Fluorescence excitation spectroscopy of vibronic transitions in single molecules

Fluorescence excitation spectroscopy is used to study vibronic transitions ( S 1 ← S 0 n←0) in terrylene molecules doped in a naphthalene crystal. Evidence for the excitation of individual dye molecules is reported. The average linewidth (FWHM) for transitions to the first and second vibronic levels is, in both cases, 30(4) GHz. Linewidths and vibrational frequencies are not the same for all molecules. A method is presented for establishing a one-to-one correspondence between individual lines in the vibronic and the purely electronic band.