Estimation of the solvent reorganization energy and the absolute energy of solvation of charge-transfer states from their emission spectra

CLAUDIA SOLIS; VIVIANA GROSSO; NATHANIEL FAGGIOLI; GONZALO COSA; MARIO ROMERO; CARLOS PREVITALI; HERNÁN MONTEJANO; CARLOS CHESTA

Photochemical and Photobiological Sciences

RSC Publishing

Año: 2010 vol. 9 p. 675 - 686

1474-905X

We report herein the solvent and temperature effects on the emission of the intermolecular exciplexes 1-cyanonaphthalene/triethylamine and 1-methylnaphthalene/triethylamine and the intramolecular exciplexes formed by the bichromophoric compounds diethyl-(3-naphthalen-1-yl-propyl)-amine (I), diethyl-(2-naphthalen-1-yl-ethyl)-amine (II), 3-[ethyl-(2-naphthalen-1-yl-ethyl)-amino]-propionitrile (III) and 3-[(2-cyano-ethyl)-(2-naphthalen-1-yl-ethyl)-amino]-propionitrile (IV). The results are interpreted within the formalism of the semiclassical Marcus theory for radiative back electron transfer (BET) reactions. We show that, following a few simple assumptions, reliable values of the Gibbs free energy changes and the solvent reorganization energies associated to the BET reactions (and their corresponding enthalpic and entropic contributions) can be estimated directly from the emission of the CT states. We also show that for the 1-cyanonaphthalene/triethylamine exciplex, whichexhibits emission in the vapour phase, the experimental calculation of the absolute energy of solvation of the CT state is also possible. The calculated DGe-et correlate quite satisfactorily with the corresponding values obtained from independent electrochemical and kinetics experiments. The temperature effects on DGe-et, les and DGes are discussed qualitatively using different solvation models. The limitations of the present approach for the estimation of DGe-et and les and its possible application to more complex A/D systems are also examined.