Preparation of lamellar inorganic-organic hybrids from tetraethoxysilane and a coumarin derivative containing a triethoxysilyl group and photodimerization of the interlayer coumarin groups

Lamellar inorganic-organic hybrids were prepared as powders and films via hydrolysis and cocondensation of tetraethoxysilane (TEOS) and a coumarin derivative containing a triethoxysilyl group. The formation of lamellar structures consisting of siloxane layers and interlayer coumarin groups with ca. 4 nm periodicities, revealed by XRD and TEM, is induced by self-assembly of the oligomeric species derived from TEOS and the derivative. The UV-vis absorption spectrum of the as-synthesized hybrid film showed an absorption maximum blue-shifted from that observed for a CHCl₃ solution of the monomeric coumarin derivative, which supports the formation of a face-to-face structure of the interlayer coumarin groups. Dimerization of the coumarin groups occurred by irradiation with visible light (>310 nm). The groups in the lamellar hybrid film showed faster dimerization and the yield of dimers was higher, if compared with those in a disordered hybrid film and the neat coumarin derivative, indicating the efficient dimerization of the chromophores with a controlled arrangement. The molecular design of a coumarin derivative strongly influences the property of hybrids as well as the mesostructural formation.