Optical properties of photochromic dyes in the amorphous state

Optical properties of photo chromic dyes, 1,2-bis(2-methylbenzo[b]thiophen-3-yl)perfluorocyclopentene (BFCP) and cis-1,2-dicyano-1,2-bis(2,4,5-trimethyl-3-thienyl)ethene have been studied in the solid state. These photochromic dyes have been found to form a stable amorphous solid state when they are sandwiched between two glass plates. The time for the transition from the amorphous state tb the crystalline state increases with decreasing distance between the two glass plates. The amorphous solid films clearly show photochromism upon light irradiation and also a marked change in photoluminescence intensity. The crystallization of the open-ring BFCP isomer is much faster than that of the closed-ring isomer. It has also been revealed that the photoluminescence spectrum of BFCP changes upon photoisomerization.