-1-yl)vinyl]cyclohex-2-en-1-one (5d)

According to the GP and after chromatography on silica gel (n-hexane/ethyl acetate/NEt3 500:100:6) and drying under vacuum, compound 5d (191 mg, 62%, with potassium carbonate as a base; 62 mg, 20%, with triethylamine as a base) was obtained as an orange solid, mp 86 °C, Rf (n-hexane/ethyl acetate/NEt3 500:100:6): 0.08.
1H NMR (600 MHz, CDCl3): δ 0.80 (s, 6 H), 1.53–1.56 (m, 2 H), 1.56–1.63 (m, 4 H), 1.68 (s, 2 H), 2.03 (s, 2 H), 3.02 (t, J = 5.2 Hz, 4 H), 5.23 (s, 1 H), 5.48 (s, 1 H), 7.23–7.25 (m, 2 H), 7.33–7.42 (m, 3 H). 13C NMR (151 MHz, CDCl3): δ 24.5 (CH2), 25.9 (CH2), 28.2 (CH3), 33.5 (Cquat), 44.1 (CH2), 49.7 (CH2), 50.9 (CH2), 104.1 (CH), 121.3 (CH), 128.7 (CH), 129.3 (CH), 129.7 (CH), 137.6 (Cquat), 157.7 (Cquat), 159.9 (Cquat), 199.0 (Cquat). EI MS (70 eV, m/z (%)): 310 (15), 309 (68, [M+]), 308 (28), 294 (10, [C20H24NO+]), 293 (16), 292 (68), 280 (11, [C19H21NO+]), 253 (10, [C17H19NO+]), 252 (41), 225 (19, [C16H17O+]), 224 (29), 211 (20), 210 (100, [C15H14O+]), 196 (10), 170 (13), 141 (15), 115 (11), 105 (12), 104 (10), 84 (14, [C5H10N+]). IR: ν ~ [cm−1]: 2988 (w), 2936 (w), 2864 (w), 2828 (w), 1628 (m), 1576 (w), 1561 (m), 1551 (s), 1546 (s), 1541 (s), 1534 (s), 1522 (m), 1518 (m), 1508 (m), 1491 (w), 1462 (w), 1449 (m), 1441 (m), 1420 (w), 1370 (m), 1364 (m), 1302 (m), 1279 (m), 1263 (w), 1227 (s), 1202 (m), 1157 (w), 1138 (m), 1119 (m), 1101 (s), 1070 (w), 1028 (w), 1007 (w), 918 (w), 895 (m), 880 (m), 860 (m), 851 (m), 831 (m), 818 (w), 797 (w), 777 (s), 725 (m), 702 (m), 675 (m), 638 (w), 606 (m). UV/Vis (CH2Cl2): λmax [nm] (ε [Lcm−1mol−1]): 383 (22000). HRMS (ESI, m/z (%)) calcd for [C21H28NO]+: 310.2165 (100), 311.2199 (23), 312.2233 (3); Found: 310.2170 (100), 311.2201 (19), 312.2231 (3).

4.7. (E)-5,5-Dimethyl-3-[2-phenyl-2-(pyrrolidin-1-yl)vinyl]cyclohex-2-en-1-one (5e)

According to the GP and after chromatography on silica gel (n-hexane/ethyl acetate/NEt3 200:100:3) and drying under vacuum, compound 5e (118 mg, 40%) was obtained as an orange solid, mp 133 °C, Rf (n-hexane/ethyl acetate/NEt3 200:100:3): 0.17.
1H NMR (600 MHz, CDCl3): δ 0.78 (s, 6 H), 1.65 (s, 2 H), 1.89 (t, J = 6.7 Hz, 4 H), 2.01 (s, 2 H), 3.15 (t, J = 6.3 Hz, 4 H), 5.05 (s, 1 H), 5.41 (s, 1 H), 7.19–7.25 (m, 2 H), 7.35–7.47 (m, 3 H). 13C NMR (151 MHz, CDCl3): δ 25.4 (CH2), 28.3 (CH3), 33.2 (Cquat), 44.0 (CH2), 49.2 (CH2), 50.7 (CH2), 100.2 (CH), 118.4 (CH), 128.6 (CH), 128.9 (CH), 129.0 (CH), 137.9 (Cquat), 154.9 (Cquat), 159.8 (Cquat), 198.6 (Cquat). EI MS (70 eV, m/z (%)): 296 (15), 295 (73, [M+]), 294 (24), 280 (34, [C19H22NO+]), 279 (21), 278 (94), 239 (11, [C16H17NO+]), 238 (32), 211 (18, [C15H17N+]), 210 (31), 197 (21, [C14H15N+]), 196 (100), 183 (10), 182 (15), 170 (12), 168 (11), 167 (10), 142 (10), 141 (17), 115 (13), 105 (11). IR: ν ~ [cm−1]: 3057 (w), 2945 (w), 2978 (w), 2864 (w), 2843 (w), 1620 (m), 1533 (s), 1501 (m), 1474 (m), 1453 (m), 1445 (m), 1425 (m), 1366 (s), 1344 (m), 1315 (m), 1302 (s), 1279 (s), 1254 (m), 1229 (m), 1204 (s), 1179 (m), 1165 (m), 1140 (s), 1109 (s), 1074 (m), 1028 (w), 991 (m), 970 (w), 937 (w), 924 (m), 893 (m), 885 (m), 876 (s), 864 (m), 804 (w), 775 (s), 743 (w), 706 (s), 691 (m), 673 (w), 631 (w). UV/Vis (CH2Cl2): λmax [nm] (ε [Lcm−1mol−1]): 388 (43000). Anal calcd for C20H25NO (295.4): C 81.31, H 8.53, N 4.74; Found: C 81.02, H 8.80, N 4.58.

