Room-temperature optically detected magnetic resonance of triplet excitons in a pentacene-doped picene single crystal

The inclusion of functional molecules as substitutional dopants in single crystals of organic hosts with complementary optical properties provides a versatile strategy to tune optical and magnetic properties in view of their applications in opto-electronics and spintronics. Here, by combining electron spin resonance and optical spectroscopy, isolated triplet exciton states with distinct emission and absorptive resonance modes from two magnetically inequivalent sites of pentacene within the picene crystal are detected at room temperature. This is possible due to the incorporation of a low-doping, 1% mol/mol of pentacene into the monoclinic polymorph of picene high-quality single crystals. In addition, delayed fluorescence—optically detected magnetic resonance (ODMR) studies demonstrate efficient spin-dependent optical activities that are tuned by crystallographically oriented magnetic fields. These properties are particularly appealing for the exploitation of pentacene in room-temperature spin-driven opto-electronics, quantum sensing and in microwave amplification by stimulated emission of radiation (MASER). Graphical abstract: Triplet excitons of pentacene molecules doped into a picene single crystal provide microwave emission and absorptive resonance modes as well as large optically detected magnetic resonance contrast which can be tuned by magnetic field strength and direction. These properties make pentacene-doped picene single crystals promising materials for spin-driven opto-electronics and, in particular, in microwave amplification by stimulated emission of radiation (MASER). [Figure not available: see fulltext.]