Two-state resonance narrowing model and verification of organic molecule emission spectra

Electron-vibrational coupling theory quantitatively describes organic molecular spectra and is key to understanding spectral broadening. However, organic molecular vibrational modes are discrete, high-frequency, and multimode-coupled; a unified framework that condenses mode-resolved information into a single, physically meaningful descriptor remains lacking. To this end, we employ the two-state resonance (TSR) model to construct a unified framework in which the resonance coefficient c2 is a core descriptor for the charge-reorganization response of a molecule along the neutral-zwitterionic coordinate; in the presence of an external polarizing field such as a solvent field, it also reflects sensitivity to solvation perturbations. For typical heteroatom narrowband emitters, fitting FWHM against TSR parameters enables estimation of the limit and guides the design of high-color-purity emitters.