Following excited states in molecular systems using density-based indexes: A dual emissive system as a test case

Abstract

Dual emission from single molecular species is a particularly appealing phenomenon to test the efficiency of theoretical approaches for the description of a complex excited state scenario.Recently, the Phen-PENMe2 molecule (Phen-PENMe2 = 5-(4-dimethylaminophenylenylethylyn)-1,10-phenanthroline) has been experimentally characterized and its dual emission has been ascribed to the presence of two emissive states of different electronic nature and corresponding to two structurally different species. Nonetheless, the full mechanism ruling the structural interconversion leading to dual emission has not yet been disclosed.To this end, in this paper the dual emissive behavior of Phen-PENMe2 has been unveiled by a combined use of time dependent density functional theory (TD-DFT) and density-based indexes (DCT and Π) allowing identifying the radiative and non-radiative decay pathways at work in this system. In particular, the possible presence of an anti-Kasha emission mechanism as well as the presence of several non-radiative decay channels allowing enhancing either of the two emissions has been proven.More generally, the results obtained in the present study highlight how this simple and inexpensive computational approach may be of help and general interest for the rational design of new dual emissive systems.