Pachaiyappan Rajamalli

An in‐depth understanding of locally excited (LE) intermediate states is crucial in regulating the reverse intersystem crossing (RISC) process and overall efficiency of thermally activated delayed fluorescence (TADF) emitters, directing rational material synthesis. Herein, we investigated the effect of incorporating a low‐triplet‐energy naphthyl core at the acceptor, donor, and both positions through the design and synthesis of three donor‐acceptor (D‐A) emitters, with tunable optoelectronic properties. Doping 7 wt.% of NP‐ m DPA, 3BPy‐ m PNP, and NP‐ m PNP in 3,3′‐di(9 H ‐carbazol‐9‐yl)‐1,1′‐biphenyl ( m CBP) host resulted in the first excited singlet‐triplet energy gap (Δ E _ST ) of 0.28, 0.31, and 0.42 eV. Temperature‐dependent transient photoluminescence (PL) measurements indicate robust TADF behavior in NP‐ m DPA and 3BPy‐ m PNP, while NP‐ m PNP exhibits weaker TADF accompanied by prominent phosphorescent fingerprints. In multi‐layer organic light‐emitting diodes (OLEDs) with an emissive layer (EML) comprising 7 wt.% of emitters in m CBP host, NP‐ m DPA exhibited an electroluminescence (EL) peak at 502 nm with the highest maximum external quantum efficiency (EQE _max ) of 18.6%. In contrast, 3BPy‐ m PNP (505 nm) and NP‐ m PNP (492 nm) showed reduced EQE _max of 12.6% and 5.1%. Detailed theoretical calculations reveal that incorporating a naphthyl unit in both D and A produces intermediate LE triplet states and improves RISC. Whereas, the naphthyl unit in only D or only A results in reduced Δ E _ST and , enabling NP‐ m DPA to be the most efficient among the studied emitters.

For next‐generation organic light‐emitting diode (OLED) displays and lighting, achieving stable, efficient deep‐blue and sky‐blue emission remains a challenge. Herein, we report a cyanopyridine‐based modular scaffold, an asymmetric dual core (2tCz2PyCN) that suppresses exciton loss to achieve sky‐blue emission, and an asymmetric single core analog (2tCzPyCN). The single core 2tCzPyCN exhibits deep blue emission ( λ _max = 437 nm) with a CIE of (0.15, 0.14), asymmetric 2tCz2PyCN emitter exhibits sky‐blue emission ( λ _max = 478 nm) with a CIE of (0.19, 0.38). The reduced conjugation in the single core 2tCzPyCN widens the energy gap, resulting in deep‐blue color (CIE _y = 0.14), it also maximizes faster reverse intersystem crossing (RISC) through spin orbit coupling (SOC). The extended bipyridine core of 2tCz2PyCN lowers the excited state reorganization energy (0.82 vs. 0.94 eV), suppressing non‐radiative decay and raising the PLQY from 41.6% to 80.7%. The 2tCzPyCN‐based device achieves an EQE _max of 8.80% in the deep blue region, whereas the asymmetric 2tCz2PyCN shows EQE _max of 16.63% in the sky‐blue region. This work demonstrates that engineering the excited state via an asymmetric acceptor is a practical pathway for color tuning and developing efficient TADF emitters.

We report the synthesis, photophysical properties, and electroluminescent performance of a Ir(3-phenylisoquinoline)3 (Ir(3-piq)3) complex. Single-crystal X-ray analysis reveals a distorted octahedral geometry with strong intermolecular interactions that enforce rigid molecular packing and abate nonradiative decay by reducing structural reorganization. Photophysical investigations reveal weak orange emission in solution and significantly enhanced emission in doped films. Optimized organic light-emitting diodes (OLEDs) achieve a low turn-on voltage of 2.5 V, a maximum external quantum efficiency (EQEmax) of 22.8%, and a brightness of 49616 cd/m2 with stable electroluminescence. Moreover, hybrid white OLEDs were fabricated by incorporating the blue TADF emitter, 3DPy-pDTC as an auxiliary dopant. The fabricated devices exhibit warm-white emission at 0.7 wt % doping of Ir(3-piq)3, delivering EQEmax of 17.7%. Notably, reducing the doping concentration of Ir(3-piq)3 to 0.5 wt % results in a well-balanced bright white emission with CIE co-ordinate of (0.29, 0.33) and achieves an EQEmax of 14.7%. These performances are attributed to efficient exciton utilization driven by synergistic phosphorescence and rapid reverse intersystem crossing in TADF emitters. Overall, this work demonstrates an effective strategy for achieving high-efficiency and stable orange emission in Ir-complexes and color-tunable hybrid white OLEDs through synergistic exciton management.

