Effects of the substituents on 4′-position on the photon-mode erasable photochromic system of 2-hydroxychalcone derivatives

To establish a photon-mode erasable optical memory system with non-destructive readout ability, photochemistry of the intermediate(s) of photochromic reaction between trans-2-hydroxychalcones and flavylium cations has been studied. The photochromic intermediates in acetonitrile have been assigned to be flav-3-en-2-ol for 4′-cyano as in the case of non-substituted one and equilibrated mixture of flav-3-en-2-ol and cis-form for 4′-methoxy derivative, and cis-form for 4′-dimethylamino derivative. The absorption spectra of flavenol derivatives have been almost independent of the substituent at 4′-position. Although photochemical formation quantum yield of flav-3-en-2-ol into trans-2-hydroxychalcone were independent of the substituent at 4′-position, 4′-OMe derivative has shown the highest conversion yield in the photostationary state. The reaction mechanism of photochromic intermediate(s) to give trans-2-hydroxychalcone has been also clarified by nanosecond transient absorption technique. By making use of this photochemical reaction, we demonstrated the indirect photon-mode erasing of photochemically stable flavylium cation in both solution and polymer film of 4′-methoxy derivative. Reversibility has been also studied.