A photophysical and theoretical study of styrylanthracenes

Abstract

The photophysical properties of the three isomeric trans-n-styrylanthracenes (n-StAs, with n= 1, 2, 9), whose lowest excited states are expected to display a prevalent aromatic character, have been studied in different solvents. Fluorescence quantum yields and lifetimes have been measured as a function of temperature in a wide temperature range. All trans compounds, including the two rotamers of 2-StA, are relatively highly fluorescent and do not photoisomerize to the cis compounds. Semiempirical MO + Cl Calculations have been performed to assess the shape of the potential-energy surfaces in the lowest excited states of the compounds investigated. These calculations indicate that S₁ and T₁ in all the n-StAs have a sizeable barrier on the torsional coordinate from trans to cis. The barrier for the cis- to trans- process is expected to be lower. The combined results of the experimental and theoretical studies offer a clear description of the excited-state behaviour of trans StAs.