Herein, a simple aza-aromatic compound dibenzo[a,c]phenazine (DPPZ), which exhibits single-molecule white light with a ternary emission, consisting of simultaneous fluorescence (S 1 →S 0 ) and dual room-temperature phosphorescence (RTP, T 2 →S 0 and T 1 →S 0 ) is reported. The Commission Internationale de l' Éclairage coordinates of DPPZ powder are (0.28, 0.33). To everyone's knowledge, this is the first case to achieve single-molecule white emission with ternary emission of fluorescence and dual RTP. This finding provides a prototype strategy to realize low-cost, stable pure organic singlemolecule white light emission with three standard primary colors through further precise modulation of excited states.

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Multi-resonance TADF (MR-TADF) emitters are promising for high-resolution OLEDs, but the concurrent optimization of excited-state dynamics and color purity remains a tough challenge. Herein, three deep-blue MR-TADF compounds (BN1-BN3) featuring gradually enlarged ring-fused structures and increased rigidity are accessed by lithiumfree borylation in high yields from the same precursor, with all the emitters possessing CIE y coordinates below 0.08. Structure-property investigations demonstrate a strategic improvement of the oscillator strength (f osc ) and acceleration of the reverse intersystem crossing (RISC) process by extending the π-skeleton, where BN3 realizes a maximum external quantum efficiency (EQE) of 37.6 % and reduced roll-off, thus showing the best efficiency reported for deep-blue TADF OLEDs. The internal regulation of the efficiency and color purity of these compounds validate the general effectiveness to achieve advanced deep-blue narrowband emitters with higher-order boron/nitrogen-based MR motifs.

Polyaromatic compounds are significant members of leading candidates for organic semiconductors and optical materials. However, a thorny problem of polyaromatic materials is that their good emissive abilities in solutions are seriously weakened in solids due to strong π−π interactions between aromatics. As a typical case, the intermolecular π−π interaction tends to form excimers for polyaromatic system, which were always considered to quench fluorescence and decrease luminous efficiency in the past decades. Herein, anthracene is modified by meta-substituted bromobenzene to facilitate the formation of discrete dimeric stack in solids, leading to the enhanced anthracene excimer fluorescence. Particularly, instead of excimer quenching fluorescence, the more anthracene dimers in solids, the higher fluorescence efficiency, namely, excimer-induced enhanced solid-state emission. This work not only provides a meta-substituted strategy for molecular design to form excimer in solids but also demonstrates that high-efficiency solid-state emission can be achieved by excimer species.

light-emitting diodes (OLEDs) due to their low production-cost as well as the capability to harvest "dark" triplet excitons via a reverse intersystem crossing (RISC) mechanism. [1][2][3][4] Facilitating of RISC is made by reduction of the energy gap (ΔE ST ) between the lowest excited singlet and triplet (S 1 and T 1 ) states, typically achieved in twisted donor-acceptor (D-A) typed molecules with separated frontier molecular orbitals (FMOs) at the expense of low oscillator strength (f) and photoluminescence quantum yield (Φ PL ). [5][6][7][8] This contradiction undoubtedly sets an obstacle to obtain highly efficient emitter, and the large structural reorganization occurred in the excited state would cause broad emission spectra and increased non-radiative decay channels, eventually weakening the performances of corresponding devices. [9][10][11][12][13][14][15] Instead of the conventional D-A configured emitters, a unique category of multi-resonance TADF (MR-TADF) molecules based on fused polycyclic aromatics was lately proposed by Hatakeyama et al. to mitigate the aforementioned issues. [16][17][18][19][20][21][22] The complementary resonance effects of electrondeficient B and electron-rich N/O atoms within the framework separates the FMOs to induce short-range charge-transfer (SR-CT), concurrently offering a small ΔE ST and a high radiative decay rate (10 7 -10 8 s −1 ) from S 1 to ground (S 0 ) state. [17,23] The planar nature with high rigidity guaranteed narrow full width at half maximum (FWHM) emissions, and could also induce favorable horizontal dipole orientation of the emitters to boost optical out-coupling efficiency. [24] Thus far, the majority of the blue MR-TADF emitters were constructed from the basic motif DABNA (Scheme 1) due to synthetic feasibility and their decent quantum efficiencies. [25] Replacement of the diphenylamino subunits into carbazolyl-derived BN-CZ as a new core skeleton with bathochromic emission, which was adopted to realize full-color electroluminescence (EL) with high color purity and maximum external quantum efficiencies (EQE max s) above 20% by peripheral electronic modulation. [24,[26][27][28][29] Nonetheless, most MR-TADF devices encountered severe triplet-related efficiency loss at high luminance/current density stemmed from the intrinsic structural planarity and long-delayed lifetime, and relied on the involvement of sensitizing host to avoid triplet Multi-resonance thermally activated delayed fluorescence (MR-TADF) offers an exceptional solution for narrowband organic light-emitting diode devices in terms of color purity and luminescence efficiency, while the development of new MR skeleton remains an exigent task. It is hereby demonstrated that a simple modification of the B (boron)−N (nitrogen) framework by sp 3 -carbon insertion will significantly bathochromic shift the short-range charge-transfer emission, boost the reverse intersystem crossing process, and improve the device performances. The bis(acridan)phenylene-based skeleton developed in this contribution presen...

Revealing the photoluminescence (PL) origin and mechanism is a most vital but challenging topic of carbon dots. Herein, confined-domain crosslink-enhanced emission (CEE) effect was first studied by a well-designed model system of carbonized polymer dots (CPDs), serving as an important supplement to CEE in the aspect of spatial interactions. The “addition-condensation polymerization” strategy was adopted to construct CPDs with substituents exerting different degrees of steric hindrance. The effect of confined-domain CEE on the structure and luminescence properties of CPDs have been systematically investigated by combining characterizations and theoretical calculations. Such tunable spatial interactions dominated the coupling strength of the luminophores in one particle, and eventually resulted in the modulated PL properties of CPDs. These findings provide insights into the structural advantages and the PL mechanism of CPDs, which are of general significance to the further development of CPDs with tailored properties.

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