Lowest singlet excited state and spectroscopy of α-carotene

Emission, excitation and absorption spectra of α-carotene have been measured in solvents with different polarizabilities. It is shown that in highly-polarized solvents α-carotene emits weak fluorescence from the S1(π,π∗) state with the fluorescence origin observed at 14 800 ± 200 cm−1. The relative S1/S2 fluorescence intensity ratio tends to increase with increasing solvent polarizability or decreasing the S1–S2 energy separation. The obtained spectroscopic data include the Raman spectrum of α-carotene along with the vibrational analyses of the Raman spectrum based on the DFT calculation at the B3LYP/6-31G(d,p) level.