Activating Molecular Room-Temperature Phosphorescence by Manipulating Excited-State Energy Levels in Poly(vinyl alcohol) Matrix

Abstract

Poly(vinyl alcohol) (PVA) has been found as a wonderful matrix for chromophores to boost their room-temperature phosphorescence (RTP) character by forming abundant hydrogen bonding. Despite the well-utilized protective effect, the constructive role in accelerating the intersystem crossing is less investigated. Here, we focus on its role in manipulating the excitedstate energy level to facilitate multiple intersystem crossing channels. Six benzoyl carbazole derivatives do not emit RTP in their solutions, powders, or crystals but exhibit significantly persistent RTP signals when embedded into the PVA matrix. Charge-transfer excited states were trapped by cofacial stacking in crystal, which blocks the intersystem crossing channels. In the PVA matrix, the allowed broad distribution of charge-transfer states covers the locally excited states, offering multiple intersystem crossing pathways via spin−vibronic orbit coupling. Consequently, efficient and persistent heavy-atom-free phosphors have been developed with the highest quantum yields of 7.7% and the longest lifetime of 2.3 s.

Achieving Colorful Ultralong-Lifetime Room-Temperature Phosphorescence Based on Benzocarbazole Derivatives through Resonance Energy Transfer

“…And on the other hand, the quenching of triplet excitons can be induced by the environmental medium. − Thus, the construction of an RTP system with ultralong emission lifetime is still a problem from both scientific research and practical applications desired to be solved. The realization of RTP is usually caused by the crystallization strategy, because the crystal state can provide an effective rigid environment to prevent the deactivation of the triplet state and inhibit the nonradiative transition process. − However, organic RTP crystalline materials as reported so far rarely exhibit ultralong lifetime (>1 s). − More importantly, compared with the preparation repeatability and machinability of crystal materials, amorphous RTP polymer materials are easy to process and have the characteristic of large-area preparation, which makes them more valuable in engineering applications. − Therefore, it is very significant to construct ultralong-lifetime amorphous RTP polymeric materials through sound coassembly strategies. − …”