An ab initio simulation of a dithienylethene/phenoxynaphthacenequinone photochromic hybrid

Revisiting Peri-Aryloxyquinones: From a Forgotten Photochromic System to a Promising Tool for Emerging Applications

Emerging applications of photochromic compounds demand new molecular designs that can be inspired by some long-known yet currently forgotten classes of photoswitches. In the present review, we remind the community about Peri-AryloxyQuinones (PAQs) and their unique photoswitching behavior originally discovered more than 50 years ago. At the heart of this phenomenon is the light-induced migration of an aromatic moiety (arylotropy) in peri-aryloxy-substituted quinones resulting in ana-quinones. PAQs feature absorbance of both isomers in the visible spectral region, photochromism in the amorphous and crystalline state, and thermal stability of the photogenerated ana-isomer. Particularly noticeable is the high sensitivity of the ana-isomer towards nucleophiles in solution. In addition to the mechanism of molecular photochromism and the underlaying structure-switch relationships, we analyze potential applications and prospects of aryloxyquinones in optically switchable materials and devices. Due to their ability to efficiently photoswitch in the solid state, PAQs are indeed attractive candidates for such materials and devices, including electronics (optically controllable circuits, switches, transistors, memories, and displays), porous crystalline materials, crystalline actuators, photoactivated sensors, and many more. This review is intended to serve as a guide for researchers who wish to use photoswitchable PAQs in the development of new photocontrollable materials, devices, and processes.

Visualization and Comprehension of Electronic and Topographic Contrasts on Cooperatively Switched Diarylethene-Bridged Ditopic Ligand

Diarylethene is a prototypical molecular switch that can be reversibly photoisomerized between its open and closed forms. Ligands bpy-DAE-bpy, consisting of a phenyl-diarylethene-phenyl (DAE) central core and bipyridine (bpy) terminal substituents, are able to self-organize. They are investigated by scanning tunneling microscopy at the solid–liquid interface. Upon light irradiation, cooperative photochromic switching of the ligands is recognized down to the submolecular level. The closed isomers show different electron density of states (DOS) contrasts, attributed to the HOMO or LUMO molecular orbitals observed. More importantly, the LUMO images show remarkable differences between the open and closed isomers, attributed to combined topographic and electronic contrasts mainly on the DAE moieties. The electronic contrasts from multiple HOMO or LUMO distributions, combined with topographic distortion of the open or closed DAE, are interpreted by density functional theory (DFT) calculations.

Photochromic and luminescence properties of a hybrid compound based on indoline spiropyran of the coumarin type and azomethinocoumarin

A novel hybrid compound whose molecule includes the photochromic spiropyran fragment and two fluorophores - coumarin and salicylideneimine - was synthesized by the reaction of two equivalents of 8-formyl-7-hydroxy-4-methylcoumarin with 5-amino-1,3,3-trimethyl-2-methyleneindoline. Its spectral-kinetic and fluorescence properties were studied in comparison with model compounds - 7-hydroxy-4-methyl-coumarin, spiropyran of the coumarin type, and azomethinocoumarin in toluene and ethanol. It was shown that the hybrid compound exhibited photochromic transformations in both solvents. Different fluorescence emissions of the initial spirocycle and UV irradiation-induced merocyanine forms were observed. One green fluorescence emission with a maximum at 545 nm was observed for the initial closed form in toluene, and several emissions with maxima at 390 nm, 440 nm, 450 nm (violet), and 530 nm (green) appeared in ethanol. An additional red emission of the open merocyanine form in the region of 665 nm appeared after UV irradiation in both solvents. Reversible modulation of fluorescence in both the initial and photoinduced merocyanine forms in the process of photochromic transformations was discovered. It was shown that the fluorescence modulation of the hybrid compound in weakly polar toluene was caused by resonance energy transfer from the fluorescent fragment of the photochromic compound to the photoinduced merocyanine form, leading to the process of photochromic transformations. Reversible modulation of fluorescence in ethanol solutions was achieved through a photoinduced change in the ratio of the concentrations of conformers.

Multiphotochromic molecular systems

We review molecular compounds encompassing several photochromic units with a focus on their functionalities.

Diarylethene-dihydroazulene multimode photochrome: a theoretical spectroscopic investigation

Using Time-Dependent Density Functional Theory, we have assessed the structural, energetic and spectroscopic properties of a hybrid diarylethene-dihydroazulene multi-addressable switch synthesized by Mrozek et al. [Chem. Commun., 1999, 1487-1488]. All possible closed/open structures have been considered and the different activation barriers along each reaction path have been evaluated. The determination of the energetic profiles allowed us to pinpoint the thermally possible reactions. To simulate the electronic absorption spectra of this compact two-way four-state hybrid compound, we relied on a PCM-TD-DFT approach combined with a molecular orbital analysis. Key insights are reached and the experimental photochromic properties of this multi-component switch are rationalised. From a more methodological point of view, this work also shows that range-separated hybrid functionals (CAM-B3LYP and ωB97XD) allow to reproduce the measured spectroscopic features with a remarkable accuracy.