Abstract
The influence of proaromaticity on the excited state dynamics of near-infrared (NIR)-absorbing sensitizer dyes is explored using a combination of ultrafast transient absorption spectroscopy (TAS) and computational chemistry. The addition of a proaromatic π-bridge was found to stabilize the excited state and lead to lower excitation energies in solution and longer excited-state lifetimes, contrary to what is expected by the energy gap law. When studied under standard device conditions on TiO2, it was found that the dye structure plays a significant role in determining excited-state dynamics. Computational chemistry results confirm the proaromatic nature of the dyes through both bond length analyses and nucleus-independent chemical shift (NICS) calculations. Through incorporation of excited-state aromaticity, a 10× increase in excited-state lifetime was observed for dyes with a near 0.5 V lower energy excited state.
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