Necessary and sufficient condition for organic room-temperature phosphorescence from host-guest doped crystalline systems.

Controlling and predicting the long-lived room temperature phosphorescence (RTP) from organic materials are the next challenges to address for the realization of new efficient organic RTP systems. Here, a new approach is developed to reach these objectives by considering host-guest doped crystals as well-suited model systems in that they allow the comprehensive understanding of synergetic structural interactions between crystalline host matrices and emitting guest molecules, one of the key parameters to understand the correlation between the solid-state organization and crystal RTP performances. We designed two series of sigma-conjugated donor/acceptor (D-sigma-A) carbazole-based matrices and isomeric 1H-benzo[f]indole-based dopants, capable of exploring a wide variety of conformations thanks to large rotational degrees of freedom provided by the sigma-conjugation. By correlating results of single-crystal X-ray diffraction analysis and photoluminescence properties, we established a necessary and sufficient condition for RTP that paves the way for the development of new long-lived RTP host-guest doped systems.