Synthesis and photochromic behaviour of novel 2H-1-benzopyrans (=2H-chromenes) derived from carbazololes

The synthesis and photochromic properties of new 2,2-diphenyl-2H-1-benzopyrans, fused to an indole moiety, are described. All compounds exhibit photochromic behaviour in solution at room temperature. The heteroanellation effects are variable and depend on the position and geometry of the fused indole moiety. A general bathochromic shift in the spectra of the open forms is observed. The presence of a N-methyl group prevents the broadening of the absorption spectra and promotes the instability of some photoinduced forms of compounds with the indole moiety fused at the 5,6 positions of the 2H-1-benzopyran skeleton. The enhanced photocolouration efficiency in the near-UV and the kinetics of thermal bleaching indicate that the novel compounds with an indole moiety fused at the 6,7 positions, particularly those with a linked thiophene moiety: are very interesting molecules for applications in the field of variable optical absorption systems.