The energy and isotope dependence of electronic relaxation in dilute vapors of fluorene and β-naphthylamine

The excitation energy and isotope dependence of fluorescence lifetimes and quantum yields in dilute vapors of fluorene and β-naphthylamine are discussed in relation to the manner in which different channels of radiationless transitions are affected by the vibrational energy content of the molecule. Evidence is presented which shows that vibrational relaxation is slow compared with electronic relaxation for molecules with low excess energies and that the rate of S₁ → S₀ internal conversion is greater in the deuterated compound than in the corresponding protonated species for very large excess energies.