In the condensed phase, almost any molecular photoreaction taking longer than a few picoseconds is governed by thermodynamics. The thermodynamics of excited molecular electronic states has been handled in approximate ways since the work of Forster on excited state proton transfer and of Marcus on excited state electron transfer. An exact determination of the standard chemical potential is available through a generalization of Einstein's treatment of absorption, stimulated emission, and spontaneous emission from line spectra to broadband spectra. However, this treatment is only applicable to homogeneous spectra. 2D electronic spectra can resolve inhomogeneity, allowing these relationships to be applied. Determination of the change in standard chemical potential upon electronic excitation is demonstrated from the 2D electronic spectra of PbS quantum dots. The application of this and related methods to molecular systems will be discussed.

Excited state thermodynamics from 2D spectra

ACS Spring Meeting 2021

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