4.8. 5,5-Dimethyl-3-[(E)-3-((E)-1,3,3-trimethylindolin-2-yliden)prop-1-en-1-yl]cyclohex-2-en-1-one (8)

According to the GP and after chromatography on silica gel (n-hexane/ethyl acetate/NEt3 300:100:4) and drying under vacuum, compound 8 (21 mg, 7%) was obtained as an orange solid, mp 86 °C, Rf (n-hexane/ethyl acetate/NEt3 300:100:4): 0.31.
1H NMR (600 MHz, CDCl3): δ 1.10 (s, 6 H), 1.61 (s, 6 H), 2.27 (s, 2 H), 2.39 (s, 2 H), 3.15 (s, 3 H), 5.42 (d, J = 12.0 Hz, 1 H), 5.90 (s, 1 H), 6.11 (d, J = 14.6 Hz, 1 H), 6.66 (d, 3J = 7.8 ν ~ Hz, 1 H), 6.89 (t, J = 7.4 Hz, 1 H), 7.13–7.21 (m, 2 H), 7.30 (dd, J = 14.8, 12.0 Hz, 1 H). 13C NMR (151 MHz, CDCl3): δ 28.7 (CH3), 28.8 (CH3), 29.3 (CH3), 33.4 (Cquat), 39.7 (CH2), 46.1 (Cquat), 51.5 (CH2), 96.5 (CH), 106.6 (CH), 120.4 (CH), 121.7 (CH), 122.3 (CH), 124.6 (CH), 128.0 (CH), 132.9 (CH), 138.9 (Cquat), 144.8 (Cquat), 156.9 (Cquat), 160.8 (Cquat), 199.9 (Cquat). IR: ν ~ [cm−1]: 3049 (w), 2955 (w), 2924 (w), 2864 (w), 1641 (w), 1618 (m), 1595 (m), 1576 (m), 1541 (s), 1537 (s), 1489 (m), 1456 (m), 1375 (m), 1364 (m), 1350 (m), 1339 (m), 1314 (m), 1300 (m), 1273 (s), 1246 (m), 1204 (m), 1182 (m), 1165 (m), 1148 (s), 1115 (s), 1078 (m), 1042 (w), 1030 (w), 1020 (m), 993 (w), 959 (m), 930 (m), 897 (w), 878 (m), 858 (m), 831 (w), 806 (m), 797 (m), 741 (s), 716 (w), 656 (w), 637 (w), 604 (w). UV/Vis (CH2Cl2): λmax [nm] (ε [Lcm−1mol−1]): 275 (14000), 442 (27000). HRMS (ESI) calcd for [C22H28NO]+: 322.2165 (100), 323.2199 (24), 324.2233 (3); Found: 322.2169 (100), 323.2203 (23), 324.2233 (3).

4.9. General Procedure (GP) for the Pseudo Four-Component Synthesis of Cyanines 6

PdCl2(PPh3)2 (14 mg, 0.02 mmol), CuI (7 mg, 0.04 mmol), compound 13 (272 mg, 1.00 mmol), and dry, degassed THF (1 mL) were placed in a microwave vessel. The solution was saturated with a constant stream of nitrogen through a syringe for 5 min. Then, alkyne 7 (1.0 mmol) and triethylamine (0.14 mL, 1.00 mmol) were added and the mixture was stirred at room temp for 1 h (for experimental details, see Table 7). Then, the pyrrolidine (9c) (1.0 mmol) and methanol (1 mL) were added to the reaction mixture. The reaction mixture was then heated in the microwave cavity at 100 °C for 1 h. After cooling to room temp the solvents were removed under reduced pressure and the residue was purified by flash chromatography on silica gel (n-hexane/ethyl acetate) to give the analytically pure product 6.

4.10. (E)-1-{5,5-Dimethyl-3-[2-(pyrrolidin-1-yl)vinyl]cyclohex-2-en-1-ylidene}pyrrolidin-1-ium (6b)

