TY - JOUR A1 - Titov, Evgenii T1 - On the low-lying electronically excited states of azobenzene dimers BT - Transition density matrix analysis JF - Molecules : a journal of synthetic chemistry and natural product chemistry / Molecular Diversity Preservation International N2 - Azobenzene-containing molecules may associate with each other in systems such as self-assembled monolayers or micelles. The interaction between azobenzene units leads to a formation of exciton states in these molecular assemblies. Apart from local excitations of monomers, the electronic transitions to the exciton states may involve charge transfer excitations. Here, we perform quantum chemical calculations and apply transition density matrix analysis to quantify local and charge transfer contributions to the lowest electronic transitions in azobenzene dimers of various arrangements. We find that the transitions to the lowest exciton states of the considered dimers are dominated by local excitations, but charge transfer contributions become sizable for some of the lowest pi pi* electronic transitions in stacked and slip-stacked dimers at short intermolecular distances. In addition, we assess different ways to partition the transition density matrix between fragments. In particular, we find that the inclusion of the atomic orbital overlap has a pronounced effect on quantifying charge transfer contributions if a large basis set is used. KW - azobenzene KW - dimer KW - transition density matrix KW - exciton KW - charge transfer KW - excited states KW - TD-DFT KW - ADC(2) Y1 - 2021 U6 - https://doi.org/10.3390/molecules26144245 SN - 1420-3049 VL - 26 IS - 14 PB - MDPI CY - Basel ER - TY - JOUR A1 - Titov, Evgenii A1 - Sharma, Anjali A1 - Lomadze, Nino A1 - Saalfrank, Peter A1 - Santer, Svetlana A1 - Bekir, Marek T1 - Photoisomerization of an azobenzene-containing surfactant within a micelle JF - ChemPhotoChem N2 - Photosensitive azobenzene-containing surfactants have attracted great attention in past years because they offer a means to control soft-matter transformations with light. At concentrations higher than the critical micelle concentration (CMC), the surfactant molecules aggregate and form micelles, which leads to a slowdown of the photoinduced trans -> cis azobenzene isomerization. Here, we combine nonadiabatic dynamics simulations for the surfactant molecules embedded in the micelles with absorption spectroscopy measurements of micellar solutions to uncover the reasons responsible for the reaction slowdown. Our simulations reveal a decrease of isomerization quantum yields for molecules inside the micelles. We also observe a reduction of extinction coefficients upon micellization. These findings explain the deceleration of the trans -> cis switching in micelles of the azobenzene-containing surfactants. KW - azobenzene KW - micelles KW - photoswitches KW - rate constants KW - surfactants KW - surface hopping Y1 - 2021 U6 - https://doi.org/10.1002/cptc.202100103 SN - 2367-0932 VL - 5 IS - 10 SP - 926 EP - 932 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Ryabchun, Alexander A1 - Sakhno, Oksana A1 - Stumpe, Joachim A1 - Bobrovsky, Alexey T1 - Full-Polymer Cholesteric Composites for Transmission and Reflection Holographic Gratings JF - Advanced optical materials N2 - A new type of self-organized materials based on cholesteric networks filled with photoactive side-chain copolymer is being developed. Supramolecular helical structure of cholesteric polymer network resulting in the selective reflection is used as a photonic scaffold. Photochromic azobenzene-containing nematic copolymer is embedded in cholesteric scaffold and utilized as a photoactive media for optical pattering. 1D and 2D transmission diffraction gratings are successfully recorded in composite films by holographic technique. For the first time the possibility to create selective reflection gratings in cholesteric material mimicking the natural optical properties of cholesteric mesophase is demonstrated. That enables the coexistence of two selective gratings, where one has an intrinsic cholesteric periodic helical structure and the other is a holographic grating generated in photochromic polymer. The full-polymer composites provide high light-induced optical anisotropy due to effective photo-orientation of side-chain fragments of the azobenzene-containing liquid crystalline polymer, and prevent the degradation of the helical superstructure maintaining all optical properties of cholesteric mesophase. The proposed class of optical materials could be easily applied to a broad range of polymeric materials with specific functionality. The versatility of the adjustment and material preprogramming combined with high optical performance makes these materials a highly promising candidate for modern optical and photonic applications. KW - azobenzene KW - cholesteric scaffolds KW - holography KW - LC polymer KW - polarization diffraction grating KW - reflection grating Y1 - 2017 U6 - https://doi.org/10.1002/adom.201700314 SN - 2195-1071 VL - 5 SP - 376 EP - 379 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Ryabchun, Alexander A1 - Raguzin, Ivan A1 - Stumpe, Joachim A1 - Shibaev, Valery A1 - Bobrovsky, Alexey T1 - Cholesteric Polymer Scaffolds Filled with Azobenzene-Containing Nematic Mixture with Phototunable Optical Properties JF - Scientific reports N2 - The past two decades witnessed tremendous progress in the field of creation of different types of responsive materials. Cholesteric polymer networks present a very promising class of smart materials due to the combination of the unique optical properties of cholesteric mesophase and high mechanical properties of polymer networks. In the present work we demonstrate the possibility of fast and reversible photocontrol of the optical properties of cholesteric polymer networks. Several cholesteric photopolymerizable mixtures are prepared, and porous cholesteric network films with different helix pitches are produced by polymerization of these mixtures. An effective and simple method of the introduction of photochromic azobenzene-containing nematic mixture capable of isothermal photoinducing the nematic isotropic phase transition into the porous polymer matrix is developed, It is found that cross-linking density and degree of polymer network filling with a photochromic nematic mixture strongly influence the photo-optical behavior of the obtained composite films. In particular, the densely cross-linked films are characterized by a decrease in selective light reflection bandwidth, whereas weakly cross-linked systems display two processes: the shift of selective light reflection peak and decrease of its width. It is noteworthy that the obtained cholesteric materials are shown to be very promising for the variety applications in optoelectronics and photonics. KW - liquid crystalline polymer KW - azobenzene KW - cholesteric phase KW - phototunable optical properties KW - selective light reflection KW - LC composites Y1 - 2016 U6 - https://doi.org/10.1021/acsami.6b09642 SN - 1944-8244 VL - 8 SP - 27227 EP - 27235 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Miasnikova, Anna A1 - Benitez-Montoya, Carlos Adrian A1 - Laschewsky, André T1 - Counterintuitive photomodulation of the thermal phase transition of poly(methoxy diethylene glycol acrylate) in aqueous solution by trans-cis isomerization of Copolymerized Azobenzenes JF - Macromolecular chemistry and physics N2 - The non-ionic monomer (methoxy diethylene glycol) acrylate is copolymerized with its azodye-functionalized acrylate analogue using reversible addition-fragmentation chain transfer (RAFT) polymerization. Copolymerization is increasingly difficult with increasing amounts of the azo-dye-bearing monomer. The resulting water-soluble polymers are thermosensitive, exhibiting lower critical solution temperature (LCST) behavior, which can be modulated by the photoinduced trans-cis isomerization of the dye. While already small contents of the hydrophobic azobenzene group reduce the phase-transition temperatures of the copolymers strongly, photoisomerization of the apolar trans-state to the more-polar cis-state has only a small effect, and decreases rather than increases the cloud points. KW - azobenzene KW - photoisomerization KW - statistical copolymers KW - thermoresponsive materials KW - water-soluble polymers Y1 - 2013 U6 - https://doi.org/10.1002/macp.201300203 SN - 1022-1352 VL - 214 IS - 13 SP - 1504 EP - 1514 PB - Wiley-VCH CY - Weinheim ER -