Photophysical and theoretical studies of photoisomerism and rotamerism of trans-styrylphenanthrenes

Abstract

The photophysical and photochemical properties and the ground-state conformational equilibrium of trans-n-styrylphenanthrene (n-StPh, with n = 1, 2, 3, 4, 9) have been studied in inert solvents. The kinetic parameters of the competitive radiative and reactive decay processes have been obtained. A detailed analysis of the fluorimetric behavior as a function of the excitation wavelength and temperature has allowed the distinct decay parameters and the ground-state energy difference of the two rotamers of trans-3-StPh to be obtained. Parallel theoretical calculations of the potential energy curves for the internal rotation of the phenanthryl group in the ground state, of the energies and oscillator strengths of the lowest transitions, and of the activation energies for trans ..-->.. cis isomerization in the ground and lowest excited singlet states have been carried out with a modified (CS) INDO method. The results of the experimental and theoretical studies are in satisfactory agreement and provide a general description of the photophysical and photochemical behavior of this class of compounds.