Theoretical and Experimental Assessment of the Absorption and Dual Emission of Benzobisthiadiazole Conjugated Oligoelectrolyte Probes

The conjugated oligoelectrolyte <b>COE-BBT</b> and its neutral form, <b>BBT-Br</b>, are probes based on benzobisthiadiazole and thiophene-stilbene units with near-infrared emissions. Upon photoexcitation, these compounds exhibit a second emission band, suggesting anti-Kasha character of their fluorescence. Here, we disclose theoretical evidence in support of the non-Kasha behavior of BBT probes. We employ time-dependent density functional theory (TD-DFT) and nonadiabatic molecular dynamics to simulate and analyze absorption and emission phenomena, providing a comprehensive understanding of the electronic and structural excited-state behavior and photophysical properties. In particular, our results support the presence of two distinct excited states from where emission is possible.