According to the GP, upon reaction of alkyne 7a (140 μL, 0.98 mmol) and pyrrolidine (9c) (85 μL, 1.00 mmol) and after chromatography on silica gel (n-hexane/ethyl acetate/Net3 200:100:3) and drying under vacuum, compound 6b (209 mg, 99%) was obtained as an orange solid, mp 180 °C, Rf (ethyl acetate): 0.05.
1H NMR (600 MHz, 298 K, acetone-d6): δ 1.07 (s, 6 H), 1.97 (quint, J = 6.9 Hz, 3 H), 2.03 (s, 1 H), 2.09 (q, J = 7.1 Hz, 4 H), 2.55 (s, 2 H), 2.60 (s, 2 H), 3.46 (t, J = 7.2 Hz, 2 H), 3.64 (t, J = 6.8 Hz, 2 H), 3.69–3.85 (m, 4 H), 5.68 (d, J = 12.7 Hz, 1 H), 5.93 (s, 1 H), 8.08 (d, J = 12.6 Hz, 1 H). 1H NMR (600 MHz, 261 K, acetone-d6): δ 1.04 (s, 6 H), 1.95 (t, J = 6.8 Hz, 2 H), 2.00–2.04 (m, 4 H), 2.06–2.10 (m, 2 H), 2.53 (s, 2 H), 2.59 (s, 2 H), 3.44 (t, J = 7.1 Hz, 2 H), 3.62 (t, J = 6.8 Hz, 2 H), 3.73 (t, J = 6.8 Hz, 2 H), 3.76 (t, J = 6.7 Hz, 2 H), 5.67 (d, J = 12.6 Hz, 1 H), 5.92 (s, 1 H), 8.09 (d, J = 12.6 Hz, 1 H). 13C NMR (151 MHz, 298 K, acetone-d6): δ 25.2 (CH2), 25.5 (CH2), 25.6 (CH2), 28.2 (CH3), 32.6 (Cquat), 38.9 (CH2), 42.7 (CH2), 48.3 (CH2), 50.5 (CH2), 54.1 (CH2), 104.1 (CH), 104.9 (CH), 122.2 (Cquat, q, 1JC-F = 322 Hz), 151.3 (CH), 165.8 (Cquat), 168.2 (Cquat). 13C NMR (151 MHz, 261 K, acetone-d6): δ 25.1 (CH2), 25.4 (CH2), 25.4 (CH2), 25.5 (CH2), 28.1 (CH3), 32.4 (Cquat), 38.6 (CH2), 42.3 (CH2), 48.1 (CH2), 50.3 (CH2), 50.4 (CH2), 53.8 (CH2), 103.8 (CH), 104.5 (CH), 121.9 (Cquat, q, 1JC-F = 321 Hz), 151.1 (CH), 165.4 (Cquat), 167.8 (Cquat). HR MS (ESI, m/z (%)) calcd for [C18H29N2]+: 273.2325 (100), 274.2359 (20), 275.2392 (2); Found: 273.2327 (100), 274.2359 (18), 275.2389 (2). IR: ν ~ [cm−1]: 2984 (w), 2957 (w), 2872 (w), 1624 (w), 1522 (m), 1477 (w), 1441 (m), 1412 (m), 1396 (w), 1375 (m), 1348 (m), 1337 (w), 1325 (w), 1262 (s), 1248 (s), 1233 (m), 1221 (s), 1152 (s), 1103 (m), 1026 (s), 1005 (w), 986 (w), 966 (w), 947 (w), 924 (w), 912 (w), 883 (m), 876 (m), 853 (m), 781 (w), 766 (w), 754 (w), 706 (w), 633 (s). UV/Vis (CH2Cl2): λmax [nm] (ε [L·cm−1·mol−1]): 443 (114000). Emission (CH2Cl2): λmax [nm]: 459. Stokes shift [cm−1]: 800. Anal calcd for C19H29F3N2O3S (422.5): C 54.01, H 6.92, N 6.63, S 7.59; Found: C 54.04, H 7.21, N 6.54, S 7.48.

4.11. €-1-{5,5-Dimethyl-3-[2-phenyl-2-(pyrrolidin-1-yl)vinyl]cyclohex-2-en-1-yliden}pyrrolidin-1-ium (6c)

