Molecular-Level Understanding of Dual-RTP via Host-Sensitized Multiple Triplet-to-Triplet Energy Transfers and Data Security Application

Dual-room-temperature
phosphorescence (DRTP) from organic molecules
is of utmost importance in chemical physics. The Dexter-type triplet-to-triplet
energy transfer mechanism can therefore be used to achieve DRTP at
ambient conditions. Here, we report two donor–acceptor (D–A)-based
guests (CQN1, CQN2) in which the donor (D)
and acceptor (A) parts are held in angular orientation around the
C–N single bond. Spectroscopic analysis along with computational
calculations revealed that both guests are incapable of emitting either
thermally activated delayed fluorescence (TADF) or RTP at ambient
conditions due to large singlet–triplet gaps, which are presented
to show host (benzophenone, BP)-sensitized DRTP via multiple intermolecular triplet-to-triplet energy transfer (TTET)
channels that originate from the triplet state (T1BP) of BP to the triplet states
(T1D, T1A) of the D and
A parts (TTET-I:T1BP → T1D; TTET-II:T1BP → T1A). In addition, an intramolecular TTET channel that occurs
from the T1D to T1A states
of the D and A parts of CQN2 is also activated due to
the low triplet (T1D)–triplet (T1A) gap at ambient conditions. The efficiency
of TTET processes was found to be 100%. The phosphorescence quantum
yields (ϕP) and lifetimes (τP) were
shown to be 13–20% and 0.48–0.55 s, respectively. Given
the high lifetime of the DRTP feature of both host–guest systems
(1000:1 molar ratio), a data security application is achieved. This
design principle provides the first solid proof that DRTP via radiative decay of the dark triplet states of the D
and A parts of D–A-based non-TADF systems is possible, revealing
a method to increase the efficiency and lifetime of DRTP.