Multiple emissions of α-naphthil: fluorescence from S2 state

Multiple emissions of α-naphthil are reported in solution phase at room temperature as well as in ethanol glassy matrix at 77 K, frozen under different conditions of illumination. Steady state and time-resolved fluorometric measurements are undertaken to assign the observed emissions to the different species in terms of geometry and electronic states of the fluorophore. The unexplored emission band peaking at ∼423 nm has been ascribed to originate from the S2 electronic state. Exhaustive experiments reveal that while the trans conformer of α-naphthil gives only the S1 emission, the conformation with a geometry close to the ground state one emits from both S1 and S2 electronic states depending on the excitation wavelength.