Isothermal and non-isothermal techniques in kinetic studies of reactions in a photoactive molecular material

The kinetics of thermally driven reactions in a crystalline photochromic so lid, 1-methyl-2,4,4,6-tetraphenyl-1,4-dihydropyridine (DHP), has been studi ed. The processes have been monitored by measuring the isothermal bleaching of coloured species produced upon UV irradiation of DHP, and by measuring the heat flow in non-isothermal differential scanning calorimetry experimen ts. Signatures of two processes were detected; a combination of quantum-che mical calculations and spectroscopic measurements allowed us to attribute t hem to reactions occurring in the photochromic system.