Strategies for developing purely
organic materials exhibiting both
high efficiency and persistent room-temperature phosphorescence (RTP)
have remained ambiguous and challenging. Herein, we propose that introducing
an intermediate charge transfer (CT) state into the donor–acceptor
binary molecular system holds promise for accomplishing this goal.
Guest materials showing gradient ionization potentials were selected
to fine-tune the intermolecularly formed CT state when doped into
the same host material with a large electron affiliation potential.
Such a CT intermediate state accelerates the population of the triplet
exciton to benefit phosphorescent emission and decreases the phosphorescence
lifetime via quenching the long-lived triplet excitons. As a result,
a “trade-off” between a long phosphorescence lifetime
(595 ms) and a high phosphorescent quantum yield (27.5%) can be obtained
by tuning the host–guest energy gap offset. This finding highlights
the key role of CT in RTP emission and provides new guidance for developing
novel RTP systems.