Spatial extent of the singlet and triplet excitons in transition metal-containing poly-ynes

D Beljonne, HF Wittmann, A Köhler, S Graham, M Younus, J Lewis, PR Raithby, MS Khan, RH Friend, JL Brédas

J. Chem. Phys. 105 (1996) 3868-3877.

We present a joint experimental and theoretical investigation of the electronic excitations in transition metal-containing phenylene ethynylenes. The influence of the metal on the nature of the lowest singlet and triplet excited states is characterized. We find that p conjugation occurs through the metal sites, which deeply modifies the optical properties of the conjugated chains. We also analyze the chain-length dependence of the singlet–singlet, S0?S1, singlet–triplet, S0?T1, and triplet–triplet, T1?Tn, transition energies; both experimental data and theoretical results indicate that the lowest triplet exciton, T1, is strongly localized on a single phenylene ring while the S1 and Tn states extend over a few repeating units. Finally, we estimate the geometric relaxation phenomena occurring in the lowest excited states and perform a Huang–Rhys analysis of the triplet emission spectrum in model systems.