Exploring the Concept of Dimerization-Induced Inter System Crossing: at the Origins of Spin-Orbit Coupling Selection Rules

Abstract : Singlet-Triplet interconversions and transitions (intersystem crossing, ISC) in organic molecules are at the basis of many important processes in cutting-edge photonic applications (Organic Light Emitting Devices, photodynamic therapy…). Selection rules for these transitions are mainly governed by the Spin-Orbit Coupling (SOC) phenomenon. Although the latter relies on complex relativistic phenomena, theoreticians have, with time, developed increasingly sophisticated and efficient approaches to gain access to a satisfactory evaluation of its magnitude. In this work, we bring a coupled experimental and theoretical analysis of the origin of the unusually large ISC efficiency on a series of dimers that differ by their nature (covalent or supramolecular) as well as the distance and relative orientation of their individual chromophoric components. The dynamical nature of the SOC, sometimes overlooked in literature, is discussed in deep.