Transformation from Nonlasing to Lasing in Organic Solid-State through the Cocrystal Engineering

Organic semiconductor molecules that ideally suitable for being used to achieve solid-state lasers (OSSLs) in aggregate-state cannot actually act as the efficient laser gain materials due to varieties of nonradiative pathways, which consume the energy of excited state. Herein, we elaborately utilized a cocrystal approach to achieve the transformation of 1,4-bis(2-cyanostyryl)benzene (o-BCB) microcrystals from nonlasing to lasing. The tightly packed o-BCB molecules in the crystal leads to the formation of excimer state, hindering the population inversion even at the maximum tolerable pump density of 20.2 mu J/cm(2). Impressively, the formation of the o-BCB-4-bromo-2,3,5,6-tetrafluorobenzoic acid (BFC) cocrystal eliminates the excimer and then forms the pure four-level energy system, which contributes to the occurrence of the room-temperature blue lasing at 450 nm with a threshold of 4.4 mu J/cm(2). Our demonstration proves that this cocrystal engineering strategy can extend the molecular system for OSSLs.