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Article

Multicomponent Synthesis of New Fluorescent Boron Complexes Derived from 3-Hydroxy-1-phenyl-1H-pyrazole-4-carbaldehyde

by
Viktorija Savickienė
1,
Aurimas Bieliauskas
2,
Sergey Belyakov
3,
Eglė Arbačiauskienė
1,* and
Algirdas Šačkus
2,*
1
Department of Organic Chemistry, Kaunas University of Technology, Radvilėnų pl. 19, LT-50254 Kaunas, Lithuania
2
Institute of Synthetic Chemistry, Kaunas University of Technology, K. Baršausko g. 59, LT-51423 Kaunas, Lithuania
3
Latvian Institute of Organic Synthesis, Aizkraukles 21, LV-1006 Riga, Latvia
*
Authors to whom correspondence should be addressed.
Molecules 2024, 29(14), 3432; https://doi.org/10.3390/molecules29143432
Submission received: 28 June 2024 / Revised: 18 July 2024 / Accepted: 19 July 2024 / Published: 22 July 2024
(This article belongs to the Special Issue Advances in Functional Organic Dye Chemistry)
Browse Figures
Versions Notes

Abstract

:
Novel fluorescent pyrazole-containing boron (III) complexes were synthesized employing a one-pot three-component reaction of 3-hydroxy-1-phenyl-1H-pyrazole-4-carbaldehyde, 2-aminobenzenecarboxylic acids, and boronic acids. The structures of the novel heterocyclic compounds were confirmed using 1H-, 13C-, 15N-, 19F-, and 11B-NMR, IR spectroscopy, HRMS, and single-crystal X-ray diffraction data. The photophysical properties of the obtained iminoboronates were investigated using spectroscopic techniques, such as UV–vis and fluorescence spectroscopies. Compounds display main UV–vis absorption maxima in the blue region, and fluorescence emission maxima are observed in the green region of the visible spectrum. It was revealed that compounds exhibit fluorescence quantum yield up to 4.3% in different solvents and demonstrate an aggregation-induced emission enhancement effect in mixed THF–water solutions.

Graphical Abstract

1. Introduction

Heterocyclic systems possessing a pyrazole ring have found diverse applications in various fields, including pharmaceuticals [1,2], agrochemicals [3,4], and functional materials [5,6]. Among other heterocycles, pyrazole-ring-containing compounds often exhibit anticancer [7,8], anti-inflammatory [9], and antidiabetic activities [10]. Moreover, it is a common structural motif in a variety of drug substances. Anti-inflammatory celecoxib [11], antipsychotic 3-cyano-N-(1,3-diphenyl-1H-pyrazol-5-yl)benzamide (CDPPB) [12], antiobesity rimonabant [13], and analgesic difenamizole [14] can be highlighted as notable examples. Investigations toward agrochemical compounds have also led to the discovery of pyrazole-containing fungicides [15], insecticides [16], and herbicides [17]. In material sciences, pyrazole compounds have emerged as chemosensors [18], biological imaging agents [19], and metal–organic frameworks (MOFs) [20].
Over the years, many methods have been used to synthesize pyrazole derivatives, including ring formation via the cyclocondensation of hydrazines, with carbonyl systems and dipolar cycloadditions being the most relevant [21,22]. Another approach to synthesizing pyrazole derivatives is related to the functionalization of pyrazole ring, and a number of reported synthetic late-stage pyrazole functionalizations rely on (pseudo)halogenation and following transition-metal catalysis or direct C-H functionalization [23,24]. A multicomponent reaction (MCR) approach has also been successfully applied to synthesize pyrazole-containing heterocyclic systems [25,26]. Multicomponent reactions can be highlighted as one of the most valuable tools used by researchers to synthesize heterocyclic compounds, as they meet the principles of sustainable chemistry, are cost- and time-effective, and are atom- and bond-economic [27,28]. Recent examples of multicomponent reactions for synthesizing pyrazole-containing compounds include the synthesis of biheterocyclic pyrazole-linked thiazole or imidazole derivatives from appropriate aryl glyoxal, aryl thioamide, and pyrazolones [29] or the formation of stable pyrazole amides via a Ugi four-component reaction [30]. A multicomponent synthesis approach was applied to obtain multisubstituted pyrazole derivatives from alkynes, nitriles, and titanium imido complexes [31]. We have also reported the synthesis and structural elucidation of several series of novel biheterocyclic pyrazole-containing compounds by employing different types of multicomponent reactions, starting from 3-alkoxy-1H-pyrazole-4-carbaldehydes [32].
The boron (III)-containing complexes, especially the tetracoordinated species, have emerged as organic fluorophores. The boron-dipyrromethene (BODIPY) family of dyes have proved their superior characteristics as they exhibit excellent optical properties, are compatible with a wide range of reaction conditions, easy to functionalize, stable as solids and solutions [33,34,35,36]. The wide application of BODIPY dyes includes cell imaging [37,38], photodynamic therapy [39,40,41], metal ion detection [42,43]. As one of the alternatives for the BODIPYs, also the condensed complexes of boronic acids and salicylidenehydrazones (BASHYs) have been reported [44,45,46,47,48,49,50,51]. Compounds display low luminescence in organic solvents but demonstrate a remarkable aggregation-induced emission enhancement (AIEE) effect. BASHYs have been widely investigated and proven to be interesting as highly fluorescent dyes [44,46,51] or multivalent cancer-cell-targeting drug conjugates [47,48]. However, the synthesis and investigation of boron complexes using heterocyclic carbaldehydes with carbaldehyde moiety adjacent to the hydroxy group instead of salicylic counterparts is still limited.
In continuation of our interest in synthesizing and investigating the properties of various pyrazole derivatives [52,53,54,55,56,57], herein, we report an efficient one-pot multicomponent synthesis of novel pyrazole ring-containing iminoboronates, starting from 3-hydroxy-1-phenyl-1H-pyrazole-4-carbaldehyde, and investigate the photophysical properties of the obtained boronic compounds.

