Design of π-Conjugated Donor-Bridge-Acceptor Radicals for Molecular Qudit Applications

Organic radicals with spin-polarized excited-state manifolds are attractive molecular platforms for quantum information technologies. A central challenge lies in the understanding of how emissive doublet states can communicate with higher-spin quartet states while maintaining efficient luminescence. In this context, we propose here a series of donor-bridge-acceptor radicals based on anthracene or naphthalene donors coupled to the tris(trichlorophenyl)methyl (TTM•) radical acceptor. By combining excited-state electronic-structure analysis with interpolated coordinate pathways, we reveal how the locally excited (LE) states and charge-transfer (CT) states govern the accessibility of quartet manifolds and enable radical-enhanced reverse intersystem crossing (ERISC). Structural variations, including steric hindrance and donor–acceptor spatial separation, are shown to modulate the CT-state characteristics and reshape the LE-CT energy landscape. Our results identify the electronic-structure requirements and molecular design strategies for achieving both optically addressable emission and manipulation of quartet states, two key ingredients for molecular qudit architectures.