Triplet 1-nitronaphthalene and competitive energy and electron transfer reactions with trans-stilbene

A time resolved resonance Raman (TR³) study of 1-nitronaphthalene (1NN) first triplet excited state in various solvents is combined with ab initio calculations to determine the nature and the geometry of this state in environments of different polarity. A transient absorption and TR³ study of the reactions of triplet 1NN with trans-stilbene (tS) in solution in both non-polar and polar solvents is reported. In polar solution, ³1NN acts as an electron acceptor whereas in non-polar solution only energy transfer to tS is observed. Moreover, at high concentrations of tS, the radical cation tS⁺ reacts with ground-state tS to form a dimer radical cation (tS₂)^+.. Differences between the Raman spectra of the monomeric and the dimeric radical cations are reported in the 1500-1650 cm^-1 region. The switch from energy to electron transfer when going from non-polar to polar solutions is discussed in terms of the Marcus-Hush theory of electron transfer.