2. Results and Discussion

2.1. Chemistry

The synthesis of iminoboronates is usually achieved via a one-pot, three-component reaction of salicylaldehydes and anthranilic acids condensing to corresponding imines and double condensation with boronic acids. The reaction requires no catalyst, and usually, target products are formed while refluxing the reaction mixture in methanol [45], ethanol [46], acetonitrile [44,47,48], carbon tetrachloride [49], or water [50] media.
The synthesis of the pyrazole-containing organoboron compounds 4a–k was accomplished by starting from 3-hydroxy-1-phenyl-1H-pyrazole-4-carbaldehyde (1) [58], 2-aminobenzenecarboxylic acids (2a–c), and boronic acids (3a–d), and employing an MCR approach (Scheme 1). Refluxing the reaction mixture in ethanol for 48 h, cooling, filtrating, and washing the formed solid provided the target products 4a–k. Efforts to obtain a higher yields by stirring the reaction mixture under MW irradiation [45] or switching the reaction solvent to methanol [47], acetonitrile [44,47,48], or carbon tetrachloride [49] did not improve the results. The scope of the reaction was evaluated using 2-aminobenzenecarboxylic acids substituted with 5-chloro or 5-methyl moieties as well as a variety of boronic acids containing both electron-donating (methyl, methoxy) and electron-withdrawing (fluoro, trifluoromethyl) substituents. The substituents of the reacting materials did not influence the result of the reaction outcome, and the products were formed in a 47–72% yield. All the compounds were obtained as yellow solids stable at ambient conditions. Attempts to obtain an analogous boron complex by employing 4-(diethylamino)phenylboronic acid were unsuccessful, as only unreacted starting materials could be observed in the reaction mixture. The complexes bore a chiral boron center and were obtained as a racemic mixture [45].

2.2. NMR Spectroscopic Investigations

The structure of compounds 4a–k was unambiguously assigned based on the HRMS, IR, and NMR spectral data analysis. We have carried out detailed NMR studies for the obtained novel compounds to fully map 1H, 13C, 15N, 19F, and 11B signals. A detailed analysis of the representative compound 4a is given in Figure 1a–c. The formation of the N → B coordination bond was evidenced via NMR spectroscopy. The 11B NMR spectrum of 4a displays one broad resonance signal at δ 6.1 ppm, which agrees with the data of other tetracoordinated boron-atom-bearing Schiff bases [44,47]. In addition, the remaining key information for structure elucidation was obtained using two-dimensional NMR spectroscopy techniques such as 1H-1H ROESY, 1H-13C HMBC, 1H-13C H2BC, 1H-15N HMBC, and 1,1-ADEQUATE (Figure 1c). For instance, the most downfield methine proton in the 1H NMR spectrum (singlet, δ 9.65 ppm) was assigned to the new (–CH=N+–) bond from the iminoboronate moiety, while another distinct methine signal (singlet, δ 9.24 ppm) was assigned to the pyrazole 5-H proton from the 1H-pyrazol-4-yl moiety.
An unambiguous assignment of the aforementioned methine protons was easily achieved from the long-range HMBC correlation data. The pyrazole 5-H proton solely showed 1H-15N HMBC correlations with the neighboring N-1 “pyrrole-like” (δ −168.9 ppm) and N-2 “pyridine-like” (δ −117.9 ppm) nitrogen atoms. While the methine proton from the iminoboronate moiety correlated with the neighboring nitrogen atom (δ −194.3 ppm) only. These findings were further supported by the distinct long-range 1H-15N HMBC and 1H-13C HMBC correlations between the methine protons (phenyl 2′(6′)-H and 3‴-H) from the neighboring aryl moieties and the corresponding carbon or nitrogen atoms.
The 1H-1H ROESY spectrum of 4a further elucidated the connectivities based on through-space correlations. For example, distinct ROEs were observed between the pyrazole ring proton 5-H, the phenyl group 2′(6′)-H protons (δ 7.92–7.95 ppm), and the most downfield methine proton from the iminoboronate moiety. The aforementioned methine proton also correlated with the 3‴-H proton (δ 8.12 ppm), confirming their proximity in space. Having successfully identified all the main 1H spin systems, the remaining protonated and quaternary carbons were easily assigned from the 1H-13C H2BC and 1,1-ADEQUATE spectral data.
The newly formed iminoboronates 4a–k, which contain a pyrazole ring, consist of three nitrogen atoms. The chemical shifts of the N-1 “pyrrole-like” and N-2 “pyridine-like” nitrogen atoms from the 1H-pyrazol-4-yl moiety were in the ranges from δ −168.0 to −169.3 ppm and from δ −117.3 to −117.9 ppm, respectively. The nitrogen atom in compounds 4a–d,f–h, from the iminoboronate moiety (–CH=N+–), resonated from δ −192.9 to −194.3 ppm, while in the case of compounds 4e,i–k, which contained 4″-CF3 or 5‴-Cl groups, it resonated slightly upfield in the range from δ −196.8 to −197.9 ppm. The 11B NMR spectra of 4a–k exhibited a single broad resonance signal in the range of δ 5.6 to 6.5 ppm. Data analysis showed that the chemical shift values were highly consistent within compounds 4a–k, thus validating the shifts for each position.

2.3. Single-Crystal X-ray Diffraction Analysis

Suitable crystals of 4a for X-ray diffraction analysis were obtained from tetrahydrofuran. The asymmetric unit of 4a contains two independent molecules, A and B (Figure 2), that are connected to each other via a pseudoinversion center, the coordinates of which, although close to the crystallographic point (¾, ¼, ¼), are still different from it (the real coordinates are 0.7250, 0.2508, and 0.2698). Therefore, it is not possible to increase the symmetry of the crystal structure. Thus, this structure belongs to the triclinic crystal system. The configuration of the asymmetric boron atoms in molecules A and B are S- and R-, respectively. Thus, the substance represents a true racemate.
The heterocyclic system is almost planar; only one boron atom deviates from the plane of the remaining atoms of this system (the deviations are 0.573(7) Å for A and 0.588(7) Å for B). The plane of the phenyl substituent in position 10 makes a dihedral angle with the plane of the heterocycle equal to 17.3(4)° (in A) and 16.1(4)° (in B). The phenyl ring in position 7 is perpendicular to the heterocycle; the dihedral angles are 89.7(4)° in A and 88.8(4)° in B.
There is only a slight π–π interaction between molecules A and B, with the shortest atom–atom contact being 3.330(6) Å (between N10 and C13). At the same time, molecule A forms a strong π–π stacking interaction with the neighboring molecule A in the crystal structure. The distance between the least-squares planes of the heterocyclic systems equals 3.159(6) Å. In turn, the B molecule in the crystal of the compound also binds to the neighboring B molecule through the π–π stacking interaction; in this case, the distance between the least-squares planes of the heterocyclic systems equals 3.278(6) Å. Figure 3 illustrates molecular packing in the unit cell.

