Quantum dynamics of photoexcited charge transfer in bridge-mediated porphyrin–naphthalenetetracarboxylic dianhydride donor–acceptor system

Abstract

Photoinduced charge transfer (CT) in donor–bridge–acceptor (D-B-A) systems is governed by the interplay between electronic coupling and vibronic interactions. Here, we investigated ultrafast CT dynamics in Zn-porphyrin–NTCDA complexes connected through either an extended 1,4-diethynylphenylene (DEP) bridge or an ethynyl linker. The excited-state dynamics are described using a linear vibronic coupling Hamiltonian combined with quantum dynamical wavepacket propagation, thereby allowing explicit treatment of multidimensional nuclear motions. Electronic-structure analysis shows that the conjugated DEP bridge provides stronger donor–acceptor communication and more favorable energetic alignment between locally excited and CT states. As a result, population transfer to the CT configuration occurs on an ultrafast timescale of ∼9 fs. In contrast, modifying the bridge reduces π-conjugation and electronic interaction, leading to slower CT dynamics of ∼25 fs. Systematic inclusion of increasing numbers of vibrational modes reveals that cooperative multimode coupling enhances vibronic dephasing, stabilizes the charge-separated population, and suppresses coherent recurrences in the electronic dynamics. The simulations, therefore, identify bridge-mediated conjugation and multidimensional vibronic interactions as key factors governing charge-separation efficiency in these architectures. These findings provide molecular-level insights into how bridge structure and vibrational motions cooperatively regulate CT dynamics in D-B-A systems.