Photokinetic behaviour of bi-photochromic supramolecular systems - Part 3. Compounds with chromene and spirooxazine units linked through ethane, ester and acetylene bridges

The photochemistry of four bi-photochromic (BiPh) compounds was investigated in toluene solution under steady state irradiation over a 20degreesC temperature range. Three of these supermolecules are built up by two chromene moieties linked by a rigid acetylenic bridge (1) or flexible spacers, ethane (3) and ester (4); the other contains a chromene and a spirooxazine moieties linked by an ester bridge (2). Very efficient photo-colouration occurred upon UV irradiation at room temperature. Two of these systems (1 and 2) behaved as classical thermoreversible photochromic systems, while the other two compounds investigated (3 and 4) exhibited thermal and photochemical reversibility. This behaviour was attributed to formation of two (for 3) and three (for 4) photoproducts with different thermal and photochemical stability. By analytical and graphical treatments of the kinetic equations describing the dynamic behaviour of these photochromes, spectral, photochemical (quantum yields) and kinetic (rate constants and activation energies) parameters of these photochromic systems were determined. (C) 2002 Elsevier Science B.V. All rights reserved.