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.