2.4. Optical Investigations

The UV–vis absorption spectra of compounds 4a–k were first recorded in THF (Figure 4a, Table 1, entries 1–11). The compounds possess the main absorption band in the visible region, at 397–404 nm, and two less intense bands are present in the ultraviolet range, at 309–315 and 258–262 nm. The substituents attached at various positions of the organoboron compounds 4a–k have a negligible effect on the position of the absorption bands.
The fluorescence emissions of compounds 4a–k were first recorded in THF (Figure 4b, Table 1, entries 1–11). The emission maxima are observed at 531–543 nm, and the Stokes shifts are in a range of 128–142 nm. Again, different substituents in the molecular structure of compounds 4a–k do not influence the positions of emission maxima. 4″,5‴-Dimethyl-substituted compound 4g, and 5‴-chloro-substituted analogues 4i–k, however, show slightly batochromic shifts compared to the other compounds. The dyes display a low quantum yield, ranging from 0.1 to 4.3%, which is in accordance with previously reported observations of similar boron complexes [44]. As iminoboronates are known to possess an AIEE effect [45], we further recorded the emission spectra of compounds 4a–k in mixed THF–water solutions with different water contents (0–90%). As shown in Figure 5a–c, the emission intensity and quantum yield (2.7%) of compound 4a are lower in the pure THF solution. As the water fraction increases to 80%, the emission intensity increases, and the quantum yield reaches the maximum value of 26.2%, which is about 10-fold that in the pure THF solution. Further increases in the water fraction has a negative effect on the quantum yield. This observation is in agreement with the AIEE phenomenon: when water is added, the compound precipitates, forming regular particles, which leads to enhanced fluorescence intensity and amorphous particles, thus leading to decreased fluorescence intensity [59]. Compounds 4b–k displayed similar behavior (Figures S1–S10).
The optical properties of compound 4a were further investigated in additional solvents, such as polar protic (MeOH) and polar aprotic (ACN and DMF). As can be observed from UV–vis spectroscopy data, the absorption bands of compound 4a are slightly blue-shifted in more polar solvents (MeOH, ACN, DMF) in comparison to THF (Table 1, entries 12–14, Figure 4a). Fluorescence emissions of compound 4a in MeOH, ACN and DMF possess maxima at 531 nm, and the Stokes shifts are 140, 141, and 138 nm, respectively, which are slightly larger comparing to one in THF solution (133 nm) (Table 1, entry 1, Figure 4b). Compound 4a displays low quantum yields of 3.1, 1.6, and 1.5 in MeOH, ACN, and DMF, respectively (Table 1, entries 12–14).

3. Materials and Methods

3.1. General

All the starting materials were purchased from commercial suppliers and used as received. Flash column chromatography was performed on silica gel (60 Å; 230–400 µm; supplied by Sigma-Aldrich; Merck KGaA, Darmstadt, Germany). The reaction progress was monitored by TLC analysis on Macherey-Nagel™ ALUGRAM® Xtra SIL G/UV254 plates (Macherey-Nagel GmbH & Co. KG, Düren, Germany) which were visualized by UV light (254 and 365 nm wavelengths).
Melting points were determined on a Büchi M-565 melting point apparatus and were not corrected. IR spectra of neat samples were recorded on a Bruker Vertex 70v FT-IR spectrometer (Bruker Optik GmbH, Ettlingen, Germany), and the results were reported as the frequency of absorption (cm−1). Mass spectra were obtained using a Shimadzu LCMS-2020 (ESI+) spectrometer (Shimadzu Corporation, Kyoto, Japan). High-resolution mass spectra were measured on a Bruker MicrOTOF-Q III (ESI+) apparatus (Bruker Daltonik GmbH, Bremen, Germany).
1H, 13C and 15N NMR spectra were recorded in DMSO-d6 solutions at 25 °C on a Bruker Avance III 700 (700 MHz for 1H, 176 MHz for 13C, and 71 MHz for 15N) spectrometer (Bruker BioSpin GmbH, Rheinstetten, Germany) equipped with a 5-mm TCI 1H-13C/15N/D z-gradient cryoprobe. The chemical shifts (δ), were expressed relative to tetramethylsilane (TMS) in ppm. The 15N NMR spectra were referenced to neat, external nitromethane (using a coaxial capillary). 19F NMR spectra (376 MHz) and 11B NMR spectra (128 MHz) were obtained on a Bruker Avance III 400 instrument (Bruker BioSpin AG, Faellanden, Switzerland); with an absolute referencing via Ξ ratio was used. The 1H, 13C and 15N NMR resonances were completely and unambiguously assigned using a combination of standard NMR spectroscopic techniques [60], including DEPT, COSY, TOCSY, ROESY, NOESY, gs-HSQC, gs-HMBC, H2BC, LR-HSQMBC and 1,1-ADEQUATE [61].
Single crystals were investigated at 160 K on a Rigaku, XtaLAB Synergy, Dualflex, HyPix diffractometer (Rigaku Corporation, Tokyo, Japan) using monochromated Cu-Kα radiation (λ = 1.54184 Å). The crystal structure of 4a was solved by direct methods [62] and refined by full-matrix least squares [63]. All nonhydrogen atoms were refined in anisotropical approximation. Hydrogen atoms were refined by riding model with Uiso(H) = 1.2Ueq(C). Crystal data for 4a: triclinic: a = 8.0614(2), b = 14.5439(5), c = 16.3846(7) Å, α = 87.613(3)°, β = 77.887(3)°, γ = 80.845(3)°; V = 1854.2(1) Å3, Z = 4, μ = 0.766 mm−1, Dcalc = 1.408 g·cm−3; space group is P 1 ¯ . For further details, see crystallographic data for 4a deposited at the Cambridge Crystallographic Data Centre as Supplementary Publications Number CCDC 2313164. Copies of the data can be obtained, free of charge, on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK.
The UV–vis spectra were recorded on a Shimadzu 2600 UV/vis (Shimadzu Corporation, Japan). The fluorescence spectra were recorded on an FL920 fluorescence spectrometer from Edinburgh Instruments (Edinburgh Analytical Instruments Limited, Edinburgh, UK). The PL quantum yields were measured from dilute solutions by an absolute method using the Edinburgh Instruments integrating sphere excited with a Xe lamp. It was ensured that the optical densities of the sample solutions were below 0.1 to avoid reabsorption effects. All the optical measurements were performed at room temperature under ambient conditions.
The following abbreviation is used in reporting the NMR data: Pz, pyrazole. The 1H, 13C, and 11B NMR spectra, as well as the HRMS data of the new compounds, are provided in Figures S11–S56 of the Supplementary Materials.

