Masashi Mamada

Organic near‐infrared (NIR) luminophores are attractive for a wide range of applications owing to the unique advantages of organic materials. However, the development of efficient NIR emitters remains challenging because nonradiative decay rate constant ( k _nr ) increases rapidly with decreasing excited‐state energy according to the energy‐gap law. In this work, we developed a molecular design strategy that integrates rigid boron‐fused polycyclic framework derived from multiple‐resonance (MR) chemistry into a narrow‐gap molecular framework to suppress electron–vibration coupling and structural relaxation in the excited state. The resulting emitters exhibited reduced k _nr s, enhanced photoluminescence quantum yields, and higher external electroluminescence quantum efficiencies in NIR organic light‐emitting diodes relative to a conventional donor‐based analogue. Furthermore, these materials showed amplified spontaneous emission at wavelengths above 900 nm with significantly low thresholds, despite the difficulty of achieving efficient organic gain media in this spectral region. These results demonstrate that the incorporation of rigid MR‐derived framework is a promising strategy for controlling nonradiative losses and improving both efficient spontaneous and stimulated emission characteristics, providing a basis for the development of organic NIR materials.

Spontaneous emission is inherently associated with spectral broadening mechanisms, resulting in finite bandwidth in the emitted light. Narrowing this linewidth toward the monochromatic limit has long been a central pursuit in photonics, as it determines the ultimate color purity of nonstimulated light sources. Organic luminescent materials offer facile wavelength tunability but typically exhibit broad emission bands (>40 nanometers). The emergence of multiple-resonance emitters has provided a promising route to overcome this limitation, yet most reported systems remain within 20 to 30 nanometers. We present a molecular design strategy that amplifies the multiple-resonance effect through molecular repetition, yielding fluorescence with linewidths of 6.9 nanometers in toluene, 5.5 nanometers in 3-methylpentane, and 9.1 nanometers in a doped polymer film, placing this molecular framework among the narrowest-band organic luminophores reported.

Removing reactive olefin linkers creates more photostable organic laser chromophores with enhanced optical gain, increased emission cross-sections, and ultra-low violet/deep-blue ASE thresholds via a simple and scalable molecular design.

Peri-fused PAHs converge to a single localized representation: cata-condensation increases aromatic sextets and amplifies brightness while linear extension adds cis -diene units and diminishes it.

Recent studies on acenes have highlighted a localized representation (LR) of the aromatic sextets, challenging Clar’s classical model of migrating sextets. Here we extend this framework to peri-fused systems by investigating bis(tri-isopropylsilyl)ethynyl (TIPS)-functionnalized polycyclic aromatic hydrocarbons (TIPS-PAHs) namely TIPS anthanthrene (TIPS-ATT), TIPS pyranthrene (TIPS-PYR) and TIPS dibenzo[pyranthrene] (TIPS-DBPYR) as test beds for LR. Crystal structures provide direct evidence for determining the Fries canonical structures, with bond lengths and bond length alternation (BLA) at the zig zag edge offering robust criteria for positioning aromatic sextets. While NICS and HOMA indices are broadly consistent with these assignments, their interpretation should be considered with some caution. Optical studies reveal progressive bathochromic shifts (491–599 nm) with increasing conjugation, but absorption strength and fluorescence quantum yield depend critically on the mode of π extension: catacondensation enhances brightness, whereas linear extension diminishes it. Remarkably, TIPS-PYR combines a record molar absorption coefficient (>200,000 M⁻¹·cm⁻¹) with high fluorescence quantum yield (ΦF = 0.93), yielding a molar brightness comparable to giant nanoribbons. Stability assays show that TIPS-ATT and TIPS-PYR are bench stable, whereas TIPS-DBPYR, despite reduced fluorescence efficiency, exhibits enhanced photostability relative to TIPS pentacene (TIPS-PEN) and satisfies the energetic criterion for singlet fission. These findings establish LR as a robust framework for describing peri fused PAHs, identify TIPS-PYR as an exceptionally bright dye, and position TIPS-DBPYR as a promising singlet fission material.

