Photochromism of 2H-Naphtho[1,2-b]pyrans: A Spectroscopic Investigation

Abstract

The photophysical and photochromic properties of 2,2-diphenyl-2H-naphtho[1,2-b]pyran and substituted derivatives were investigated by steady state and time-resolved optical absorption and emission spectroscopy in solution at room temperature and in a frozen matrix at 77 K. Fluorescence quantum yields, fluorescence lifetimes, and singlet energies depend strongly on the substitution patterns. Photoexcitation of the naphthopyrans (A) leads to efficient ring opening to produce the merocyanines (B) and (C). The optical absorption of the merocyanines can be tuned by the substituents and can cover most of the visible spectrum (400−700 nm). The decoloration kinetics of the open forms (merocyanines) B and C to produce naphthopyrans (A) depends strongly on the substituents. The ring closure rate constants (kB→A) range from 0.0009 to 0.04 s-1.