3.2. Synthetic Procedures

General procedure for the compound 4a–k synthesis:
To a mixture of 3-hydroxy-1-phenyl-1H-pyrazole-4-carbaldehyde (1) (188 mg, 1 mmol) in EtOH (5 mL), appropriate anthranilic acid 2 (1 mmol) and phenylboronic acid 3 (1 mmol) were added. The reaction mixture was stirred at 70 °C for 48 h. After completing the reaction, as determined via TLC, the reaction mixture was cooled to room temperature. Then, the reaction mixture was filtered, and the obtained solid was washed with ethanol and acetone to acquire pure products 4a–k.
[2-({[3-(hydroxy-κO)-1-phenyl-1H-pyrazol-4-yl]methylidene}amino-κN)benzoato(2-)-κO](phenyl)boron (4a). Yellow solid; yield 72% (282 mg); m.p. 324–325 °C. IR (vmax, cm−1): 3127 (CHarom.), 1696, 1627, 1582, 1404 (C=O, C=N, C=C), 1175, 1026 (C–O), 758, 686 (C=C benzene). 1H NMR (700 MHz, DMSO-d6): δH ppm 7.09–7.14 (m, 3H, 3″,4″,5″-H), 7.18–7.22 (m, 2H, 2″,6″-H), 7.41 (t, J = 7.31 Hz, m, 1H, 4′-H), 7.50–7.53 (m, 1H, 5‴-H), 7.54–7.57 (m, 2H, 3′,5′-H), 7.78–7.81 (m, 1H, 4‴-H), 7.92–7.95 (m, 2H, 2′,6′-H), 8.00 (dd, J = 7.8, 1.5 Hz, 1H, 6‴-H), 8.12 (d, J = 8.1 Hz, 1H, 3‴-H), 9.24 (s, 1H, 5-H), 9.65 (s, 1H, CHN). 13C NMR (176 MHz, DMSO-d6): δC ppm 104.8 (C-4), 119.5 (C-2′,6′), 119.9 (C-3‴), 123.4 (C-1‴), 127.9 (C-3″,5″), 128.0 (C-4″), 128.3 (C-4′), 129.2 (C-5‴), 130.1 (C-3′,5′), 130.6 (C-2″,6″), 131.0 (C-6‴), 132.7 (C-5), 135.1 (C-4‴), 138.8 (C-1′), 140.8 (C-2‴), 144.4 (C-1″), 156.6 (CHN), 162.0 (COO), 162.8 (C-3). 15N NMR (71 MHz, DMSO-d6): δN ppm −117.9 (Pz N-2), −168.9 (Pz N-1), −194.3 (N+). 11B NMR (128 MHz, DMSO-d6): δB ppm 6.1 (B). HRMS (ESI+) for C23H16BN3NaO3 ([M + Na]+) calcd 416.1181, found 416.1183.
[2-({[3-(hydroxy-κO)-1-phenyl-1H-pyrazol-4-yl]methylidene}amino-κN)benzoato(2-)-κO](4-methylphenyl)boron (4b). Yellow solid; yield 63% (257 mg); m.p. 333–334 °C. IR (vmax, cm−1): 3126, 3069 (CHarom.), 1693, 1631, 1588, 1494, 1405 (C=O, C=N, C=C), 1164, 1021 (C–O), 754, 730, 683 (C=C of benzene). 1H NMR (700 MHz, DMSO-d6): δH ppm 2.04 (s, 3H, 4″-CH3), 6.83 (d, J = 7.8 Hz, 2H, 3″,5″-H), 6.97 (d, J = 7.8 Hz, 2H, 2″,6″-H), 7.31–7.35 (m, 1H, 4′-H), 7.43–7.49 (m, 3H, 3′,5′,5‴-H), 7.69–7.74 (m, 1H, 4‴-H), 7.87–7.89 (m, 3H, 2′,6′,6‴-H), 8.15 (d, J = 8.2 Hz, 1H, 3‴-H), 9.35 (s, 1H, 5-H), 9.86 (s, 1H, CHN). 13C NMR (176 MHz, DMSO-d6): δC ppm 21.1 (4″-CH3), 104.6 (C-4), 119.2 (C-2′,6′), 119.8 (C-3‴), 123.0 (C-1‴), 128.1 (C-4′), 128.4 (C-3″,5″), 129.0 (C-5‴), 130.0 (C-3′,5′), 130.4 (C-2″,6″), 130.7 (C-6‴), 133.1 (C-5), 135.0 (C-4‴), 136.7 (C-4″), 138.6 (C-1′), 140.5 (C-2‴), 140.8 (C-1″), 156.6 (CHN), 161.9 (COO), 162.6 (C-3). 15N NMR (71 MHz, DMSO-d6): δN ppm −117.8 (Pz N-2), −168.7 (Pz N-1), −193.8 (N+). 11B NMR (128 MHz, DMSO-d6): δB ppm 6.2 (B). HRMS (ESI+) for C24H18BN3NaO3 ([M + Na]+) calcd 430.1338, found 430.1338.
[2-({[3-(hydroxy-κO)-1-phenyl-1H-pyrazol-4-yl]methylidene}amino-κN)benzoato(2-)-κO](4-methoxyphenyl)boron (4c). Yellow solid; yield 54% (220 mg); m.p. 323–324 °C. IR (vmax, cm−1): 3129 (CHarom.), 1695, 1631, 1601, 1583, 1497 (C=O, C=N, C=C), 1163, 1020 (C–O), 753, 732, 682 (C=C of benzene). 1H NMR (700 MHz, DMSO-d6): δH ppm 3.52 (s, 3H, 4″-OCH3) 6.57–7.62 (m, 2H, 3″,5″-H), 6.95–7.01 (m, 2H, 2″,6″-H), 7.30–7.35 (m, 1H, 4′-H), 7.44–7.48 (m, 3H, 3′,5′,5‴-H), 7.71–7.73 (m, 1H, 4‴-H), 7.87–7.89 (m, 3H, 2′,6′,6‴-H), 8.16 (d, J = 8.2 Hz, 1H, 3‴-H), 9.35 (s, 1H, 5-H), 9.86 (s, 1H, CHN). 13C NMR (176 MHz, DMSO-d6): δC ppm 55.1 (4″-OCH3), 104.6 (C-4), 113.3 (C-3″, 5″), 119.2 (C-2′,6′), 119.8 (C-3‴), 123.0 (C-1‴), 128.1 (C-4′), 129.0 (C-5‴), 130.0 (C-3′, 5′), 130.7 (C-6‴), 131.7 (C-2″,6″), 133.0 (C-5), 135.0 (C-4‴), 135.6 (C-1″), 138.6 (C-1′), 140.5 (C-2‴), 156.5 (CHN), 159.01 (C-4″), 161.9 (COO), 162.6 (C-3). 15N NMR (71 MHz, DMSO-d6): δN ppm −168.9 (Pz N-1), −193.8 (N+), Pz N-2 was not found. 11B NMR (128 MHz, DMSO-d6): δB ppm 6.3 (B). HRMS (ESI+) for C24H18BN3NaO4 ([M + Na]+) calcd 446.1287, found 446.1292.