According to the GP, upon reaction of alkyne 7d (110 μL, 1.00 mmol) and pyrrolidine (9c) (85 μL, 1.00 mmol) and after chromatography on silica gel (n-hexane/ethyl acetate/NEt3 200:100:3) and drying under vacuum, compound 6c (214 mg, 86%) was obtained as an orange solid, mp 147 °C, Rf (ethyl acetate/MeOH 3:1): 0.07.
1H NMR (600 MHz, 298 K, DMSO-d6): δ 0.83 (s, 6 H), 1.82–1.85 (m, 6 H), 1.94 (s, 2 H), 2.00–2.04 (m, 2 H), 2.33 (s, 2 H), 2.91 (s, 2 H), 3.19 (t, J = 7.9 Hz, 2 H), 3.48–3.53 (m, 2 H), 3.60 (t, J = 7.7 Hz, 2 H), 5.11 (s, 1 H), 5.52 (s, 1 H), 7.34–7.38 (m, 2 H), 7.45–7.78 (m, 3 H). 1H NMR (600 MHz, 298 K, acetone-d6): δ 0.90 (s, 6 H), 1.89–1.96 (m, 6 H), 2.06–2.07 (m, 1 H), 2.08–2.09 (m, 1 H), 2.10–2.14 (m, 2 H), 2.41 (s, 2 H), 2.99 (s, 2 H), 3.28–3.36 (m, 2 H), 3.61–3.65 (m, 2 H), 3.65–3.73 (m, 2 H), 5.19 (s, 1 H), 5.57 (s, 1 H), 7.40–7.44 (m, 2 H), 7.58–7.66 (m, 3 H). 1H NMR (600 MHz, 261 K, acetone-d6): δ 0.89 (s, 6 H), 1.91 (q, J = 6.9 Hz, 6 H), 2.08–2.14 (m, 3 H), 2.40 (s, 2 H), 3.14 (s, 3 H), 3.24–3.38 (m, 2 H), 3.62 (s, 2 H), 3.67 (t, J = 7.0 Hz, 2 H), 4.66 (s, 1 H), 5.15–6.24 (m, 1 H), 7.37–7.49 (m, 2 H), 7.56–7.70 (m, 3 H). 13C NMR (151 MHz, 298 K, DMSO-d6): δ 24.0 (CH2), 24.3 (CH2), 24.6 (CH2), 24.7 (CH2), 27.5 (CH3), 31.5 (Cquat), 40.9 (CH2), 48.9 (Cquat), 49.3 (CH2), 49.7 (CH2), 51.4 (CH2), 120.7 (Cquat, d, JC-F = 322 Hz), 127.2 (CH), 127.2 (CH), 129.7 (CH), 129.9 (CH), 129.9 (CH), 136.4 (Cquat), 162.5 (Cquat), 163.5 (Cquat). 13C NMR (151 MHz, 298 K, acetone-d6): δ 25.0 (CH2), 25.4 (CH2), 25.6 (CH2), 25.7 (CH2), 28.0 (CH3), 30.4 (CH2), 30.6 (CH), 32.5 (Cquat), 42.3 (CH2), 50.0 (CH2), 50.4 (CH2), 50.7 (CH2), 52.4 (CH2), 122.4 (Cquat, q, JC-F = 322 Hz), 128.2 (CH), 130.7 (CH), 130.8 (CH), 137.8 (Cquat), 164.2 (Cquat), 165.0 (Cquat), 167.0 (Cquat). 13C NMR (151 MHz, 261 K, acetone-d6): δ 24.9 (CH2), 25.2 (CH2), 25.3 (CH2), 25.5 (CH2), 25.6 (CH2), 27.8 (CH3), 30.3 (CH2), 30.6 (CH), 32.4 (Cquat), 41.9 (CH2), 49.8 (Cquat), 50.2 (CH2), 50.5 (CH2), 52.3 (CH2), 52.3 (Cquat), 55.0 (CH), 101.9 (CH), 122.1 (Cquat, q, JC-F = 322 Hz), 127.9 (CH), 130.7 (CH), 137.6 (Cquat), 164.6 (Cquat). ESI MS calcd for [C24H33N2]+: 349.5; Found: 349.7; calcd for [CF3O3S]−: 149.1; Found: 149.1. HR MS (ESI, m/z (%)) calcd for [C24H33N2]+: 349.2638 (100), 350.2672 (26); Found: 349.2640 (100), 350.2671 (18). IR: ν ~ [cm−1] = 2955 (w), 2922 (w), 2872 (w), 1526 (w), 1504 (m), 1495 (m), 1472 (m), 1439 (m), 1410 (m), 1383 (m), 1346 (w), 1319 (m), 1292 (w), 1261 (s), 1238 (m), 1219 (s), 1180 (m), 1138 (s), 1105 (m), 1028 (s), 999 (w), 953 (w), 922 (w), 914 (w), 881 (m), 864 (m), 845 (m), 820 (m), 793 (w), 772 (m), 752 (w), 706 (w), 692 (m), 635 (s), 611 (m). UV/Vis (CH2Cl2): λmax [nm] (ε [L·cm−1·mol−1]): 459 (130000). Emission (CH2Cl2): λmax [nm]: 513. Stokes shift [cm−1]: 2300. Anal calcd for C25H33F3N2O3S (498.6): C 60.22, H 6.67, N 5.62, S 6.43; Found: C 60.27, H 6.75, N 5.56, S 6.16.

Supplementary Materials

The following are available online at https://www.mdpi.com/article/10.3390/photochem2030044/s1. Figure S1: Three kinds of helix chains constitute the channel column of NUM-14. Figure S2: Comparison of simulated, experimental, and activated PXRD patterns of NUM-14. Figure S3. TGA curve for NUM-14 under Ar atmosphere. Figure S4: The PXRD patterns for NUM-14 after immersed in common solvents a week. Figure S5. The details of Virial equation (solid lines) fitting to the experimental C2H2 adsorption data (symbols) for NUM-14a. Figure S6: The details of Virial equation (solid lines) fitting to the experimental CO2 adsorption data (symbols) for NUM-14a. Figure S7: The details of Virial equation (solid lines) fitting to the experimental C2H4 adsorption data (symbols) for NUM-14a. Figure S8: The details of dual-site Langmuir-Freundlich isotherm (solid lines) fitting to the experimental C2H2 adsorption data (symbols) for NUM-14a at 273 K. Figure S9: The details of dual-site Langmuir-Freundlich isotherm (solid lines) fitting to the experimental C2H2 adsorption data (symbols) for NUM-14a at 298 K. Figure S10: The details of single-site Langmuir-Freundlich isotherm (solid lines) fitting to the experimental CO2 adsorption data (symbols) for NUM-14a at 273 K. Figure S11. The details of single-site Langmuir-Freundlich isotherm (solid lines) fitting to the experimental CO2 adsorption data (symbols) for NUM-14a at 298 K. Figure S12: The details of dual-site Langmuir-Freundlich isotherm (solid lines) fitting to the experimental C2H4 adsorption data (symbols) for NUM-14a at 273 K. Figure S13: The details of dual-site Langmuir-Freundlich isotherm (solid lines) fitting to the experimental C2H4 adsorption data (symbols) for NUM-14a at 298 K. Table S1: Crystal data and structure refinement parameters for NUM-14 [46,47,48,49].

