Synthesis and photochromic properties of novel yellow developing photochromic compounds

Two 1-thiazolyl-2-thienylcyclopentene derivatives, and , and a 1-thiazolyl-2-vinylcyclopentene derivative have been synthesized in an attempt to obtain photochromic compounds which change the color from colorless to yellow, and have low photocycloreversion quantum yields and high absorption coefficients of the colored isomers. All of these compounds underwent reversible photochromic reactions. Compounds and in toluene solutions changed the color upon 313 nm light irradiation from colorless to orange and pink, in which absorption maxima were observed at 494 nm (ε=10,000 M−1 cm−1) and 525 nm (ε=8500 M−1 cm−1), respectively. On the other hand, the colorless toluene solution of turned yellow upon irradiation with 313 nm light, in which the absorption maximum was observed at 416 nm (ε=17,100 M−1 cm−1). The photocyclization/cycloreversion quantum yields of were 0.19 and 0.0014, respectively. The conversion from the open- to the closed-ring isomer of in the photostationary state under irradiation with 313 nm light was close to 100%.