(4-fluorophenyl)[2-({[3-(hydroxy-κO)-1-phenyl-1H-pyrazol-4-yl]methylidene}amino-κN)benzoato(2-)-κO]boron (4d). Yellow solid; yield 47% (194 mg); m.p. 318–319 °C. IR (vmax, cm−1): 3129, 3073 (CHarom.), 1696, 1629, 1582, 1405 (C=O, C=N, C=C), 1171, 1027 (C–O), 759, 731, 687 (C=C of benzene). 1H NMR (700 MHz, DMSO-d6): δH ppm 6.92–6.96 (m, 2H, 3″,5″-H), 7.20–7.24 (m, 2H, 2″,6″-H), 7.39–7.43 (m, 1H, 4′-H), 7.5–7.53 (m, 1H, 5‴-H), 7.54–7.56 (m, 2H, 3′,5′-H), 7.78–7.81 (m, 1H, 4‴-H), 7.91–7.92 (m, 2H, 2′,6′-H), 8.01 (dd, J = 7.8, 1.5 Hz, 1H, 6‴-H), 8.08 (d, J = 8.2 Hz, 1H, 3‴-H), 9.20 (s, 1H, 5-H), 9.56 (s, 1H, CHN). 13C NMR (176 MHz, DMSO-d6): δC ppm 104.2 (C-4), 114.3 (d, J = 19.6 Hz, C-3″,5″), 119.1 (C-2′,6′), 119.4 (C-3‴), 122.9 (C-1‴), 127.9 (C-4′), 128.7 (C-5‴), 129.7 (C-3′,5′), 130.5 (C-6‴), 132.19 (C-5), 132.19 (d, J = 14.4 Hz, C-2″,6″), 134.7 (C-4‴), 138.4 (C-1′), 140.0 (C-1″), 140.2 (C-2‴), 156.3 (CHN), 161.4 (COO), 162.0 (d, J = 243.2 Hz, C-4″), 162.2 (C-3). 15N NMR (71 MHz, DMSO-d6): δN ppm −117.3 (Pz N-2), −168.1 (Pz N-1), −194.3 (N+). 19F NMR (376 MHz, DMSO-d6): δN ppm −114.5 (F). 11B NMR (128 MHz, DMSO-d6): δB ppm 5.8 (B). HRMS (ESI+) for C23H15BFN3NaO3 ([M + Na]+) calcd 434.1087, found 434.1085.
[2-({[3-(hydroxy-κO)-1-phenyl-1H-pyrazol-4-yl]methylidene}amino-κN)benzoato(2-)-κO][4-(trifluoromethyl)phenyl]boron (4e). Yellow solid; yield 58% (267 mg); m.p. 323–324 °C. IR (vmax, cm−1): 3131, 3075 (CHarom.), 1696, 1627, 1583, 1499, 1407 (C=O, C=N, C=C), 1326, 1295, 1174, 1108 (C–O, C–F), 802, 756, 730, 683 (C=C of benzene). 1H NMR (700 MHz, DMSO-d6): δH ppm 7.31–7.34 (m, 3H, 4′,2″,6″-H), 7.38–7.39 (m, 2H, 3″,5″-H), 7.44–7.49 (m, 3H, 3′,5′,5‴-H), 7.72–7.76 (m, 1H, 4‴-H), 7.86–7.90 (m, 2H, 2′,6′,6‴-H), 8.21 (d, J = 8.2 Hz, 1H, 3‴-H), 9.41 (s, 1H, 5-H), 9.91 (s, 1H, CHN). 13C NMR (176 MHz, DMSO-d6): δC ppm 104.5 (C-4), 119.3 (C-2′,6′), 120.0 (C-3‴), 122.3 (C-1‴), 124.4 (q, J = 3.9 Hz, C-3″,5″), 124.6 (q, J = 272.3 Hz, 4″-CF3), 128.1 (C-4′), 128.3 (q, J = 31.4 Hz, C-4″), 129.1 (C-5‴), 130.0 (C-3′,5′), 130.7 (C-6‴), 131.1 (C-2″,6″), 133.3 (C-5), 135.2 (C-4‴), 138.5 (C-1′), 140.3 (C-2‴), 149.3 (C-1″), 157.4 (CHN), 161.6 (COO), 162.3 (C-3). 15N NMR (71 MHz, DMSO-d6): δN ppm −117.6 (Pz N-2), −168.2 (Pz N-1), −196.9 (N+). 19F NMR (376 MHz, DMSO-d6): δN ppm −61.0 (CF3). 11B NMR (128 MHz, DMSO-d6): δB ppm 5.6 (B). HRMS (ESI+) for C24H15BF3N3NaO3 ([M + Na]+) calcd 484.1055, found 484.1059.
[2-({[3-(hydroxy-κO)-1-phenyl-1H-pyrazol-4-yl]methylidene}amino-κN)-5-methylbenzoato(2-)-κO](phenyl)boron (4f). Yellow solid; yield 50% (204 mg); m.p. 342–343 °C. IR (vmax, cm−1): 3126, 3055 (CHarom.), 1691, 1626, 1587, 1488, 1403 (C=O, C=N, C=C), 1175. 1021 (C–O), 864, 754, 732 (C=C of benzene). 1H NMR (700 MHz, DMSO-d6): δH ppm 2.33 (s, 3H, 5‴-CH3), 7.05–7.10 (m, 3H, 3″,4″,5″-H), 7.14–7.16 (m, 2H, 2″,6″-H), 7.35–7.39 (m, 1H, 4′-H), 7.49–7.53 (m, 2H, 3′,5′-H), 7.57 (dd, J = 8.5, 2.1 Hz, 1H, 4‴-H), 7.76 (d, J = 2.0 Hz, 1H, 6‴-H), 7.89–7.92 (m, 2H, 2′,6′-H), 8.03 (d, J = 8.8 Hz, 1H, 3‴-H), 9.27 (s, 1H, 5-H), 9.71 (s, 1H, CHN). 13C NMR (176 MHz, DMSO-d6): δC ppm 20.6 (5‴-CH3), 104.4 (C-4), 119.0 (C-2′,6′), 119.3 (C-3‴), 122.6 (C-1‴), 127.5 (C-3″,4″,5″), 127.8 (C-4′), 129.7 (C-3′,5′), 130.2 (C-2″,6″), 130.6 (C-6‴), 132.3 (C-5), 135.4 (C-4‴), 138.0 (C-2‴), 138.5 (C-1′), 138.8 (C-5‴), 144.0 (C-1″), 155.5 (CHN), 161.7 (COO), 162.3 (C-3). 15N NMR (71 MHz, DMSO-d6): δN ppm −117.5 (Pz N-2), −169.0 (Pz N-1), −193.4 (N+). 11B NMR (128 MHz, DMSO-d6): δB ppm 5.8 (B). HRMS (ESI+) for C24H18BN3NaO3 ([M + Na]+) calcd 430.1338, found 430.1340.
[2-({[3-(hydroxy-κO)-1-phenyl-1H-pyrazol-4-yl]methylidene}amino-κN)-5-methylbenzoato(2-)-κO](4-methylphenyl)boron (4g). Yellow solid; yield 59% (249 mg); m.p. 339–340 °C. IR (vmax, cm−1): 3086, 3039 (CHarom.), 1698, 1624, 1589, 1488, 1404 (C=O, C=N, C=C), 1218, 1167, 1038 (C–O), 785, 752, 732, 684 (C=C of benzene). 1H NMR (700 MHz, DMSO-d6): δH ppm 2.04 (s, 3H, 4″-CH3), 2.28 (s, 3H, 5‴-CH3), 6.83 (d, J = 7.8 Hz, 2H, 3″,5″-H), 6.93–6.98 (m, 2H, 2″,6″-H), 7.29–7.35 (m, 1H, 4′-H), 7.42–7.49 (m, 2H, 3′,5′-H), 7.52 (dd, J = 8.7, 2.1 Hz, 1H, 4‴-H), 7.67 (d, J = 2.0 Hz, 1H, 6‴-H), 7.84–7.89 (m, 2H, 2′,6′-H), 8.02 (d, J = 8.4 Hz, 1H, 3‴-H), 9.32 (s, 1H, 5-H), 9.81 (s, 1H, CHN). 13C NMR (176 MHz, DMSO-d6): δC ppm 20.8 (5‴-CH3), 21.1 (4″-CH3), 104.5 (C-4), 119.2 (C-2′,6′), 119.6 (C-3‴), 122.7 (C-1‴), 128.0 (C-4′), 128.4 (C-3″,5″), 130.0 (C-3′,5′), 130.4 (C-2″,6″), 130.7 (C-6‴), 132.8 (C-5), 135.6 (C-4‴), 136.7 (C-4″), 138.2 (C-2‴), 138.6 (C-1′), 138.9 (C-5‴), 140.9 (C-1″), 155.8 (CHN), 162.0 (COO), 162.5 (C-3). 15N NMR (71 MHz, DMSO-d6): δN ppm −169.3 (Pz N-1), −193.2 (N+), Pz N-2 was not found. 11B NMR (128 MHz, DMSO-d6): δB ppm 6.3 (B). HRMS (ESI+) for C25H20BN3NaO3 ([M + Na]+) calcd 444.1494, found 444.1495.
