Description
Nitrobenzochalcogenadiazole derivatives are emerging candidates for Photodynamic Therapy (PDT), yet the precise mechanisms governing their excited-state deactivation and triplet generation remain to be fully elucidated. This study employs non-adiabatic dynamics simulations, using the Trajectory Surface Hopping method within a Linear Vibronic Coupling (LVC) framework, to unravel the Intersystem Crossing (ISC) pathways in these systems. We systematically investigate two design factors: the heavy-atom effect (substituting S with Se and Te) and the influence of “push–pull” electronic architectures (Donor-Acceptor vs. Donor-Donor/Acceptor-Acceptor). Our results demonstrate that replacing Sulfur with Selenium and Tellurium monotonically accelerates ISC, reducing excited-state lifetimes from ≈ 6.1 ps to sub-picosecond timescales (≈ 0.9 ps) via a dominant S2 → S1 → Tn relaxation channel driven by enhanced spin-orbit coupling. Furthermore, we reveal that structural modifications that disrupt this push-pull nature (D-D or A-A) result in kinetic bottlenecks, trapping the population in the singlet manifold. These dynamical insights establish clear structure-property relationships, guiding the rational design of photosensitizers with optimized triplet quantum yields.
