Probing structure-property relationships of BODIPY dimers on the efficiency for symmetry breaking charge transfer*

Symmetry breaking charge transfer (SBCT) is the process in which a pair of identical chromophores are coupled such that post excitation an exciton (electron-hole pair) can dissociate between the two chromophores. The product is an uncoupled, spatially separated electron and hole pair, reducing the probability of recombination. The resulting uncoupled charges from SBCT are beneficial for photoelectrochemical and photovoltaic applications. BODIPY dimers have been shown to undergo SBCT in femto-to-pico-second timescales¹. The dipyrrinato dimer analogues have also been studied and shown to undergo SBCT where they are ligated via the nitrogen termini through a zinc (II) center². Herein the BODIPY and dipyrrinato dimers are analyzed to understand the effect of different bridging methods and increased substituents on the efficiency of SBCT. Efficiency in the context of this analysis is the rate of formation and longevity of the SBCT state. We find that direct linkage where torsion is not sterically hindered results in the fastest SBCT formation and that orthogonally fixed geometries result in the slowest decay times of the SBCT state.

1. Whited M. T. et al. Chem. Commun., 2012, 48, 284 – 2846.
2. Trinh C. et. al. J. Phys. Chem. C. 2014, 118, 21834 – 21845.