Thermal hysteresis in the photoresponsivity of a langmuir film of amphiphilic spiropyran

We have found a thermal hysteresis in the photoresponsivity of a Langmuir film for the first time. The Langmuir film of an amphiphilic spiropyran, 1',3'-dihydro-3',3'-dimethyl-6-nitro-1'-octadecyl-8-(docosanoyloxymethyl)spiro[2H-1-benzopyran-2,2'-(2H)-indole] (SP) was fabricated at 13 degrees C at 10 mN m-1, followed by heating to a given temperature. UV irradiation of this film caused only the isomerization of SP to the corresponding merocyanine (MC) up to 29 degrees C. Light-induced J-aggregation of MC occurred at 30 degrees C. On the other hand, once the film was heated to 30 degrees C, light-induced J-aggregation was observed down to 27 degrees C. The hysteresis should be related with the phase transitions that occur in the bulk of SP at similar temperatures. No significant morphological change occurred by light-induced J-aggregation in the Langmuir-Blodgett (LB) film of SP by the present method, in contrast to the case of the LB films fabricated under isothermal conditions at 30 degrees C. This feature enabled us to pattern the LB film with J-aggregate of MC by UV irradiation through a photomask of lines with a width of 5 mum each.     

Synthesis and studies of some cholest-5-en-3-ol-(3β)[4-phenylpyridylazo]carbonate-containing supramolecular hydrogen-bonded mesogens

Mesogenic materials containing cholest-5-en-3-ol-(3β)[4-phenylpyridylazo]carbonate (CPPC) and 4-n-alkyloxybenzoic acids have been synthesized using hydrogen bonding as a mechanism for self-assembly. Phase diagrams of the binary mixtures of the hydrogen bond donor and acceptor were established using polarizing optical microscopy. The maximum isotropization point was observed for the 50 mol % composition confirming the formation of stable 1 : 1 complexes due to intermolecular hydrogen bonding. All the supramolecular assemblies built from 1 : 1 molar ratios of the hydrogen bond donor and acceptor moieties exhibit well defined smectic A (SmA) liquid crystal phases on heating and cooling cycles. The SmA phases exhibited by the complexes are not observed for the individual components. The azobenzene moiety of CPPC undergoes trans-cis-photoisomerization with a quantum yield of 0.1 and the activation energy for the thermal cis-trans-isomerization was estimated as 92 kJ mol-¹.     

A quantum-mechanical study of the vinyl fluoride adsorbed on the rutile TiO2(1 1 0) surface

The adsorption of vinyl fluoride on the rutile TiO₂(1 1 0) surface has been simulated, on the basis of a recently proposed experimental model, using hybrid-exchange density functional theory. Different surface coverages have been considered and the lateral interaction between adsorbed vinyl fluoride molecules has been quantified through a simple model of nearest and next nearest neighbouring molecules. The vibrational frequencies of the adsorbed molecule have been calculated and are found to be in excellent agreement with those observed providing support for the proposed adsorption model. The effect of the adsorption on the electronic structure of the molecule and the surface have been characterised by computing electrostatic potential maps and the local density of states.     

Solvent effects in the reaction between (anthracen‐9‐yl)methyl sulfides and electron‐deficient acetylenes

Solvent‐dependent diverse reactivity of (anthracen‐9‐yl)methyl sulfides with a few electron‐deficient acetylenes is described. Diversity in reactivity is attributed to competition between one electron transfer, two electron transfer and Diels–Alder reaction of these sulfides with electron‐deficient acetylenes. We have proposed plausible mechanisms to account for various reactions observed by us. Copyright © 2015 John Wiley & Sons, Ltd.     

Dramatic solvent and concentration dependence in the reaction of (anthracen‐9‐yl)methanamines with suitable electron‐deficient acetylenes

Herein, we describe diverse reactivity of (anthracen‐9‐yl)methanamines with a few electron‐deficient acetylenes. Depending on the solvent and concentration, (anthracen‐9‐yl)methanamines reacted with acetylenes through one electron transfer, two electron transfer, or Diels–Alder pathways; and under certain conditions, we observed multiple reaction pathways. We have proposed plausible mechanisms to account for various reactions observed by us. Copyright © 2014 John Wiley & Sons, Ltd.     

Photoactive dimesogen having different pathways of light driven phase transitions at different temperatures

We hereby describe a novel example of light driven phase transitions in a photoresponsive dimesogen, which goes through different pathways at different temperatures. The isomer ratios required to obtain the phase transition in each case have also been determined.