Fluorescence of Photochromic 1,2-Bis(3-methyl-2-thienyl)ethene

Characteristic fluorescence properties of photochromic 1,2-bis(3-methyl-2-thienyl)perfluorocyclopentene were studied in solution as well as in the single-crystalline phase. When the concentration of 1,2-bis(3-methyl-2-thienyl)perfluorocyclopentene was increased in a 3-methylpentane solution, the fluorescence spectrum showed a bathochromic shift and a new fluorescence excitation peak attributable to intermolecular aggregates was observed in the wavelength region between 350 and 400 nm. Upon irradiation with light shorter than 330 nm, the dithienylethene derivatives underwent a photochromic reaction to produce the closed-ring isomer, while no reaction was observed when excited at 350−400 nm. Similar fluorescence spectra attributable to intermolecular interaction were observed in the spectrum of the single crystal. X-ray crystallographic analysis and polarized fluorescence measurement revealed that the characteristic photochromic reactivity and fluorescence property are controlled by the intermolecular interaction between two neighboring thiophene rings.