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.

A simple, efficient, green, and cost-effective procedure has been developed for the synthesis of dihydropyrimidinones by a solvent-free and catalyst-free Biginelli's condensation of 1,3dicarbonyl compound, aldehyde, and urea. This approach of direct reaction in neat without solvent and catalyst shows a new direction in green synthesis.

No abstract

No abstract

Understanding the local triplet (3LE), charge transfer triplet (3CT), and charge transfer singlet (1CT) is of great importance in designing thermally activated delayed fluorescence (TADF) and room‐temperature phosphorescence (RTP) materials for their use in organic light‐emitting devices (OLEDs), sensing, and bioimaging. Herein, two phenothiazine–quinoline conjugates (PTzQ1, PTzQ2) in which the donor (PTz) and acceptor (Q1, Q2) parts are held in near‐orthogonal orientation that gives rise to spatial separation of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) are reported. Photophysical studies of both conjugates along with their individual components (PTz, Q1, Q2) show that TADF occurs via reverse intersystem crossing (rISC) from the upper‐level local triplet (3LE) to lower‐level singlet 1CT mediated by vibronic coupling between 3LE and 3CT, whereas RTP is realized from 3LE. It is found that all three excited states are close in energy, 0.16–0.19 eV (3LE−1CT), 0.02–0.03 eV (1CT−3CT), and 0.14–0.16 eV (3LE−3CT) with the order of 3LE > 1CT > 3CT. Both conjugates exhibit a high rate constant of rISC (krISC, 7.9–9.7 × 105 s−1), resulting in external quantum efficiency (EQE) values of ≈4.7% (solution processed) with emission from both RTP and TADF components.