J. Photochem. Photobiol. A: Chem., 57 (1991) 41-63 41 zyxwvu Room temperature phosphorescence and delayed fluorescence of organic molecules trapped in silica sol-gel glasses David Lev~“-~ and David Avnirb “Institute de Ciencia de Materiaies de Madrid, CSIC, Serrano, 115 dpdo, Madrid 28006 (Spain) bDeparrment of Organic Chemistry and the F. Haber Research Centre for Molecular Dynamics, The Hebrew Universiry of Jerusalem, Jerusalem 91904 (Israel) zyxwvutsrqponmlkjihgfedcbaZYXWVUT (Received November 6, 1990) Abstract Room temperature phosphorescence (RTP) is obtained from a wide variety of organic molecules when trapped in silica matrices prepared by the “sol-gel” polymerization process of tetramethoxysilane. Examples include polycyclic hydrocarbons, aromatic acids, an aromatic base (quinine) and an organic dye (eosin-y). Lifetimes of up to several seconds are observed. Conditions for observing RTP vary. In some cases co-trapping of a heavy atom is needed, whereas in others RTP is observed even in wet gels without a heavy atom. A detailed study of the phenomenon was performed with 4-biphenylcarboxylic acid. It RTP and delayed fluorescence properties were studied as a function of base concentration, reaction time and temperature (Arrhenius analysis), revealing a multitude of emitting species (the acid and its anion, either adsorbed on the silica cage surface or “dissolved” in solvent-rich cages). 1. Introduction One of the major applications of the rapidly developing sol-gel process for low temperature glass preparation [l] is the ability to dope inorganic glasses with organic molecules, especially those which are photoactive [Z-7]. The room temperature polymerization of metal alkoxides has led to the preparation of materials of optical interest such as solid laser dye blocks [2, 4-61 and films [7], photochromic glasses [S, 91, hole-burning materials [3, 10, 111, light guides [12] and non-linear optical materials [13]. Recently, we have extended the application of this type of doped glass to the preparation of photocatalysts and have demonstrated their use in water reduction [14]. Not only have interesting photoactive materials been prepared in these studies, but doping with photoprobes has been intensively used for a detailed mechanistic study of the polymerization process of the metal alkoxide monomers involved [2-171. The method of doping sol-gel glasses with organic molecules has recently been applied for the preparation of chemical sensors [18, 191 and, for the first time, for the preparation of bioactive sol-glasses, by trapping of enzymes [18, 201. We have reported 1211 the observation that the efficient trapping of organic molecules in silica cages enables intense room temperature phosphorescence zyxwvutsrqponm (RTP) to be observed. In this paper, we report a detailed study of the phenomenon, including 10X0-6030/91/$3.50 0 Elsevier Sequoia/Printed in The Netherlands