Hydrogen‐Bonded Two‐Component Ionic Crystals Showing Enhanced Long‐Lived Room‐Temperature Phosphorescence via TADF‐Assisted Förster Resonance Energy Transfer

Abstract

Molecular room‐temperature phosphorescent (RTP) materials with long‐lived excited states have attracted widespread attention in the fields of optical imaging, displays, and sensors. However, accessing ultralong RTP systems remains challenging and examples are still limited to date. Herein, a thermally activated delayed fluorescence (TADF)‐assisted energy transfer route for the enhancement of persistent luminescence with an RTP lifetime as high as 2 s, which is higher than that of most state‐of‐the‐art RTP materials, is proposed. The energy transfer donor and acceptor species are based on the TADF and RTP molecules, which can be self‐assembled into two‐component ionic salts via hydrogen‐bonding interactions. Both theoretical and experimental studies illustrate the occurrence of effective Förster resonance energy transfer (FRET) between donor and acceptor molecules with an energy transfer efficiency as high as 76%. Moreover, the potential for application of the donor–acceptor cocrystallized materials toward information security and personal identification systems is demonstrated, benefitting from their varied afterglow lifetimes and easy recognition in the darkness. Therefore, the work described in this study not only provides a TADF‐assisted FRET strategy toward the construction of ultralong RTP, but also yields hydrogen‐bonding‐assembled two‐component molecular crystals for potential encryption and anti‐counterfeiting applications.

Two-photon-excited ultralong organic room temperature phosphorescence by dual-channel triplet harvesting

“…To date, the ultralong TADF materials have been found in zeolite and ionic crystals, in which the rigid matrices suppress the vibrations. 29,30 Remarkably, the TADF lifetime of o-Cz is up to 0.79 s, which to the best of our knowledge is the longest lifetime reported amongst the pure organic TADF emitters under ambient conditions. Such a long lifetime validates the unique intra-and intermolecular interactions that suppress the nonradiative pathways.…”

Organic Room‐Temperature Phosphorescence with Strong Circularly Polarized Luminescence Based on Paracyclophanes

“…[1b] Meanwhile,the radiative and nonradiative decay from T 1 to S 0 also needs to be effectively suppressed to improve the phosphorescence efficiency. [7] There are several strategies in terms of molecular design to realize organic RTP: 1) Introducing the carbonyl units, [4,8] heteroatoms, [9] heavy atoms, [10] or resonance-induced spin flipping [11] to subsequently induce the strong spin-orbit coupling (SOC) effect, which contributes to higher k ISC ,r esulting in the larger population of triplet excitons;2 )effectively suppressing the non-radiative decay of low-lying triplet excitons through inhibiting the molecular nonradiative decay,e ither through crystallization, [12] one of the most commonly adopted methods; [13] or via halogenbonding, [14] intramolecular H-aggregation, [15] aromatic guest inclusion in supramolecular host, [16] and so on.…”

Organic Room‐Temperature Phosphorescence with Strong Circularly Polarized Luminescence Based on Paracyclophanes

“…Meanwhile, the radiative and nonradiative decay from T 1 to S 0 also needs to be effectively suppressed to improve the phosphorescence efficiency . There are several strategies in terms of molecular design to realize organic RTP: 1) Introducing the carbonyl units, heteroatoms, heavy atoms, or resonance‐induced spin flipping to subsequently induce the strong spin–orbit coupling (SOC) effect, which contributes to higher k ISC , resulting in the larger population of triplet excitons; 2) effectively suppressing the non‐radiative decay of low‐lying triplet excitons through inhibiting the molecular nonradiative decay, either through crystallization, one of the most commonly adopted methods; or via halogen‐bonding, intramolecular H‐aggregation, aromatic guest inclusion in supramolecular host, and so on.…”

“…Therefore, it is more common to observe the ultralong organic RTP in crystallized materials. Under these circumstances, however, most materials tend to rely heavily on multiple interactions between molecules within the crystal cell to restrict the molecular motions …”