Using density based indexes to characterize excited states evolution

With the aim of offering new computational tools helping in the description of photochemical reactions and phenomena occurring at the excited state, we present in this work the capability of a density based index (Π) in locating decay channels from higher to lower excited states. The Π index, previously applied to disclose non-radiative decay channels from the first excited state to the ground state, is very simple in its formulation and can be evaluated, practically with no extra computational cost, and coupled to any quantum method able to provide excited states densities. Indeed, this index relies only on the knowledge of energetics and electron densities of the different electronic states involved in the decay. In the present work, we show the proficiency of the Π index in the general case of decay between excited states by applying it to two model systems well characterized both theoretically and experimentally. In both cases, this descriptor was successful in spotting the regions where excited states are more likely to decay, thus suggesting its potential interest for further application in the design of new compounds. © 2018 Wiley Periodicals, Inc.