Photoinduced Charge-Transfer Reactions of Tricyanoethlene with Aromatic Hydrocarbon Electron Donors. I. Emission Studies of Naphthalene-Tricyanoethylene Exciplex |
| J. Dresner, K. Kwapisz, I. Deperasińska, J. Prochorow Institute of Physics, Polish Academy of Sciences, al. Lotników 32/46, 02-668 Warsaw, Poland P. Bruni, A. Giardina and G. Tosi Dipartimento di Scienze dei Materiali e della Terra Universita degli Studi di Ancona, via Brecce Bianche, 60131 Ancona, Italy |
| Received: March 11, 2002; in final form June 29, 2002 |
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| The fluorescence quenching of a series of aromatic hydrocarbon electron donors by an electron acceptor tricyanoethylene has been observed. The quenching mechanism is consistent with the charge-transfer (or electron-transfer) mechanism, as indicated by the appearance of a new, broad, and structureless exciplex emission band. Detailed, steady-state, and time-resolved emission studies of the kinetics and thermodynamics of exciplex formation and relaxation have been performed for naphthalene-tricyanoethylene system. It was found that the kinetics of monomer-exciplex equilibrium for this system, in a non-polar solvent (n-hexane), can be described in terms of a simple two-state photokinetic scheme. Within such a scheme, under conditions of the present experiment, napthalene-tricyanoethylene system approaches the limits under which exciplex formation is very effective --- it becomes exclusively diffusion-controlled and at the same time a competitive process of thermal dissociation of exciplex ceases to operate. This leads to a very rarely observed reversal of physical meaning of the decay parameters which are describing the rise and the decay of exciplex fluorescence. |
| DOI: 10.12693/APhysPolA.102.443 PACS numbers: 82.30.Fi, 82.60.Hz, 32.50.--j |