Photochromism of 10 b, 10 c-Dihydropyrene Derivatives with the t-Butyl 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 10 b, 10 c-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.