Author Contributions

The work consists of parts of the Ph.D. thesis of J.P., which is supervised by T.J.J.M. and the B.Sc. thesis of T.G., which was supervised by J.P. The conceptualization was outlined and accompanied by T.J.J.M. Synthetic studies were performed by J.P. and T.G. All analytical assignments and photophysical investigations were performed by J.P. The crystal structure analysis was performed and solved by G.J.R. The DFT and TDDFT computations and interpretations were performed by B.M. Writing—original draft preparation, J.P.; writing—review and editing, T.J.J.M.; project administration and funding acquisition was done by T.J.J.M. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by Deutsche Forschungsgemeinschaft (Mu 1088/9-1) and the Fonds der Chemischen Industrie.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data (spectra and computational input files) are collected in the Supplementary Materials of this article.

Acknowledgments

We cordially thank the Deutsche Forschungsgemeinschaft (Mu 1088/9-1) and the Fonds der Chemischen Industrie for financial support. Computational support and infrastructure were provided by the “Centre for Information and Media Technology” (ZIM) at the University of Düsseldorf (Germany). We thank CeMSA@HHU (Center for Molecular and Structural Analytics @ Heinrich Heine University) for recording the mass-spectrometric and the NMR-spectroscopic data.

Conflicts of Interest

The authors declare no conflict of interest.

