Meta-conjugation and excited-state coupling in phenylacetylene dendrimers

Traditional pictures of optical properties in phenylacetylene dendrimers view the molecule as a collection of independent chromophores, linked by meta-substitution at the central phenyl ring. While this picture is reasonable for explaining the observed absorption trends, it breaks down in describing the emission behavior. We utilize a combination of ab initio theory and experiment to demonstrate that differences in the absorbing and emitting states can be described using an exciton model with very weak chromophore coupling for the absorption geometry and strong coupling for the emission geometry. This result may have significant implications for the design of energy-funneling dendrimeric molecules.