Abstract
The ultrafast excited state decay rates for indenofluorene and fluorenofluorene derivatives as measured by transient absorption spectroscopy are reported. The excited state lifetimes of the molecules were extremely short (ca. 9-12 ps) and are a result of the p-xylylene motif in indenofluorenes and the corresponding expanded 2,6-naphthoquinonedimethide in fluorenofluorene. Quantum chemical calculations indicate that the fast relaxation to the ground state results from a potential energy surface crossing between the So and 51 states. This process in turn provides an efficient route for excited state deactivation and explains why this class of quinoidal molecules is non-emissive. (C) 2014 Elsevier B.V. All rights reserved.