[2-({[3-(hydroxy-κO)-1-phenyl-1H-pyrazol-4-yl]methylidene}amino-κN)-5-methylbenzoato(2-)-κO](4-methoxyphenyl)boron (4h). Yellow solid; yield 56% (245 mg); m.p. 330–331 °C. IR (vmax, cm−1): 3126, 3037 (CHarom.), 1694, 1631, 1588, 1494, 1406 (C=O, C=N, C=C), 1165, 1021 (C–O), 863, 795, 754, 730, 684 (C=C of benzene). 1H NMR (700 MHz, DMSO-d6): δH ppm 2.28 (s, 3H, 5‴-CH3), 3.52 (s, 3H, 4″-OCH3), 6.56–6.63 (m, 2H, 3″,5″-H), 6.95–7.01 (m, 2H, 2″,6″-H), 7.31–7.35 (m, 1H, 4′-H), 7.45–7.49 (m, 2H, 3′,5′-H), 7.53 (dd, J = 8.6, 2.0 Hz, 1H, 4‴-H), 7.68 (d, J = 2.0 Hz, 1H, 6‴-H), 7.84–7.88 (m, 2H, 2′,6′-H), 8.03 (d, J = 8.4 Hz, 1H, 3‴-H), 9.32 (s, 1H, 5-H), 9.81 (s, 1H, CHN). 13C NMR (176 MHz, DMSO-d6): δC ppm 20.8 (5‴-CH3), 55.1 (4″-OCH3), 104.5 (C-4), 113.3 (C-3″,5″), 119.2 (C-2′,6′), 119.6 (C-3‴), 122.7 (C-1‴), 128.0 (C-4′), 130.0 (C-3′,5′), 130.7 (C-6‴), 131.6 (C-2″,6″), 132.8 (C-5), 135.6 (C-4‴), 135.8 (C-1″), 138.2 (C-2‴), 138.6 (C-1′), 138.9 (C-5‴), 155.7 (CHN), 159.0 (C-4″), 162.0 (COO), 162.6 (C-3). 15N NMR (71 MHz, DMSO-d6): δN ppm −169.3 (Pz N-1), −192.9 (N+), Pz N-2 was not found. 11B NMR (128 MHz, DMSO-d6): δB ppm 5.9 (B). HRMS (ESI+) for C25H20BN3NaO4 ([M + Na]+) calcd 460.1444, found 460.1447.
[5-chloro-2-({[3-(hydroxy-κO)-1-phenyl-1H-pyrazol-4-yl]methylidene}amino-κN)benzoato(2-)-κO](phenyl)boron (4i). Yellow solid; yield 71% (303 mg); m.p. 365–366 °C. IR (vmax, cm−1): 3082 (CHarom.), 1700, 1623, 1589, 1497, 1472, 1400 (C=O, C=N, C=C), 1179, 1021 (C–O), 776, 752, 688, 643 (C=C of benzene, C–Cl). 1H NMR (700 MHz, DMSO-d6): δH ppm 7.05–7.10 (m, 3H, 3″,4″,5″-H), 7.12–7.16 (m, 2H, 2″,6″-H), 7.35–7.39 (m, 1H, 4′-H), 7.48–7.53 (m, 2H, 3′,5′-H), 7.83–7.87 (m, 2H, 4‴,6‴-H), 7.89–7.93 (m, 2H, 2′,6′-H), 8.25–8.28 (m, 1H, 3‴-H), 9.37 (s, 1H, 5-H), 9.82 (s, 1H, CHN). 13C NMR (176 MHz, DMSO-d6): δC ppm 104.5 (C-4), 119.2 (C-2′,6′), 122.1 (C-3‴), 124.4 (C-1‴), 127.7 (C-3″,5″), 127.8 (C-4″), 128.0 (C-4′), 129.7 (C-6‴), 129.8 (C-3′,5′), 130.3 (C-2″,6″), 132.99 (C-5), 133.01 (C-5‴), 134.6 (C-4‴), 138.4 (C-1′), 139.4 (C-2‴), 143.6 (C-1″), 157.1 (CHN), 160.6 (COO), 162.4 (C-3). 15N NMR (71 MHz, DMSO-d6): δN ppm −117.4 (Pz N-2), −168.0 (Pz N-1), −197.5 (N+). 11B NMR (128 MHz, DMSO-d6): δB ppm 5.9 (B). HRMS (ESI+) for C23H15BClN3NaO3 ([M + Na]+) calcd 450.0791, found 450.0794.
[5-chloro-2-({[3-(hydroxy-κO)-1-phenyl-1H-pyrazol-4-yl]methylidene}amino-κN)benzoato(2-)-κO](4-methylphenyl)boron (4j). Yellow solid; yield 55% (243 mg); m.p. 364–365 °C. IR (vmax, cm−1): 3105, 3085 (CHarom.), 1701, 1617, 1587, 1497, 1469, 1400 (C=O, C=N, C=C), 1206, 1172, 1035 (C–O), 856, 772, 748, 679 (C=C of benzene, C–Cl). 1H NMR (700 MHz, DMSO-d6): δH ppm 2.05 (s, 3H, 4″-CH3), 6.84 (d, J = 7.8 Hz, 2H, 3″,5″-H), 6.97 (d, J = 7.9 Hz, 2H, 2″,6″-H), 7.32–7.36 (m, 1H, 4′-H), 7.45–7.49 (m, 2H, 3′,5′-H), 7.79 (d, 1H, J = 2.5 Hz, 6‴-H), 7.81 (dd, J = 8.6, 2.6 Hz, 1H, 4‴-H), 7.86–7.90 (m, 2H, 2′,6′-H), 8.25 (d, J = 8.7 Hz, 1H, 3‴-H), 9.39 (s, 1H, 5-H), 9.85 (s, 1H, CHN). 13C NMR (176 MHz, DMSO-d6): δC ppm 21.1 (4″-CH3), 104.6 (C-4), 119.3 (C-2′,6′), 122.3 (C-3‴), 124.5 (C-1‴), 128.2 (C-4′), 128.4 (C-3″,5″), 129.7 (C-6‴), 130.0 (C-3′,5′), 130.4 (C-2″,6″), 133.0 (C-5), 133.3 (C-5‴), 134.7 (C-4‴), 136.9 (C-4″), 138.5 (C-1′), 139.5 (C-2‴), 140.7 (C-1″), 157.2 (CHN), 160.8 (COO), 162.5 (C-3). 15N NMR (71 MHz, DMSO-d6): δN ppm, −168.6 (Pz N-1), −197.9 (N+), Pz N-2 was not found. 11B NMR (128 MHz, DMSO-d6): δB ppm 6.5 (B). HRMS (ESI+) for C24H17BClN3NaO4 ([M + Na]+) calcd 464.0948, found 464.0952.
[5-chloro-2-({[3-(hydroxy-κO)-1-phenyl-1H-pyrazol-4-yl]methylidene}amino-κN)benzoato(2-)-κO](4-methoxyphenyl)boron (4k). Yellow solid; yield 48% (220 mg); m.p. 333–334 °C. IR (vmax, cm−1): 3128, 3040 (CHarom.), 1694, 1633, 1591, 1477, 1405(C=O, C=N, C=C), 1182, 1010 (C–O), 861, 754, 728, 669 (C=C of benzene, C–Cl). 1H NMR (700 MHz, DMSO-d6): δH ppm 3.55 (s, 3H, 4″-OCH3), 6.58–6.66 (m, 2H, 3″,5″-H), 7.98–7.04 (m, 2H, 2″,6″-H), 7.34–7.36 (m, 1H, 4′-H), 7.46–7.53 (m, 2H, 3′,5′-H), 7.81–7.86 (m, 2H, 4‴,6‴-H), 7.88–7.92 (m, 2H, 2′,6′-H), 8.23–8.27 (m, 1H, 3‴-H), 9.37 (s, 1H, 5-H), 9.83 (s, 1H, CHN). 13C NMR (176 MHz, DMSO-d6): δC ppm 55.0 (4″-OCH3), 104.6 (C-4), 113.3 (C-3″,5″), 119.2 (C-2′,6′), 122.2 (C-3‴), 124.5 (C-1‴), 128.1 (C-4′), 129.7 (C-6‴), 129.9 (C-3′,5′), 131.7 (C-2″,6″), 133.0 (C-5), 133.1 (C-5‴), 134.7 (C-4‴), 135.2 (C-1″), 138.5 (C-1′), 139.5 (C-2‴), 156.9 (CHN), 159.1 (C-4″), 160.8 (COO), 162.5 (C-3). 15N NMR (71 MHz, DMSO-d6): δN ppm −117.8 (Pz N-2), −168.0 (Pz N-1), −196.8 (N+). 11B NMR (128 MHz, DMSO-d6): δB ppm 6.2 (B). HRMS (ESI+) for C24H17BClN3NaO4 ([M + Na]+) calcd 480.0897, found 480.0898.

