Manifestation of Molecular Chromophore Polymorphism in Diffuse Vibronic Spectra

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 ν_i0. 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.