SPECTROSCOPY AND PHOTOCHEMISTRY OF FLUORENE AT A SILICA GEL AIR INTERFACE/

The emission spectroscopy of fluorene has been studied at a silica gel /air interface at surface loadings from 1.5% to 77.1% of a monolayer. Both monomer and excimer-like emissions are observed on the surface. T he excimer-like emission, centered at 350 nm, arises from excitation o f ground-state van der Waals pairs of fluorene molecules. Photolysis i nto the van der Waals dimers at room temperature does not lead to diss ociation into constituent monomers; however, irradiation of fluorene m onomers at a silica gel/air interface leads to production of 9-fluoren one as the only identifiable photoproduct in 72% yield. Fluorene tripl et and cation radical are both observed at the silica gel/air interfac e by transient diffuse reflectance spectroscopy. Sensitization of sing let molecular oxygen by silica-sorbed methylene blue, in the presence of co-sorbed fluorene, does not lead to fluorene oxidation, thus sugge sting that oxidation by direct photolysis does not involve an energy t ransfer mechanism. An electron transfer oxidation mechanism is propose d to account for the observed photochemical oxidation of fluorene at t he silica gel/air interface. (C) 1997 Published by Elsevier Science S. A.