4. Conclusions

In conclusion, a series of novel pyrazole-containing boron (III) complexes were synthesized from 3-hydroxy-1-phenyl-1H-pyrazole-4-carbaldehyde, 2-aminobenzene-carboxylic acids, and boronic acids via a one-pot multicomponent reaction, achieving good yields. The novel compounds were characterized via IR and advanced NMR spectroscopies as well as HRMS data. Additionally, X-ray single crystal analysis showed the presence of an asymmetric boron center and two enantiomers in each unit cell of crystals. The photophysical properties of the obtained compounds were investigated in different solvents. The compounds were faintly luminescent in THF, MeOH, ACN, and DMF solutions, and demonstrated aggregation-induced emission enhancement in mixed THF–water solutions. These compounds can be further investigated as luminescent materials or probes.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/molecules29143432/s1, Figures S1–S10: Fluorescence emission spectra of compounds 4b–4k in mixed THF–water solutions. Figures S11–S56: 1H, 13C, 19F 11B NMR and HRMS (ESI) spectra of compounds 4a–k.

Author Contributions

Conceptualization, A.Š.; methodology, A.Š. and E.A.; formal analysis, A.Š. and E.A.; investigation, V.S., S.B. and A.B.; resources, A.Š. and E.A.; data curation, A.Š., V.S., A.B. and E.A.; writing—original draft preparation, A.Š., E.A., V.S. and A.B.; writing—review and editing, A.Š. and E.A.; visualization, A.Š. and A.B.; supervision, E.A. and A.Š.; funding acquisition, A.Š. and E.A. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Research Council of Lithuania (No. S-MIP-23-51).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data are contained within the article and Supplementary Materials.

Conflicts of Interest

The authors declare no conflict of interest.

