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

Abstract

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.