Exciton-driven photoisomerization in photoswitch-quantum dot nanohybrids

Nanohybrid systems in which semiconductor quantum dots (QDs) functionalize molecular photoswitches (PhSs) offer a promising platform for light-responsive materials. These systems leverage the reversible photoisomerization of PhSs and the size-tunable optical properties of QDs to enable functionalities in biomedicine, catalysis, and sensing. While strong light-matter coupling has been used to modulate photoisomerization in PhSs, such approaches are limited by ultrafast dynamics and the requirement for resonant cavity architectures. Here, we propose intrinsic excitonic coupling to shape photoisomerization pathways, taking advantage of the nanosecond-scale lifetimes of such hybrid states and the lower structural complexity of QD-based systems. Specifically, by applying the recently developed hybrid configuration interaction - a non-perturbative multiscale approach - to azobenzene and cadmium selenide quantum dots, we show avoided crossings near resonance between the photoswitch M₀ → M₁ transition and the lowest QD exciton, accompanied by excitonic splittings in the few meV range. Analysis of hybrid dipoles shows a redistribution of oscillator strength between the molecular and QD components, confirming the delocalized nature of the excitations. These results demonstrate that cavity-free PhS-QD nanohybrids can exhibit coherent excitonic reshaping of molecular photoisomerization, highlighting their potential as tunable, light-driven nanodevices.