M. Irie et al., Photochromism of 1,2-bis(2-methyl-5-phenyl-3-thienyl)perfluorocyclopentenein a single-crystalline phase, J AM CHEM S, 122(20), 2000, pp. 4871-4876
1,2-Bis(2-methyl-5-phenyl-3-thienyl)perfluorocyclopentene (1a) and their de
rivatives, 1,2-bis(2-methyl-5-p-tolyl-3-thienyl)perfluorocyclopentene (2a)
and 1,2-bis(2-methyl-5-p-tert-butylphenyl-3-thienyl); perfluorocyclopentene
(3a), were found to undergo reversible photochromic reactions in the singl
e-crystalline phase. Upon irradiation with 366 nm light the single crystals
turned blue. The blue colored crystals returned to colorless by irradiatio
n with visible light (lambda > 480 nm). The substituents at para positions
of the phenyl groups did not affect the rates of photocyclization reactions
both in the single-crystalline phase and in hexane. Activation energies of
the photocyclization reactions were almost zero. On the other hand, activa
tion energies as much as 5-10 kJ mol(-1) were observed in the photocyclorev
ersion reactions in the single-crystalline phase. These values were smaller
than those observed in solution, ca. 16 kJ mol(-1) Slow thermal cyclorever
sion reaction of the closed-ring isomer (1b) was observed above 150 degrees
C. The activation energy was 139 kJ mol(-1).