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The excited states of fac-tris(phenylpyridinato)iridium[Ir(ppy)3] and the smaller model complex Ir(C3H4N)3are computed using a number of high-levelab initio methods, including the recently implemented algebraic diagrammaticconstruction method to third-order ADC(3). A detailed descriptionof the states is provided through advanced analysis methods, whichallow a quantification of different charge transfer and orbital relaxationeffects and give extended insight into the many-body wave functions.Compared to the ADC(3) benchmark an unexpected striking differenceof ADC(2) is found for Ir(C3H4N)3, which derives from an overstabilization of charge transfer effects.Time-dependent density functional theory (TDDFT) using the B3LYP functionalshows an analogous but less severe error for charge transfer states,whereas the ωB97 results are in good agreement with ADC(3).Multireference configuration interaction computations, which are inreasonable agreement with ADC(3), reveal that static correlation doesnot play a significant role. In the case of the larger Ir(ppy)3complex, results at the TDDFT/B3LYP and TDDFT/ωB97levels of theory are presented. Strong discrepancies between the twofunctionals, which are found with respect to the energies, characters,as well as the density of the low lying states, are discussed in detailand compared to experiment. [ABSTRACT FROM AUTHOR]

The photodecarboxylation mechanismof different structural isomersof nitrophenylacetate (NPA) has been investigated using quantum chemicalcalculations as well as time-resolved UV-pump VIS-probe spectroscopy.It is shown that for a proper theoretical description of the excitedstates of anionic NPA in aqueous solution a careful considerationof the influence of the solvent is indispensable. In this sense, NPAis an example that demonstrates how character and lifetime of theinvolved excited states affect the results of equilibrium and nonequilibriumsolvation approaches. An ultrafast decay channel via a repulsive singletstate has been found to be responsible for observed ultrafast CO2release, while another very efficient but slower CO2release channel is found to proceed via intersystem crossing andsubsequent decay via a repulsive triplet state. After all, differencesand similarities in the observed excited state dynamics of the isomersare conclusively explained. Most notably, the much smaller quantumyield of CO2release from the ortho-isomer is due to analternative excited-state hydrogen-transfer channel, which occursalong a triplet and singlet pathway. On the basis of theoretical andexperimental evidence suggesting that the multiplicity of the routetaken determines the photoproduct yield, we provide guidelines forthe design of ortho-nitrobenzylic caging groups with improved uncagingyield. [ABSTRACT FROM AUTHOR]