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Photochem 02 00044 sch001 550
Scheme 1. Synthesis of triflate 2.
Scheme 1. Synthesis of triflate 2.
Photochem 02 00044 sch001
Photochem 02 00044 sch002 550
Scheme 2. Multi-component formation of merocyanine 5a and cyanine 6a.
Scheme 2. Multi-component formation of merocyanine 5a and cyanine 6a.
Photochem 02 00044 sch002
Photochem 02 00044 sch003 550
Scheme 3. Three-component synthesis of merocyanines 5 employing potassium carbonate or triethylamine as a base in the alkynylation step.
Scheme 3. Three-component synthesis of merocyanines 5 employing potassium carbonate or triethylamine as a base in the alkynylation step.
Photochem 02 00044 sch003
Photochem 02 00044 sch004 550
Scheme 4. Three-component synthesis of merocyanine 8.
Scheme 4. Three-component synthesis of merocyanine 8.
Photochem 02 00044 sch004
Photochem 02 00044 sch005 550
Scheme 5. Pseudo four-component synthesis of cyanines 6.
Scheme 5. Pseudo four-component synthesis of cyanines 6.
Photochem 02 00044 sch005
Photochem 02 00044 g001 550
Figure 1. 1H NMR spectrum of compound 5e (CDCl3, 300 MHz, 298 K).
Figure 1. 1H NMR spectrum of compound 5e (CDCl3, 300 MHz, 298 K).
Photochem 02 00044 g001
Photochem 02 00044 g002 550
Figure 2. NOESY spectrum of compound 5e (CDCl3, 600 MHz, 298 K).
Figure 2. NOESY spectrum of compound 5e (CDCl3, 600 MHz, 298 K).
Photochem 02 00044 g002
Photochem 02 00044 g003 550
Figure 3. Molecular structure of 6b. Displacement ellipsoids are drawn at the 50% probability level; H atoms are drawn with an arbitrary radius.
Figure 3. Molecular structure of 6b. Displacement ellipsoids are drawn at the 50% probability level; H atoms are drawn with an arbitrary radius.
Photochem 02 00044 g003
Photochem 02 00044 g004 550
Figure 4. Normalized absorption spectra of merocyanines 5c–e (recorded in dichloromethane, c(5) = 10−5 M, T = 298 K).
Figure 4. Normalized absorption spectra of merocyanines 5c–e (recorded in dichloromethane, c(5) = 10−5 M, T = 298 K).
Photochem 02 00044 g004
Photochem 02 00044 g005 550
Figure 5. Normalized absorption and emission spectra of cyanines 6b and 6c (recorded in dichloromethane, c(6) = 10−5 M, T = 298 K).
Figure 5. Normalized absorption and emission spectra of cyanines 6b and 6c (recorded in dichloromethane, c(6) = 10−5 M, T = 298 K).
Photochem 02 00044 g005
Photochem 02 00044 g006 550
Figure 6. Selected Kohn-Sham frontier molecular orbitals of merocyanine 5b (left) and cyanine 6b (right) (Gaussian 16 B3LYP/6-311++G**, PCM CH2Cl2, isosurface value at 0.04) and the calculated HOMO, HOMO-1, and LUMO energies, including the energy differences between the frontier molecular orbitals as well as the calculated and experimentally determined absorption wavelength of merocyanine 5b and cyanine 6b.
Figure 6. Selected Kohn-Sham frontier molecular orbitals of merocyanine 5b (left) and cyanine 6b (right) (Gaussian 16 B3LYP/6-311++G**, PCM CH2Cl2, isosurface value at 0.04) and the calculated HOMO, HOMO-1, and LUMO energies, including the energy differences between the frontier molecular orbitals as well as the calculated and experimentally determined absorption wavelength of merocyanine 5b and cyanine 6b.
Photochem 02 00044 g006
Table
Table 1. Effect of the base on the multi-component formation of merocyanine 5a and cyanine 6a.
Table 1. Effect of the base on the multi-component formation of merocyanine 5a and cyanine 6a.
EntryBaseMorpholine (4a) [Equivs]Temperature [°C]Reaction Time [h]Merocyanine 5a aCyanine 6a b
1NEt31100 (MW)135%+
2NEt32100 (MW)121%+
3NEt31rt18n.d.+
4DIPEA1100 (MW)1n.d.n.d.
5K2CO3 c1100 (MW)165%n.d.
6K2CO3 c1RT2167%n.d.
a Yield after chromatography on silica gel, n.d.: not detected on TLC. b The product is impure after chromatography on silica gel, but identified by HRMS in the fraction, n.d.: not detected on TLC. c K2CO3 (2 equivs) is employed as a base and the reaction time of the alkynylation step is 2 h.
Table
Table 2. Selected bond lengths of structure 6b.
Table 2. Selected bond lengths of structure 6b.
EntryBondBond Length [Å]
1N1-C11.316
2C1-C61.399
3C6-C51.380
4C5-C71.404
5C7-C81.369
6C8-N61.320
Table
Table 3. Absorption and emission characteristics of selected merocyanines 5 and 8 and cyanines 6 (recorded in CH2Cl2 at T = 293 K).
Table 3. Absorption and emission characteristics of selected merocyanines 5 and 8 and cyanines 6 (recorded in CH2Cl2 at T = 293 K).
EntryCompoundλmax,abs [nm] a (ε [M−1cm−1])λmax,em [nm] bStokes Shift Δ ν ~ [cm−1] c
1 Photochem 02 00044 i0015a373 (71,000)n.d. d
2 Photochem 02 00044 i0025b373 (71,000)n.d. d
3 Photochem 02 00044 i0035c365 (19,000)n.d. d
