First-Principles Prediction of Wavelength-Dependent Product Quantum Yields.

We present a method to predict wavelength-dependent product quantum yields (PQYs) for photochemical reactions and applied it to Z/E-isomerization and several ring-closing reactions of Z-2,5-dimethyl-1,3,5-hexatriene and truncated previtamin D. Using branching ratios from surface hopping molecular dynamics, individual trajectories are correlated with the absorption spectra of their initial structures. The wavelength-dependent PQYs are computed by dividing the average spectrum of the initial structures of the product-forming trajectories by the average spectrum of all initial structures. Accurate absorption spectra are calculated using the correlated ADC(2) method with an implicit solvent. Calculations reproduce the experimentally found trend of increasing six-ring formation and decreasing Z/E-isomerization on the red side of the spectrum. Over all seven reactions studied, the mean absolute error (MAE) between experimental and calculated PQYs (MAE) amounts to 8.1%, and the largest MAE is 18.6%. For four reactions, predicted values agree quantitatively with experiments within 5.6%.