Simultaneous enhancement of photoluminescence and spin-polarization lifetime in a carbazole-functionalized TTM diradical.

Luminescent organic radicals with multiple spins are emerging molecular platforms for developing optically addressable molecular qubits, and TTM-based diradicals are representative systems that are studied most widely. However, the diradical species thereof typically suffer from low photoluminescence efficiency and short spin-polarization lifetimes, which greatly limit their optical readout sensitivity. Here, we demonstrate that a donor-acceptor (D-A) structural engineering strategy may simultaneously improve both aspects of properties. Upon decorating a prototypical m-phenylene-linked TTM diradical (DR1) with electron-donating carbazole moieties, the functionalized molecule (DR2) exhibits a significantly enhanced PLQY from 3.1% to 18.8% at room temperature in the polymer matrix. Moreover, though both possess a triplet ground state enabled by a ferromagnetic spin exchange, the magneto-optical behaviors of DR1 and DR2 differ evidently. High-field magnetoluminescence measured from 0 to 50 T at varied temperatures reveals that DR1 emission is governed by the thermal population variations between the triplet ground state and singlet excited state, whereas the emission response of DR2 manifests more sophisticated field dependence, suggesting a nearly pure triplet emission of a complex spin-dynamic mechanism. Time-resolved EPR spectroscopy further proves that the carbazole-derived diradical preserves the capacity of spin-selective photo-initialization to the T0|0〉 sublevel of the ground state, and more impressively a considerably extended spin-polarization lifetime of 4.22 µs is exhibited by DR2, in comparison to 1.84 µs of DR1. These findings illustrate that electronic modulation through chemical modifications may serve as a powerful tool for tailoring the spin-optical interfaces of organic molecules to suit quantum information applications.