4 Photochem 02 00044 i0045d383 (22,000)n.d. d
5 Photochem 02 00044 i0055e388 (43,000)n.d. d
6 Photochem 02 00044 i0068442 (27,000)n.d. d
7 Photochem 02 00044 i0076b443 (114,000)459800
8 Photochem 02 00044 i0086c459 (130,000)5132300
a Longest wavelength absorption maximum. b Emission maximum. c Δ ν ~ = 1/λmax,abs – 1/λmax,em [cm−1]. d Not detected.
Table
Table 4. Experimentally determined longest wavelength absorption band (recorded in dichloromethane at T = 298 K) and TDDFT calculated absorption spectra of merocyanine 5b using various functionals and 6-311++G** as a basis set.
Table 4. Experimentally determined longest wavelength absorption band (recorded in dichloromethane at T = 298 K) and TDDFT calculated absorption spectra of merocyanine 5b using various functionals and 6-311++G** as a basis set.
Photochem 02 00044 i0095bλmax,abs exp 373 nm/3.327 eV (71,000 M 1cm 1)
FunctionalStateλmax,abs calcdOscillatoryMost DominantΔEcalcd—exp
[nm][eV]Strength fContribution (%)[eV]
B3LYP aS1361.03.4260.0077HOMO-1→LUMO (92%)
HOMO→LUMO (2%)
S2331.83.7270.6853HOMO→LUMO (97%)
HOMO-1→LUMO (2%)		0.400
S3302.64.0870.0137HOMO→LUMO+1 (97%)
S4272.34.5420.002HOMO→LUMO+2 (91%)
HOMO→LUMO+3 (5%)
S5264.54.6760.004HOMO→LUMO+3 (83%)
HOMO→LUMO+2 (5%)
S6257.94.7960.0157HOMO→LUMO+4 (93%)
HOMO→LUMO+3 (4%)
B3LYP (CH2Cl2) bS1358.13.4540.8517HOMO→LUMO (99%)0.127
S2336.13.6800.0094HOMO-1→LUMO (95%)
S3280.84.4050.0128HOMO→LUMO+1 (96%)
HOMO→LUMO+5 (3%)
S4261.24.7360.0059HOMO→LUMO+2 (97%)
S5253.24.8840.0033HOMO→LUMO+3 (67%)
HOMO→LUMO+4 (28%)
S6247.15.0060.0366HOMO→LUMO+4 (64%)
HOMO→LUMO+3 (26%)
B3LYP (CH2Cl2) cS1345.03.6030.7163HOMO→LUMO (94%)
HOMO-1→LUMO (5%)		0.276
S2334.83.6940.0522HOMO-1→LUMO (90%)
HOMO→LUMO (6%)
S3280.34.4120.0101HOMO→LUMO+1 (96%)
HOMO→LUMO+5 (3%)
S4261.84.7230.0056HOMO→LUMO+2 (97%)
S5253.34.8830.003HOMO→LUMO+3 (61%)
HOMO→LUMO+4 (35%)
S6247.05.0080.0355HOMO→LUMO+4 (58%)
HOMO→LUMO+3 (32%)
PBEh1PBE aS1351.13.5230.0063HOMO-1→LUMO (91%)
HOMO-1→LUMO+2 (5%)
S2315.33.9230.7332HOMO→LUMO (98%)
HOMO-1→LUMO (2%)		ß.596
S3230.75.3610.0137HOMO→LUMO+1 (97%)
S4222.05.5700.0063HOMO-2→LUMO (53%)
HOMO→LUMO+2 (44%)
S5211.45.8490.0049HOMO-1→LUMO+2 (70%)
HOMO-1→LUMO (6%)
S6211.35.8540.0093HOMO→LUMO+4 (82%)
HOMO→LUMO+3 (10%)
PBEh1PBE (CH2Cl2) bS1351.53.5180.8573HOMO→LUMO (99%)0.191
S2326.33.7910.0079HOMO-1→LUMO (93%)
S3268.04.6160.0139HOMO→LUMO+1 (95%)
HOMO→LUMO+5 (4%)
S4247.44.9980.0103HOMO→LUMO+2 (93%)
S5243.35.0840.0044HOMO→LUMO+3 (76%)
HOMO→LUMO+4 (18%)
S6237.75.2040.0374HOMO→LUMO+4 (72%)
HOMO→LUMO+3 (16%)
CAM-B3LYP aS1318.43.8840.0261HOMO-1→LUMO (78%)
HOMO-1→LUMO+2 (6%)
S2301.54.1020.6999HOMO→LUMO (93%)
HOMO-1→LUMO (5%)		0.775
S3212.35.8250.0179HOMO→LUMO+1 (86%)
HOMO→LUMO+6 (7%)
S4204.26.0580.0063HOMO→LUMO+4 (69%)
HOMO→LUMO+2 (11%)
S5198.76.2250.1157HOMO-2→LUMO (86%)
HOMO→LUMO+4 (6%)
S6197.96.2500.0379HOMO→LUMO+2 (55%)
HOMO→LUMO+3 (19%)
CAM-B3LYP (CH2Cl2) bS1343.23.6040.8438HOMO→LUMO (98%)0.277
S2298.14.1490.0024HOMO-1→LUMO (80%)
HOMO-1→LUMO+8 (4%)
S3256.54.8220.016HOMO→LUMO+1 (77%)
HOMO→LUMO+5 (12%)
S4234.15.2820.0084HOMO→LUMO+3 (77%)
HOMO→LUMO+9 (8%)
S5229.05.4010.0358HOMO→LUMO+2 (48%)
HOMO→LUMO+4 (21%)
S6224.95.4980.0206HOMO→LUMO+4 (56%)
HOMO→LUMO+2 (26%)
a Gas phase calculation in absence of PCM. b Employing PCM for dichloromethane as a dielectric continuum. c Employing a state specific solvation for dichloromethane as a dielectric continuum.
Table
Table 5. Experimentally determined longest wavelength absorption band (recorded in dichloromethane at T = 298 K) and TDDFT calculated absorption spectra of cyanine 6b using various functionals and 6-311++G** as a basis set.
Table 5. Experimentally determined longest wavelength absorption band (recorded in dichloromethane at T = 298 K) and TDDFT calculated absorption spectra of cyanine 6b using various functionals and 6-311++G** as a basis set.
Photochem 02 00044 i0106bλmax,abs exp 443 nm/2.801 eV (114,000 M 1cm 1)
FunctionalStateλmax,abs calcdOscillatoryMost DominantΔEcalcd—exp
[nm][eV]Strength fContribution (%)[eV]
B3LYP aS1362.23.4150.9478HOMO→LUMO (100%)0.614
S2250.84.9310.1102HOMO-1→LUMO (76%)
HOMO→LUMO+1 (22%)
S3224.75.5030.0268HOMO-3→LUMO (55%)
HOMO-2→LUMO (28%)
S4223.15.5430.0803HOMO→LUMO+1 (45%)
HOMO-2→LUMO (34%)
S5219.65.6320.0075HOMO→LUMO+2 (88%)
HOMO→LUMO+4 (4%)
S6215.75.7340.0184HOMO-4→LUMO (77%)
HOMO-2→LUMO (12%)
B3LYP (CH2Cl2) bS1386.13.2031.0034HOMO→LUMO (100%)0.402
S2261.34.7340.0031HOMO→LUMO+1 (95%)
S3254.34.8640.1198HOMO-1→LUMO (61%)
HOMO→LUMO+2 (35%)
S4244.45.0610.0263HOMO→LUMO+3 (63%)
HOMO→LUMO+2 (27%)
S5239.25.1710.036HOMO→LUMO+4 64%)
HOMO→LUMO+2 (12%)
S6233.75.2920.1408HOMO→LUMO+4 (26%)
HOMO→LUMO+3 (22%)
