Controlling luminescence behaviors of organic chromophores is essential for their applications. As emissions from chromophores are strongly modulated by structural fluctuations and external environments, their comprehensive understandings remain elusive. Here, we demonstrate the modulation of the photophysics of benzophenone (Bzp), a prototypical triplet sensor molecule, by encapsulating it into mesoporous silica nanomaterials (MSNs). We systematically probed photoluminescence property modulation using time-resolved photoluminescence (TR-PL) measurements. The strong confinement effect on Bzp in MSN heavily modifies the excited-state properties. A long-lived emission (40 μs) from the simplest organic chromophore was observed after host-guest complexation, and photoluminescence of Bzp is controlled with the host's framework structures. We analyzed temperature-dependent TR-PL behaviors and revealed that a host matrix induced thermally activated delayed fluorescence (TADF) from Bzp in the host-guest (Bzp:MSN) complex. The host-guest complexation efficiently suppresses intramolecular motions and significantly alters the singlet-triplet energy gap (ΔEST) to a sufficiently small value (<60 meV) and leads to efficient reverse intersystem crossing.
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