Light harvesting in dendrimer materials: Designer photophysics and electrodynamics

Multichromophoric dendrimers are increasingly being considered for solar energy systems. To design materials with suitably efficient photon collection demands a thorough understanding of crucial photophysical conditions and electrodynamic mechanisms, many of which prove to emulate photosynthetic systems. Key parameters include the chromophore absorption properties, the generation, branching and folding of the dendrimer, and the presence of a spectroscopic gradient. Driving excitation towards a trap, resonance energy transfer favors migration between nearest neighbor chromophores. In modeling the progress of excitation from antenna chromophores towards the trap, a propensity matrix method has broad applicability, giving physical insights of generic validity. Calculations on specific dendrimers are best served by quantum chemistry models; again, links with photobiological systems can be discerned. Two important optically nonlinear features are cooperative energy pooling, and two-photon energy transfer. Branch multiplicity and the polar or polarizable nature of the chromophores also play important roles in determining energy harvesting characteristics.