Triplet energy harvesting via either thermally activated delayed fluorescence (TADF) or room-temperature phosphorescence (RTP) from pure organic systems has attracted great attention in the field of organic light-emitting diodes, sensing, and bioimaging. However, the realization of dual electroluminescence via TADF and RTP in single molecules remains elusive. Herein, we report two phenoxazine-quinoline conjugates (DPQ and DPQM) in which two phenoxazine donors are covalently attached to the 6,8-positions of 2,4-diphenylquinoline and/or 7-methyl-2,4-diphenylquinoline acceptors. Experimental and quantum chemistry calculations combining reference compounds ( o-PQP, p-PQP, Phox, and QPP) reveal that both conjugates show TADF (with different rate constants of reverse intersystem crossing, k rISC = 0.43–1.30 × 106 s–1) via reverse intersystem crossing from the charge transfer triplet (3CT) to singlet (1CT) states mediated by vibronic coupling among 1CT, local triplet (3LE), and 3CT states due to close energy gaps. Further, RTP with quantum yields (ϕP) of ca. 21–24% features was also observed due to the radiative decay of 3LE states. Phosphorescence measurements of DPQM at low temperatures (T = 77, 10 K) ensure a distinct zero-field splitting of T 1(CT) into substates. Both compounds showed dual electroluminescence with external quantum efficiencies of ca. 11–12% due to the efficient triplet harvesting from both TADF and RTP channels.

White light emission (WLE) from multicomponent organic systems has attracted significant attention in recent years due to easy access of bright blue and yellow/orange, or red emitters. However, realizing WLE from a single emissive layer of multicomponent organic thermally activated delayed fluorescence (TADF) systems is an exasperating task due to uncontrolled Förster energy transfer and Dexter-type triplet–triplet energy transfer (TTET). To address this issue, we demonstrated WLE using blend films (WL1, WL2, and WL3) of blue (CPPN, CQ, and DMOC-DPS) and orange (PTzQ) TADF emitters. WL1 comprises CPPN and PTzQ, while DMOC-DPS and PTzQ were used to construct WL2. Spectroscopic analysis revealed that WL1 and WL2 exhibited dual emission features (quantum yields = 48–54%; Commission Internationale de l’éclairage coordinates: 0.34, 0.31; 0.31, and 0.34) via simultaneous blue- and orange-TADF covering the visible region. The WLE feature is observed due to (i) similar absorption and different Stokes shifted emission color of both the emitters and (ii) the absence of TTET caused by large triplet–triplet gaps (>0.4 eV) between the emitters. In contrast, WLE via fluorescence and TADF was observed in WL3 due to TTET. This finding is expected to provide new insights for designing high-energy-efficient WLE for white organic light-emitting diodes.

Room-temperature phosphorescence (RTP) from organic compounds has attracted increasing attention in the field of data security, sensing, and bioimaging. However, realization of RTP with an aggregate induced phosphorescence (AIP) feature via harvesting supersensitive excited charge transfer triplet ( 3 CT) energy under visible light excitation (VLE) in single-component organic systems at ambient conditions remains unfulfilled. Organic donor–acceptor (D–A) based orthogonal structures can therefore be used to harvest the energy of the 3 CT state at ambient conditions under VLE. Here we report three phenoxazine–quinoline conjugates (PQ, PQCl, PQBr), in which D and A parts are held in orthogonal orientation around the C–N single bond; PQCl and PQBr are substituted with halogens (Cl, Br) while PQ has no halogen atom. Spectroscopic studies and quantum chemistry calculations combining reference compounds (Phx, QPP) reveal that all the compounds in film at ambient conditions show fluorescence and green-RTP due to (i) radiative decay of both singlet charge transfer ( 1 CT) and triplet CT ( 3 CT) states under VLE, (ii) energetic nondegeneracy of 1 CT and 3 CT states ( 1 CT– 3 CT, 0.17–0.21 eV), and (iii) spatial separation of highest and lowest unoccupied molecular orbitals. Further, we found in a tetrahydrofuran–water mixture ( f w = 90%, v/v) that both PQCl (10 –5 M) and PQBr (10 –5 M) show concentration-dependent AIP with phosphorescence quantum yields (ϕ P ) of ∼25% and ∼28%, respectively, whereas aggregate induced quenching (ACQ) was observed in PQ. The phosphorescence lifetimes (τ P ) of the PQCl and PQBr aggregates were shown to be ∼22–62 μs and ∼22–59 μs, respectively. The ϕ P of the powder samples is found to be 0.03% (PQ), 15.6% (PQCl), and 13.0% (PQBr), which are significantly lower than that of the aggregates (10 –5 M, f w = 90%, v/v). Film (Zeonex, 0.1 wt %) studies revealed that ϕ P of PQ (7.1%) is relatively high, while PQCl and PQBr exhibit relatively low ϕ P values (PQCl, 9.7%; PQBr, 8.8%), as compared with that of powder samples. In addition, we found in single-crystal X-ray analysis that multiple noncovalent interactions along with halogen···halogen (Cl···Cl) interactions between the neighboring molecules play an important role to stabilize the 3 CT caused by increased rigidity of the molecular backbone. This design principle reveals a method to understand nondegeneracy of 1 CT and 3 CT states, and RTP with a concentration-dependent AIP effect using halogen substituted twisted donor–acceptor conju...