Enhancement of Energy Transfer Efficiency with Structural Control of Multichromophore Light-Harvesting Assembly

Multichromophore systems (MCSs) are envisioned as building blocks of molecular optoelectronic devices. While it is important to understand the characteristics of energy transfer in MCSs, the effect of multiple donors on energy transfer has not been understood completely, mainly due to the lack of a platform to investigate such an effect systematically. Here, a systematic study on how the number of donors (n_D) and interchromophore distances affect the efficiency of energy transfer (η_FRET) is presented. Specifically, η_FRET is calculated for a series of model MCSs using simulations, a series of multiporphyrin dendrimers with systematic variation of n_D and interdonor distances is synthesized, and η_FRETs of those dendrimers using transient absorption spectroscopy are measured. The simulations predict η_FRET in the multiporphyrin dendrimers well. In particular, it is found that η_FRET is enhanced by donor-to-donor energy transfer only when structural heterogeneity exists in an MCS, and the relationships between the η_FRET enhancement and the structural parameters of the MCS are revealed.