Photochromism and solvatochromism of push–pull or pull–push spiroindolinenaphthoxazines

Abstract

The photochromic and solvatochromic behaviour of 17 variously substituted spiroindoline naphthoxazines has been investigated in cyclohexane, toluene, acetonitrile and methanol in fluid solution. Specific parameters such as the wavelengths and the molar absorption coefficients of the closed spiro- and open merocyanine forms, together with the photocoloration and photobleaching quantum yields, rate constants and activation energies of thermal fading have been determined under continuous monochromatic irradiation. It has been shown that most of these parameters are closely related to the electron distribution on the highly conjugated photomerocyanines and on their quinoidal or zwitterionic character. Depending on the acceptor or donor properties and on the position of their substituents, three classes of compounds have been detected.