Excitonic Coupling and Photon Antibunching in Venus Yellow Fluorescent Protein Dimers: A Lindblad Master Equation Approach

Abstract

Strong excitonic coupling and photon antibunching (AB) have been observed together in Venus yellow fluorescent protein dimers and currently lack a cohesive theoretical explanation. In 2019, Kim et al. demonstrated Davydov splitting in circular dichroism spectra, revealing strong J-like coupling, while antibunched fluorescence emission was confirmed by combined antibunching--fluorescence correlation spectroscopy (AB/FCS fingerprinting). To investigate the implications of this coexistence, Venus yellow fluorescent protein (YFP) dimer population dynamics are modeled within a Lindblad master equation framework, testing its ability to cope with typical, data-informed, Venus YFP dimer time and energy values. Simulations predict multiple-femtosecond (fs) decoherence, yielding bright/dark state mixtures consistent with antibunched fluorescence emission at room temperature. Thus, excitonic coupling and photon AB in Venus YFP dimers are reconciled without invoking long-lived quantum coherence. However, clear violations of several Lindblad approximation validity conditions appear imminent, calling for careful modifications to choices of standard system and bath definitions and parameter values.