Theoretical characterization of a multifunctional electrooptical molecular device: Photochemical ring-opening mechanism of indolinospirobenzopyran

摘要

Geometries of the spiro form (SP) and the merocyanine form (MC) of 1,3,3-trimethylspiro(2H-1-benzopyran-2,2'-indole) and the 6'-nitro-substituted analog were calculated at the AM1, HF/3-21G, and B3LYP/3-21G levels of theory. The geometry of the lowest excited state of both forms was calculated utilizing the CIS/3-21G method. The ring-opening mechanism and the spectroscopy of both systems were investigated. The earlier proposed mechanisms, based on time-resolved transient absorption spectroscopy, were confirmed in most details. The low-lying n --> pi* state of the 6'-nitro-substituted spiropyran, absent in the unsubstituted spiropyran, causes the rather different photochemical behavior of the two systems. The proximity of the first n --> pi* state and the low-energy pi --> pi* state opens up an exit channel to the triplet manifold, which complicates the mechanism. Solvent effects play an important role for the formation of the final merocyanine product fur the 6'-nitro-substituted spiropyran. A new interpretation of the observed transient absorption spectrum of SP-H and new assignments of some of the peaks if the MC-NO, spectrum are proposed. (C) 2000 John Wiley & Sons, inc. [References: 23]