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Photoswitchable Materials
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Photoswitchable Materials

A special issue of Materials (ISSN 1996-1944).

Deadline for manuscript submissions: closed (30 July 2017) | Viewed by 17931

Special Issue Editor

Prof. Dr. Vance Williams

E-Mail Website
Guest Editor
Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada
Interests: organic synthesis; liquid crystals; conjugated polymers; gels; self-assembly; molecular recognition; electronic materials; photochromism; novel aromatic systems
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Although the phenomenon of photochromism was discovered more than a century ago, it is only within the last two decades that the study of molecular photoswitches has attracted serious attention. The ability to toggle molecular and macroscopic properties continues to be exploited both in solution and the solid state, and for applications that range from the modulation of biological processes to information and energy storage. The ongoing importance of these systems was recently highlighted by the 2016 Nobel Prize for Chemistry, awarded to Ben Feringa for his work on photoswitches and their use in molecular machines.

It is within the field of material science that photoswitches realize their true potential. Changes at the molecular level that accompany switching processes have been used to create dynamic materials whose macroscopic optical, electronic and morphological properties can be reversibly altered using light. This Special Issue is dedicated to work at the frontier of research into advanced materials that exploit the unique opportunities presented by these photoactive building blocks.

Dr. Vance Williams
Guest Editor

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Keywords

  • molecular switches
  • photoswitches
  • photochromism
  • photochemistry

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Published Papers (3 papers)

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Research

2253 KiB  
Article
Phenylazopyridine as Switch in Photochemical Reactions. A Detailed Computational Description of the Mechanism of Its Photoisomerization
by Josep Casellas, Gerard Alcover-Fortuny, Coen De Graaf and Mar Reguero
Materials 2017, 10(12), 1342; https://doi.org/10.3390/ma10121342 - 23 Nov 2017
Cited by 17 | Viewed by 6013
Abstract
Azo compounds are organic photochromic systems that have the possibility of switching between cis and trans isomers under irradiation. The different photochemical properties of these isomers make azo compounds into good light-triggered switches, and their significantly different geometries make them very interesting as [...] Read more.
Azo compounds are organic photochromic systems that have the possibility of switching between cis and trans isomers under irradiation. The different photochemical properties of these isomers make azo compounds into good light-triggered switches, and their significantly different geometries make them very interesting as components in molecular engines or mechanical switches. For instance, azo ligands are used in coordination complexes to trigger photoresponsive properties. The light-induced trans-to-cis isomerization of phenylazopyridine (PAPy) plays a fundamental role in the room-temperature switchable spin crossover of Ni-porphyrin derivatives. In this work, we present a computational study developed at the SA-CASSCF/CASPT2 level (State Averaged Complete Active Space Self Consistent Field/CAS second order Perturbation Theory) to elucidate the mechanism, up to now unknown, of the cis–trans photoisomerization of 3-PAPy. We have analyzed the possible reaction pathways along its lowest excited states, generated by excitation of one or two electrons from the lone pairs of the N atoms of the azo group (nazoπ*2 and nazo2π*2 states), from a π delocalized molecular orbital (ππ* state), or from the lone pair of the N atom of the pyridine moiety (npyπ* state). Our results show that the mechanism proceeds mainly along the rotation coordinate in both the nazoπ* and ππ* excited states, although the nazo2π*2 state can also be populated temporarily, while the npyπ* does not intervene in the reaction. For rotationally constrained systems, accessible paths to reach the cis minimum along planar geometries have also been located, again on the nazoπ* and ππ* potential energy surfaces, while the nazo2π*2 and npyπ* states are not involved in the reaction. The relative energies of the different paths differ from those found for azobenzene in a previous work, so our results predict some differences between the reactivities of both compounds. Full article
(This article belongs to the Special Issue Photoswitchable Materials)
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2122 KiB  
Article
Level of Theory and Solvent Effects on DASA Absorption Properties Prediction: Comparing TD-DFT, CASPT2 and NEVPT2
by Cristina García-Iriepa and Marco Marazzi
Materials 2017, 10(9), 1025; https://doi.org/10.3390/ma10091025 - 3 Sep 2017
Cited by 24 | Viewed by 6270
Abstract
Donor–acceptor Stenhouse adducts (DASAs) are a very recent class of organic photoswitches that combine excellent properties, such as color and polarity change, a large structural modification, and excellent fatigue resistance. Despite their potential applications in different fields, very few studies have focused on [...] Read more.
Donor–acceptor Stenhouse adducts (DASAs) are a very recent class of organic photoswitches that combine excellent properties, such as color and polarity change, a large structural modification, and excellent fatigue resistance. Despite their potential applications in different fields, very few studies have focused on rationalizing their electronic structure properties. Here, by means of different state-of-the-art theoretical methods, including solvent and vibrational effects, we show that while time dependent-density functional theory (TD-DFT) can qualitatively describe DASAs’ excited states, multiconfigurational quantum chemistry methods along with dynamic electron correlation (CASPT2, NEVPT2) are required for a quantitative agreement with the experiment. This finding is reasoned based on the different charge transfer characteristics observed. Moreover, the TD-DFT computed two-photon absorption properties are reported and suggested to red-shift the absorption band, as required for biological applications. Full article
(This article belongs to the Special Issue Photoswitchable Materials)
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2369 KiB  
Article
Photoswitchable Fluorescent Diarylethene Derivatives with Thiophene 1,1-Dioxide Groups: Effect of Alkyl Substituents at the Reactive Carbons
by Masakazu Morimoto, Takaki Sumi and Masahiro Irie
Materials 2017, 10(9), 1021; https://doi.org/10.3390/ma10091021 - 2 Sep 2017
Cited by 14 | Viewed by 5018
Abstract
Photoswitching and fluorescent properties of sulfone derivatives of 1,2-bis(2-alkyl-4-methyl-5-phenyl-3-thienyl)perfluorocyclopentene, 1–5, having methyl, ethyl, n-propyl, i-propyl, and i-butyl substituents at the reactive carbons (2- and 2′-positions) of the thiophene 1,1-dioxide rings were studied. Diarylethenes 1–5 underwent [...] Read more.
Photoswitching and fluorescent properties of sulfone derivatives of 1,2-bis(2-alkyl-4-methyl-5-phenyl-3-thienyl)perfluorocyclopentene, 1–5, having methyl, ethyl, n-propyl, i-propyl, and i-butyl substituents at the reactive carbons (2- and 2′-positions) of the thiophene 1,1-dioxide rings were studied. Diarylethenes 1–5 underwent isomerization reactions between open-ring and closed-ring forms upon alternate irradiation with ultraviolet (UV) and visible light and showed fluorescence in the closed-ring forms. The alkyl substitution at the reactive carbons affects the fluorescent property of the closed-ring isomers. The closed-ring isomers 2b–5b with ethyl, n-propyl, i-propyl, and i-butyl substituents show higher fluorescence quantum yields than 1b with methyl substituents. In polar solvents, the fluorescence quantum yield of 1b markedly decreases, while 2b–5b maintain the relatively high fluorescence quantum yields. Although the cycloreversion quantum yields of the derivatives with methyl, ethyl, n-propyl, and i-propyl substituents are quite low and in the order of 10−5, introduction of i-butyl substituents was found to increase the yield up to the order of 10−3. These results indicate that appropriate alkyl substitution at the reactive carbons is indispensable for properly controlling the photoswitching and fluorescent properties of the photoswitchable fluorescent diarylethenes, which are potentially applicable to super-resolution fluorescence microscopies. Full article
(This article belongs to the Special Issue Photoswitchable Materials)
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