Spirooxazine- and spiropyran-doped hybrid organic–inorganic matrices with very fast photochromic responses

Both spirooxazine and spiropyran dyes have been embedded into two different hybrid matrices, which were formed from hydrolysis and cocondensation between diethoxydimethylsilane and zirconium propoxide and between methyldiethoxysilane (DH) and triethoxysilane (TH) respectively. The nature and the kinetics of the photochromic response depend strongly on the hydrophobic/hydrophilic balance (HHB) of the hybrid material. The HHB controls the competition between direct and reverse photochromism. The photochromic behaviour of the strongly hydrophobic spirooxazine-doped DH/TH coatings is direct, highly efficient (ΔA>1), reversible and extremely fast (thermal bleaching time constant, k=0.2 s -1 ). The photochromic kinetics of this hybrid material are, to the best of our knowledge, much faster than those reported for spirooxazine in any other solid matrix.