Manifestation of Molecular Chromophore Polymorphism in Diffuse Vibronic Spectra

Abstract

The location of the purely electronic 0–0-transition v0 for homomorphic chromophores is defined in the transition cross-section spectrum σ(ν) by the extremum (∂φ/∂v = 0) of the function [σ(ν)/ν] exp ((∓hv/2kT) = φ(|v − v0|) and "–" for absorption, ν < ν0 and "+" for emission) for the dipole Frank–Condon transition with thermal distribution among the initial-state sublevels. The observed effective cross section and spectrum with polymorphism are formed by partial contributions of electronic transitions of the separate species with different νi0. In this instance, the homomorphic extremum is distorted, i.e., broadened, weakened, or absent, which is also indicative of a polymorphic chromophore. Examples of these distortions of the functions calculated from the experimental spectra are given.