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Molecules 29 03432 sch001
Scheme 1. Synthesis of compounds 4a–k. Reagents and conditions: EtOH, 70 °C, 48 h.
Scheme 1. Synthesis of compounds 4a–k. Reagents and conditions: EtOH, 70 °C, 48 h.
Molecules 29 03432 sch001
Molecules 29 03432 g001
Figure 1. (a) 1H NMR (italics) and 15N NMR (bold) chemical shifts [ppm, ref. TMS (1H) and CH3NO2 (15N)] of compound 4a in DMSO-d6; (b) 13C NMR (regular) and 11B NMR (underlined) chemical shifts [ppm; ref. TMS] of compound 4a in DMSO-d6; (c) relevant 1,1-ADEQUATE, 1H-13C HMBC, 1H-15N HMBC, 1H-13C H2BC, and ROE correlations.
Figure 1. (a) 1H NMR (italics) and 15N NMR (bold) chemical shifts [ppm, ref. TMS (1H) and CH3NO2 (15N)] of compound 4a in DMSO-d6; (b) 13C NMR (regular) and 11B NMR (underlined) chemical shifts [ppm; ref. TMS] of compound 4a in DMSO-d6; (c) relevant 1,1-ADEQUATE, 1H-13C HMBC, 1H-15N HMBC, 1H-13C H2BC, and ROE correlations.
Molecules 29 03432 g001
Molecules 29 03432 g002
Figure 2. ORTEP diagram of structure 4a with bond lengths characterizing the tetrahedron of boron (molecules A and B are connected to each other via a pseudoinversion center).
Figure 2. ORTEP diagram of structure 4a with bond lengths characterizing the tetrahedron of boron (molecules A and B are connected to each other via a pseudoinversion center).
Molecules 29 03432 g002
Molecules 29 03432 g003
Figure 3. Molecular packing in crystal structure 4a. Both molecules A (as well as molecules B) are connected by a crystallographic center of inversion; molecules B and A are connected by a pseudoinversion center.
Figure 3. Molecular packing in crystal structure 4a. Both molecules A (as well as molecules B) are connected by a crystallographic center of inversion; molecules B and A are connected by a pseudoinversion center.
Molecules 29 03432 g003
Molecules 29 03432 g004
Figure 4. (a) UV–vis absorption spectra of compounds 4a–k in different solvents: a THF, b MeOH, c ACN, and d DMF; (b) fluorescence emission spectra (λex = 400 nm) of compounds 4a–h in different solvents: a THF, b MeOH, c ACN, and d DMF.
Figure 4. (a) UV–vis absorption spectra of compounds 4a–k in different solvents: a THF, b MeOH, c ACN, and d DMF; (b) fluorescence emission spectra (λex = 400 nm) of compounds 4a–h in different solvents: a THF, b MeOH, c ACN, and d DMF.
Molecules 29 03432 g004
Molecules 29 03432 g005
Figure 5. (a) Fluorescence emission spectra (λex = 440 nm) of compound 4a in mixed THF–water solutions with different water fractions (0–90%); (b) the relationship between the quantum yield of 4a and the water fraction in mixed THF–water solutions; (c) fluorescence photograph of compound 4a in THF (left) and mixed THF–water (20/80) solution (right) under 365 nm wavelength UV light.
Figure 5. (a) Fluorescence emission spectra (λex = 440 nm) of compound 4a in mixed THF–water solutions with different water fractions (0–90%); (b) the relationship between the quantum yield of 4a and the water fraction in mixed THF–water solutions; (c) fluorescence photograph of compound 4a in THF (left) and mixed THF–water (20/80) solution (right) under 365 nm wavelength UV light.
Molecules 29 03432 g005
Table 1. Absorption (λabs of absorption maxima and ε), fluorescence emission (λem), and quantum yield (Φf) parameters and Stokes shifts for 4a–k in different solvents: a THF, b MeOH, c ACN, and d DMF (λex = 400 nm) and mixed THF–water solutions (λex = 440 nm).
Table 1. Absorption (λabs of absorption maxima and ε), fluorescence emission (λem), and quantum yield (Φf) parameters and Stokes shifts for 4a–k in different solvents: a THF, b MeOH, c ACN, and d DMF (λex = 400 nm) and mixed THF–water solutions (λex = 440 nm).
EntryComp.λabs
(nm)		ε × 103
(dm3mol−1 cm−1)		λem (nm) Stokes Shifts (nm)Φf (%)λem (nm) in
H2O–THF (v/v %)		Φf (%)
in H2O–THF (v/v %)
14a a26014.68 1332.7524
H2O/THF (80/20)		26.2
H2O/THF
(80/20)
31010.61533
40017.80
24b a26026.07 1322.8526
H2O/THF (70/30)		18.8
H2O/THF
(70/30)
31130.14531
39930.72
34c a26012.02 1350.2529
H2O/THF (90/10)		11.9
H2O/THF
(90/10)
3097.69533
39813.17
44d a25918.56 1371.9544
H2O/THF (80/20)		25.4
H2O/THF
(80/20)
31213.12534
39722.54
54e a26020.58 525
H2O/THF (80/20)		30.6
H2O/THF
(80/20)
31213.685321351.9
39724.65
64f a26111.67 527
H2O/THF (80/20)		15.1
H2O/THF
(80/20)
3127.455291280.4
40114.71
74g a2606.67 546
H2O/THF (80/20)		52.2
H2O/THF
(80/20)
3134.525431422.0
4018.11
84h a26213.01 538
H2O/THF (80/20)		29.2
H2O/THF
(80/20)
3137.805311310.5
40015.00
94i a2586.10 537
H2O/THF (80/20)		7.0
H2O/THF
(80/20)
3154.605381343.7
4047.88
104j a25711.53 536
H2O/THF (80/20)		24.4
H2O/THF
(80/20)
3158.825391354.3
40414.43
114k a25920.80 1350.1539
H2O/THF (80/20)		19.8
H2O/THF
(80/20)
31515.48538
40326.77
124a b25513.46
3057.865311411.6--
39014.10
134a c25720.00
30614.035311403.1--
39125.17
144a d25826.45
30517.535311381.5--
39328.78
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Savickienė, V.; Bieliauskas, A.; Belyakov, S.; Arbačiauskienė, E.; Šačkus, A. Multicomponent Synthesis of New Fluorescent Boron Complexes Derived from 3-Hydroxy-1-phenyl-1H-pyrazole-4-carbaldehyde. Molecules 2024, 29, 3432. https://doi.org/10.3390/molecules29143432

AMA Style

Savickienė V, Bieliauskas A, Belyakov S, Arbačiauskienė E, Šačkus A. Multicomponent Synthesis of New Fluorescent Boron Complexes Derived from 3-Hydroxy-1-phenyl-1H-pyrazole-4-carbaldehyde. Molecules. 2024; 29(14):3432. https://doi.org/10.3390/molecules29143432

Chicago/Turabian Style

Savickienė, Viktorija, Aurimas Bieliauskas, Sergey Belyakov, Eglė Arbačiauskienė, and Algirdas Šačkus. 2024. "Multicomponent Synthesis of New Fluorescent Boron Complexes Derived from 3-Hydroxy-1-phenyl-1H-pyrazole-4-carbaldehyde" Molecules 29, no. 14: 3432. https://doi.org/10.3390/molecules29143432

APA Style

Savickienė, V., Bieliauskas, A., Belyakov, S., Arbačiauskienė, E., & Šačkus, A. (2024). Multicomponent Synthesis of New Fluorescent Boron Complexes Derived from 3-Hydroxy-1-phenyl-1H-pyrazole-4-carbaldehyde. Molecules, 29(14), 3432. https://doi.org/10.3390/molecules29143432

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