Fig. 5: Spin–optical interface in diradicals.
a, X-band ESR conditions (9.7 GHz, 0.346 T) ΔPL/PL >10−3% at 100 K. We probe the spin–optical interface using probed using PLDMR spectra. ODMR, optically detected magnetic resonance; fMW, frequency of the applied microwave. b, The spectrally resolved PLDMR under conditions at the PLDMR resonance point at 4.1835 T. All PL detected in a–c and utilized a long-pass filter (>420 nm) to cut-off the laser line. APD, avalanche photo-diode; MW-ON, microwave on; MW-OFF, microwave off. c, An illustration of the proposed spin-selective ISC mechanism for the observed PLDMR behaviour. At Bz > 0.7 T and T < 0.8 K the ms = −1 sublevel in the ground state triplet is occupied, which has a small ISC probability. Bz is the static magnetic field applied along the z-axis. When microwaves are switched on (right), a microwave-induced Δms = 1 transition drives population from ms = −1 to ms = 0 within the ground state. This ms = 0 sublevel has a higher probability for ISC in the excited state, which leads to more singlet PL and reduced triplet PL, manifest as a large PLDMR contrast. The samples for a were thin films made with 0.1 wt% M2TTM-3Flr-M2TTM doped into polystyrene, and in b, we doped 10 nM of M2TTM-3Flr-M2TTM into PhCl3 crystal. The crystals were prepared using slow evaporation of a solution, which were subsequently washed and polished, as described in Supplementary Information Section 13.
