Probing the design rules for densely packed organic triplet media for spin-based quantum devices

Spin-based quantum technologies have the advantage of employing chemical media with tuneable properties linked to their molecular structure. A principal objective of this field of research is to enhance photoexcited spin yields and spin relaxation parameters to optimize their controllability. A near-term benefactor of this work would be quantum sensors based on masers, the microwave analogue of the laser. In this study, we synthesize a series of novel charge transfer co-crystals with 1,2,4,5-tetracyanobenzene (TCNB) and chemically modified donor molecules, namely, acetylation of anthracene, and investigate their relevant optical and triplet spin dynamics to elucidate the important design principles for engineering future quantum spin materials. We found the degree and position of acetylation controlled the degree of charge transfer and by extension their optical band gap. Furthermore, we determined that while the magnitude of spin polarisation in the triplet state was generally slightly smaller than the prototypical Anthracene:TCNB, the spin-lattice relaxation and spin coherence times were significantly improved by more than a factor of two. Altogether, we find that the acetylanthracene co-crystals exhibit improved maser potential and that acetylation could be a powerful synthetic tool for the realization of masers with lower pump energy thresholds and quantum materials.