Owing to their inherently helical π-conjugated frameworks, helicenes are considered promising candidates for circularly polarized luminescence (CPL). Nonetheless, their implementation in circularly polarized organic light-emitting diodes (CP-OLEDs) remains limited due to difficulties in achieving both high color purity and external quantum efficiency (EQE). Recent advancements incorporate multi-resonance properties with boron-nitrogen units, which have shown significant improvements in this regard. Herein, a chiral emitter ( C ₁ ) consisting of 1,4-B,N-embedded helical configuration is studied. C ₁ exhibits narrowband fluorescence emission at 510 nm with a full width at half maxima (FWHM) of 23 nm in toluene and 26 nm in thin film. The resolved enantiomers show symmetric CPL, with a dissymmetry factor ( g _lum ) of 1.0 × 10 ^–3 . The solution-processed CP-OLED based on C ₁ exhibits external quantum efficiency (EQE) of 5.3%, delivering bright green emission centred at 514 nm with a FWHM of 28 nm. To further enhance the performance of the device, hyperfluorescent (HF) OLEDs are fabricated with C ₁ acting as a terminal emitter and BPy-DTC as the TADF sensitizer. The maximum EQE of 13.5% is achieved, with a narrow FWHM of 39 nm. This work highlights the strong potential of helicene-based emitters for application in narrowband CP-OLEDs.

In this work, we report the strategic incorporation of a rigid 14H‐dibenzo[a,j]xanthene ( DBX ) core into the BCz‐BN framework, leading to the development of a novel DBX‐BCz‐BN multi‐resonance (MR) thermally activated delayed fluorescence (TADF) emitter. This structural modification preserves the sky‐blue emission color while substantially narrowing the emission profile, reducing the full width at half maximum (FWHM) to 17 nm. In addition, the singlet–triplet energy gap (Δ E _ST ) is lowered from 0.17 eV for BCz‐BN to 0.06 eV, thereby promoting more efficient reverse intersystem crossing (RISC) and improved exciton harvesting. As a result, the corresponding OLED device based on DBX‐BCz‐BN exhibits an external quantum efficiency (EQE) of 22.2%, while maintaining the same emission color. These results demonstrate that rigid‐core engineering via DBX incorporation is an effective strategy for achieving narrowband, efficient, and color‐pure sky‐blue TADF emitters.

Bridged oxo/thioethers are conjugated to a highly twisted molecular framework where alterations of the heteroatoms result in various molecular packing patterns, tuning blue-to-red emission, and are applied to afford a solution-processed yellow OLED.

Highly efficient white organic light-emitting diodes (WOLEDs) created by combining phosphorescent and thermally activated delayed fluorescence (TADF) emitters have advanced rapidly as cutting-edge technology for their potential applications in flat-panel displays and solid-state lighting. However, achieving high device performance while simultaneously ensuring a high white color quality remains a challenge. Here, we demonstrate efficient WOLEDs, fabricated by using a blue TADF emitter with an orange phosphor in a single emissive layer, enabling the generation of white light. The WOLEDs exhibit outstanding electroluminescent (EL) performance, achieving a maximum external quantum efficiency (EQE) of 31.8% and power efficiency (PE) of 56.8 lm W^-1 and producing cold and warm white light by varying the concentration of the phosphor emitter. To further enhance the quality of white light without compromising the EL performance, a multilayer sandwich configuration was adopted by introducing an ultrathin (∼1 nm) layer of the efficient green TADF emitter BPyDTC between two white emissive layers. This design strategy resulted in a high-performance WOLED with a maximum EQE of 28.8% and a PE of 65.5 lm W^-1, with EQE and PE values of 17.0% and 25.1 lm W^-1at a luminance of 1000 cd m^-2, respectively. The emission from all the layers effectively blends, achieving better coverage of the visible spectrum and generating white light with Commission Internationale de l'Eclairage, CIE coordinates of (0.38, 0.41).

Ultra-deep blue fluorescent emitters with Commission Internationale de L’Eclairage (CIE _y ) < 0.08 are still in demand for achieving vibrant full-color displays.

A novel dual core TADF emitter has been synthesized involving a symmetric coupling, demonstrating a minimal Δ E _ST of 0.08 eV, an enhanced PLQY of 59.1% and a high EQE _max of 15.02%, when compared to its single-core counterpart.

Modification of the molecular structure can drastically change the photophysical properties of the luminogens, establishing these structure-property relationships provides a roadmap for the rational design of novel materials. In this...