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

Poly(vinyl alcohol) (PVA) has been found as a wonderfulmatrixfor chromophores to boost their room-temperature phosphorescence (RTP)character by forming abundant hydrogen bonding. Despite the well-utilizedprotective effect, the constructive role in accelerating the intersystemcrossing is less investigated. Here, we focus on its role in manipulatingthe excited-state energy level to facilitate multiple intersystemcrossing channels. Six benzoyl carbazole derivatives do not emit RTPin their solutions, powders, or crystals but exhibit significantlypersistent RTP signals when embedded into the PVA matrix. Charge-transferexcited states were trapped by cofacial stacking in crystal, whichblocks the intersystem crossing channels. In the PVA matrix, the allowedbroad distribution of charge-transfer states covers the locally excitedstates, offering multiple intersystem crossing pathways via spin-vibronicorbit coupling. Consequently, efficient and persistent heavy-atom-freephosphors have been developed with the highest quantum yields of 7.7%and the longest lifetime of 2.3 s.

Automated summary

Poly(vinyl alcohol) (PVA) is used as a matrix to enhance the room-temperature phosphorescence (RTP) of chromophores by forming abundant hydrogen bonding. The role of PVA in manipulating the excited-state energy level to facilitate multiple intersystem crossing channels is investigated. The PVA matrix allows a broad distribution of charge-transfer states, providing multiple pathways for intersystem crossing via spin-vibronic orbit coupling. Consequently, heavy-atom-free phosphors with high quantum yields (7.7%) and long lifetime (2.3 s) have been developed.