The polarizability of triplet excitons on oligothiophene chains

The excess polarizability volume, ΔVp, associated with the formation of the T1 states of oligothiophenes, OTn with n from 2 to 12, has been determined by measuring the change in the imaginary component of the complex microwave conductivity resulting on flash-photolysis of dilute solution. ΔVp gives a direct measure of the additional electronic delocalization associated with the halffilled HOMO and LUMO orbitals of these states. ΔVp increases with increasing length of the oligomer chain from 5 Å3 for n=2 to 59 Å3 for the dodecamer. The increased delocalization in T1 is discussed in terms of coupling with higher states in the triplet manifold.