Maria Buthelezi - Thermosolvatochromism of nitrospiropyran and merocyanine free and bound to cyclodextrin

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  J. Phys.   Chem. B, 2012, 116 (8), 2483


  The thermosolvatochromism of nitrospiropyran free and bound to   cyclodextrin was studied in dimethylsulfoxide (DMSO)-water binary   solvent systems. Spiropyran was interconverted to merocyanine by   heating the sample to 55 °C. The merocyanine (MC) was converted   back to spiropyran (SP) either by cooling the sample to room   temperature or irradiating the sample with a visible light   emitting diode. Steady state absorption spectra of SP and MC   samples in the free state and bound to cyclodextrin were obtained   in several DMSO-water binary solutions. Emission spectra of MC   both free and cyclodextrin-bound were also acquired. Blue-shifted   absorption and emission spectra of the studied molecules with   increasing solvent polarity suggest that the dipole moments of   free and bound merocyanines are higher in the ground state   compared to the excited state. Merocyanine dipole moments in the   ground and excited states were determined using   thermosolvatochromism measurements and the Lippert-Mataga,   Bakhshiev, and Kawski-Chamma-Viallet polarity functions. A large   change in the dipole moment (ca. 16 D) of the merocyanine in   aqueous DMSO was obtained upon electronic excitation, S(1) ←   S(0). Analysis of the merocyanine Stokes' shifts as a function of   solvent polarity indicates that both general solvent effects and   specific solvent effects are present in all systems studied.   These findings reveal that merocyanine could be utilized as a   polarity sensor for DMSO-water binary solutions.

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