Conformation-dependent excited-state dynamics and transient absorption in dibenzoterrylene.

Dibenzoterrylene (DBT) is an organic single-photon emitter widely studied for applications in quantum optics and molecular photonics. Although DBT is not typically regarded as a highly flexible molecule, its energy landscape exhibits multiple low-energy conformations with distinct vibrational and electronic properties. Here, we show that the excited-state dynamics of these conformers are markedly different and can be distinguished through transient absorption spectroscopy. Using nonadiabatic excited-state molecular dynamics simulations, we compare the ultrafast photophysics of two representative DBT conformers. Although both structures display similar low-energy optical transitions, their excited-state dynamics diverge significantly following photoexcitation, resulting in distinct relaxation timescales and transient spectral signatures. The observed differences in relaxation dynamics occur despite the involvement of a common vibrational coordinate in the dominant nonadiabatic relaxation pathway, indicating that the efficiency of energy flow along this coordinate is conformer dependent. Our results establish transient absorption spectroscopy as a sensitive probe of DBT conformational heterogeneity and demonstrate that conformer-dependent photodynamics can generate experimentally distinguishable ultrafast spectroscopic signatures.