The excited-state dynamics of the radical anions of cyanoanthracenes

Abstract

The radical anion of 9,10-dicyanoanthracene (DCA) has been suggested to be a promising chromophore for photoredox chemistry, due to its nanosecond excited-state lifetime determined from indirect measurements. Here, we investigate the excited-state dynamics of the radical anion of three cyanoanthracenes, including DCA˙⁻, produced by photoinduced electron transfer in liquid using both pump–probe and pump–pump probe transient electronic absorption spectroscopy. All three excited radical ions are characterised by a 3–5 ps lifetime, due to efficient non-radiative deactivation to the ground state. The decay pathway most probably involves D₁/D₀ conical intersection(s), whose presence is favoured by the enhanced flexibility of the radical anions relative to their neutral counterparts. The origin of the discrepancy with the nanosecond lifetime of DCA˙⁻* reported previously is discussed. These very short lifetimes limit, but do not preclude, photochemical applications of the cyanoanthracene anions.