Fully green synthesis and alcohol processing enable the first solution-processed MMLCT Pt( ii ) OLEDs, demonstrating efficient electroluminescence (EQE ≈ 14% and max. brightness of 8500 cd m ⁻² ) from highly aggregated neat emissive films.

Organic light‐emitting diodes (OLEDs) have achieved remarkable commercial success in displays for mobile phones and televisions, while blue OLEDs still have a drawback in triplet utilization. Hyperfluorescence OLEDs utilizing thermally activated delayed fluorescence (TADF) represent a promising technology for achieving high efficiency and color‐purity. However, their overall performance, including device durability, remains significantly below industrial requirements. In particular, one still has to face the lack of understanding of the relationship between the photophysical properties of TADF materials and their stability. To date, many studies have suggested that shorter exciton lifetimes, which suppress annihilation processes, can help enhance device lifetimes. In this work, however, the correlation between device lifetime and the photophysical properties of four TADF emitters is investigated and find a noticeable decrease in stability with increasing excited‐state energy levels, indicating that higher excited‐state energies (S₁+T₁ energies > 5.4 eV) have a substantial impact on device degradation. While improved color purity can be achieved by using a TADF assistant dopant with a shorter emission wavelength, the energy levels must be confined within a specific range to balance efficiency and device lifetime effectively. This study provides practical guidelines for improving device stability and performance.

Recent advances in materials development for organic light‐emitting diodes (OLEDs) have been driven by an emerging design concept known as multiple‐resonance (MR), which provides the benefits of high efficiency and color purity required for commercial OLED displays. Borylation reaction constructing MR frameworks is a key step for developing new π‐conjugated systems, while this reaction includes the limitation of selectivity, making it challenging to control reactions in elaborate molecular structures. Although a wide variety of MR compounds have been prepared through carefully planned synthetic schemes based on retrosynthetic analysis, these tasks typically require significant effort for each individual target. Herein, we demonstrate a successful late‐stage functionalization strategy that enables structural modifications after the borylation reaction, especially in hardly accessible regions in MR structures via carbon–nitrogen bond cleavage. Our new synthetic method also allows access to new products which were never feasible before. The newly developed material, DABNA‐dimer , proves the impact of late‐stage functionalization on OLED characteristics. The present study serves as a proof‐of‐concept for a diversity‐orientated synthesis in the development of MR materials.

Recent advances in materials development for organic light‐emitting diodes (OLEDs) have been driven by an emerging design concept known as multiple‐resonance (MR), which provides the benefits of high efficiency and color purity required for commercial OLED displays. Borylation reaction constructing MR frameworks is a key step for developing new π‐conjugated systems, while this reaction includes the limitation of selectivity, making it challenging to control reactions in elaborate molecular structures. Although a wide variety of MR compounds have been prepared through carefully planned synthetic schemes based on retrosynthetic analysis, these tasks typically require significant effort for each individual target. Herein, we demonstrate a successful late‐stage functionalization strategy that enables structural modifications after the borylation reaction, especially in hardly accessible regions in MR structures via carbon–nitrogen bond cleavage. Our new synthetic method also allows access to new products which were never feasible before. The newly developed material, DABNA‐dimer , proves the impact of late‐stage functionalization on OLED characteristics. The present study serves as a proof‐of‐concept for a diversity‐orientated synthesis in the development of MR materials.

Thermally activated delayed fluorescence (TADF) is a promising mechanism for harvesting triplet excitons in organic light-emitting diodes (OLEDs). The donor–acceptor (D–A) design is the most conventional strategy for developing efficient TADF emitters. A subsequently emerged approach, known as the multiple resonance (MR) effect, also employs electron-donating and electron-withdrawing functional groups. Thus, developing TADF materials has traditionally relied on ingenuity in selecting and combining two functional units. Here, we have realized a TADF molecule by utilizing only a carbazole donor moiety. This molecule is an unusual example in the family of TADF materials and offers better insight into the electronic structures in the excited states for luminescent materials.