Excited electronic states and spectroscopy of unsymmetrically substituted polyenes

alpha-Methyl-omega-phenylpolyenes, Me-(CH=CH)(N)-Ph, (MPPNs) with N = 2, 3, and 4 were synthesized. Fluorescence, absorption, and excitation spectra of MPPNs have been measured under different conditions along with those of beta-methylstyrene. It is shown that there is a forbidden singlet (pi, pi*) excited state located at energies below the absorbing state for MPPNs with N = 3 and 4. Excitation energies of these polyenes are determined as a function of N. Quantitative analysis of the temperature dependence of the relative intensity of the fluorescence spectrum and its solvent shift behavior extract estimates of the various physical parameters that characterize excitation energies and excited-state dynamical behavior of MPPN with N = 3. The singlet excited states of the MPPNs were compared with those of the alpha,omega-diphenylpolyenes and alpha,omega-dimethylpolyenes. (C) 2013 AIP Publishing LLC.