Photochromism of 10 b, 10 c-Dihydropyrene Derivatives with the t-ButyI Groups at 2,7-Positions

Abstract

Photochromism in 10 b, 10 c-dihydropyrenes possessing the t-butyl groups at 2,7-positions and various substituents at 10 b, 10 c, 4, 5, 9 and 10-positions in Fig. 1 was studied. On each compound, an UV-visible spectrum of stable colored species, the rate constant of a thermal coloration reaction, the quantum yield of a photo-decoloration reaction, and a degradation behavior were investigated. The wavelengths of the absorption maxima of the colored states were summarized in Table 1, and the absorption spectra were compared in Figs. 3 and 4. The rate constants and the activation energies of the thermal coloration were summarized in Table 2 and the Arrhenius plots were shown in Figs. 5-7. The quantum yields of the photo-decoloration were summarized in Table 3. The results were examined in the viewpoint of three substituent effects; interior 10 b, 10 c-positions of the dihydropyrene molecules, 4, 5, 9 and 10-positions of the conjugated rings, and the t-butyl groups at 2,7-positions. The substituent effects were elucidated as follows: (1) the rate constants of the thermal coloration reactions were increased and the quantum yields of the photo-decoloration reactions were decreased when the bulky groups were substituted at 10b, 10c-positions, (2) the rate constants did not changed, but the quantum yields were increased, when an electron withdrawing group such as an acetyl group or a nitro group was introduced at 4-position, (3) the t-butyl groups at 2, 7-positions considerably decreased the quantum yields and caused the degradation reaction. © 1988, The Chemical Society of Japan. All rights reserved.