B3LYP (CH2Cl2) cS1369.03.3570.8976HOMO→LUMO (100%)0.556
S2261.24.7350.0025HOMO→LUMO+1 (95%)
S3253.54.8790.1085HOMO-1→LUMO (57%)
HOMO→LUMO+2 (39%)
S4244.25.0650.0193HOMO→LUMO+3 (68%)
HOMO→LUMO+2 (24%)
S5239.25.1700.0135HOMO→LUMO+4 (76%)
HOMO→LUMO+2 (6%)
S6231.85.3350.0975HOMO→LUMO+2 (20%)
HOMO→LUMO+3 (20%)
PBEh1PBE aS1357.53.4600.9557HOMO→LUMO (100%)0.659
S2242.75.0960.1278HOMO-1→LUMO (81%)
HOMO→LUMO+1 (18%)
S3219.45.6380.0861HOMO→LUMO+1 (45%)
HOMO-3→LUMO (39%)
S4218.05.6730.0435HOMO-2→LUMO (47%)
HOMO→LUMO+1 (26%)
S5210.55.8750.0024HOMO→LUMO+2 (88%)
HOMO→LUMO+4 (5%)
S6209.65.9020.0174HOMO-4→LUMO (79%)
HOMO-2→LUMO (14%)
PBEh1PBE (CH2Cl2) bS1380.43.2521.0153HOMO→LUMO (99%)0.451
S2250.24.9440.0056HOMO→LUMO+1 (93%)
S3245.65.0360.1362HOMO-1→LUMO (66%)
HOMO→LUMO+2 (30%)
S4233.55.2970.0846HOMO→LUMO+2 (53%)
HOMO→LUMO+3 (26%)
S5230.75.3600.0853HOMO→LUMO+3 (49%)
HOMO→LUMO+4 (23%)
S6226.55.4610.0575HOMO→LUMO+4 (65%)
HOMO→LUMO+3 (18%)
CAM-B3LYP aS1354.73.4870.9695HOMO→LUMO (98%)0.686
S2220.55.6100.2421HOMO-1→LUMO (94%)
S3209.15.9140.0763HOMO→LUMO+1 (96%)
S4202.96.0960.003HOMO→LUMO+2 (73%)
HOMO→LUMO+4 (14%)
S5201.06.1520.0013HOMO-3→LUMO (49%)
HOMO-2→LUMO (35%)
S6189.36.5350.0022HOMO-4→LUMO (83%)
HOMO-3→LUMO (3%)
CAM-B3LYP (CH2Cl2) bS1377.43.2771.0218HOMO→LUMO (98%)
HOMO→LUMO+1 (78%)		0.476
S2239.95.1550.0013HOMO→LUMO+5 (7%)
S3226.35.4650.2191HOMO-1→LUMO (30%)
HOMO→LUMO+4 (17%)
S4221.55.5840.1968HOMO-1→LUMO (64%)
HOMO→LUMO+4 (9%)
S5219.75.6300.0256HOMO→LUMO+3 (45%)
HOMO→LUMO+2 (25%)
S6213.95.7810.0197HOMO→LUMO+2 (38%)
HOMO→LUMO+3 (16%)
a Gas phase calculation in absence of PCM. b Employing PCM for dichloromethane as a dielectric continuum. c Employing a state specific solvation for dichloromethane as a dielectric continuum.
Table
Table 6. Experimental details of the consecutive three-component synthesis of merocyanines 5 and 8 with potassium carbonate as a base.
Table 6. Experimental details of the consecutive three-component synthesis of merocyanines 5 and 8 with potassium carbonate as a base.
EntryAlkyne 3Amine 4 or Fischer’s Base (7)Yield of Merocyanines 5 and 8
1 a140 μL (1.00 mmol) of 3a90 μL (1.0 mmol) of 4a135 mg (65%) of 5a
2 b140 μL (1.00 mmol) of 3a90 μL (1.0 mmol) of 4a82 mg (35%) of 5a
3 a140 μL (1.00 mmol) of 3a85 μL (1.0 mmol) of 4c71 mg (53%) of 5b
4 a110 μL (1.00 mmol) of 3d90 μL (1.0 mmol) of 4a171 mg (55%) of 5c
5 b110 μL (1.00 mmol) of 3d90 μL (1.0 mmol) of 4a212 mg (68%) of 5c
6 a110 μL (1.00 mmol) of 3d100 μL (1.00 mmol) of 4b191 mg (62%) of 5d
7 b110 μL (1.00 mmol) of 3d100 μL (1.00 mmol) of 4b62 mg (20%) of 5d
8 a110 μL (1.00 mmol) of 3d85 μL (1.0 mmol) of 4c118 mg (40%) of 5e
9 b140 µL (1.00 mmol) of 3a180 µL (1.00 mmol) of 1,3,3-trimethyl-2-methylenindoline (7)21 mg (7%) of 8
a The reaction was performed with K2CO3 as a base. b The reaction was performed with NEt3 as a base.
Table
Table 7. Experimental details of the consecutive pseudo four-component synthesis of cyanines 6.
Table 7. Experimental details of the consecutive pseudo four-component synthesis of cyanines 6.
EntryAlkyne 7Amine 9cYield a
1140 µL (0.98 mmol) of 7a85 µL (1.00 mmol) of 9c209 mg (99%) of 6b
2110 µL (1.00 mmol) of 7d85 µL (1.00 mmol) of 9c214 mg (86%) of 6c
a The yield refers to the employed amount of amine, i.e., two equivs of amine 9c reacted with one equiv of compound 2. The unreacted alkyne intermediate was not isolated.
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Papadopoulos, J.; Gerlach, T.; Reiss, G.J.; Mayer, B.; Müller, T.J.J. Consecutive Multicomponent Coupling-Addition Synthesis and Chromophore Characteristics of Cyclohexene-Embedded Merocyanines and Cyanines. Photochem 2022, 2, 672-693. https://doi.org/10.3390/photochem2030044

AMA Style

Papadopoulos J, Gerlach T, Reiss GJ, Mayer B, Müller TJJ. Consecutive Multicomponent Coupling-Addition Synthesis and Chromophore Characteristics of Cyclohexene-Embedded Merocyanines and Cyanines. Photochem. 2022; 2(3):672-693. https://doi.org/10.3390/photochem2030044

Chicago/Turabian Style

Papadopoulos, Julian, Tabea Gerlach, Guido J. Reiss, Bernhard Mayer, and Thomas J. J. Müller. 2022. "Consecutive Multicomponent Coupling-Addition Synthesis and Chromophore Characteristics of Cyclohexene-Embedded Merocyanines and Cyanines" Photochem 2, no. 3: 672-693. https://doi.org/10.3390/photochem2030044

APA Style

Papadopoulos, J., Gerlach, T., Reiss, G. J., Mayer, B., & Müller, T. J. J. (2022). Consecutive Multicomponent Coupling-Addition Synthesis and Chromophore Characteristics of Cyclohexene-Embedded Merocyanines and Cyanines. Photochem, 2(3), 672-693. https://doi.org/10.3390/photochem2030044

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