Takumi Matsuo

Organic single‐crystal lasers require materials that unite strong solid‐state luminescence, controlled crystallization, and well‐defined optical resonator structures. However, π–π stacking, polymorphism, and aggregation‐induced quenching frequently impede the reliable molecular design of such systems. Here, we report β‐dicyanostilbene (βDCS)‐based luminogens engineered to address these challenges through the introduction of tert ‐butyl groups and fluorine substituents, which synergistically enhance solubility, suppress π–π interactions, and generate a twisted molecular geometry. Solution‐phase crystallization at room temperature yielded two distinct polymorphs, each possessing markedly different packing arrangements yet similarly high luminescence efficiencies. Both polymorphs exhibited monomer‐like emission in the solid state and demonstrated clear laser oscillation. Structural analysis and Hirshfeld surface mapping confirmed the absence of π–π stacking in either crystal, while time‐dependent density functional theory (TD‐DFT) calculations indicated that the emission originates primarily from π–π* transitions along the molecular long axis. Notably, the ability of both polymorphs to lase—despite their distinct crystal architectures—challenges the conventional assumption that polymorphism degrades laser performance. These findings establish bulky‐substituent introduction and controlled molecular twisting as effective design strategies for achieving polymorph control, preserving luminescence properties, and enabling laser oscillation in βDCS‐based single‐crystal materials.

π‐Conjugated molecules with highly π‐extended structures are important for optoelectronic applications. Naphthobischalcogendiazole backbones are recently developed electron‐accepting π‐extended structures. Herein, we report the discovery of a whitish luminescence based on the appearance of multiple PL bands for boronate pinacol ester (Bpin)‐appended naphtho[1,2‐c:5,6‐c′]bis[1,2,5]oxadiazole ( NOz ) crystal. The appearance of these multiple PL bands was interpreted by the close packing of PB2‐NOz , which was likely assisted by intermolecular short contacts involving the Bpin units. This discovery suggests that the strong intermolecular interaction by Bpin can be exploited for the crystal engineering toward versatile optoelectronic functions, rather than being used solely as conventional building blocks in coupling reactions.

Single-crystals composed of organic π-conjugated molecules with high solid-state luminescence are promising candidates for laser media.

Abstract Highly solid‐state emissive molecular crystals have attracted attention as gain media for organic lasers. There is a need to develop solid‐state luminescent molecules with excellent solubility and thermal stability through chemical design approaches despite the structural and functional diversity of organic molecular materials toward such media. Here, we report the synthesis and properties of the t‐butyl‐ and pyridyl or phenyl‐appended cyano‐β‐substituted distyrylbenzenes (CDSBs). A solution process at room temperature could prepare each crystal of these molecules modified with pyridyl/phenyl. The crystal structure analysis results suggest that the difference in the pyridyl/phenyl group affects the crystal system. Solid‐state emissions were similar due to the molecular structural differences affecting only the crystal structure. The emission spectrum of the crystal exhibited amplified spontaneous emission (ASE) properties with the formation of population inversion. However, the pyridyl–pyridyl interactions contributed to the thermal stability of the crystal, which was stable even under high‐energy density laser irradiation. Therefore, molecular modification with the pyridyl group offers a new strategy for controlling crystal structures and rigid frameworks.

Luminescent organic single crystals are attractive as components of miniaturized photonic integrated circuits such as optical waveguides, lasers, and optical resonators. Various functions have been discovered by designing chemical or...

Abstract Naphtho[1,2‐c:5,6‐c]bis[1,2,5]chalcogendiazole is an important building block for organic devices due to its highly electron‐accepting properties. However, despite being an effective unit of low band gap organic semiconductors, fewer studies have been conducted on analyzing such units to understand their crystal structure. Here the crystal structure analysis of naphtho[1,2‐c:5,6‐c]bis[1,2,5]thiadiazole, naphtho[1,2‐c:5,6‐c]bis[1,2,5]oxadiazole is reported, and these brominated motifs. Crystal structures of naphtho[1,2‐c:5,6‐c]bis[1,2,5]thiadiazoles and its brominated compound show that the molecules form coplanar structures through N···S contacts, resulting in parallel face‐to‐face packing and π‐π stacking. Double N···S contacts are found as a priority in such compounds. On the other hand, naphtho[1,2‐c:5,6‐c]bis[1,2,5]oxadiazoles gave N···H─C networks with π‐π stacking. These differences will probably induce the difference in the crystal structure of the naphtho[1,2‐c:5,6‐c]bis[1,2,5]chalcogendiazole‐based extended π‐systems. Brominated one exhibits polymorphs, which works N···Br contacts or Br···Br contacts based on the interaction of the σ‐hole of bromide. These investigations can be applied to the order‐made synthesis of self‐assembled soft matter and functional molecular crystals.

Abstract Optical waveguides based on elastic molecular crystals are of interest as flexible and compact optical communication materials. Low emission efficiency is often a problem in terms of communication signal strength, and an increase in the loss factor α due to fluorescence reabsorption in the crystal reduces the photon transport efficiency. Here, we report the development and improvement of Förster resonance energy transfer (FRET)-assisted optical waveguides using anthracene-based elastic mixed molecular crystals. 9,10-Dicyanoanthracene was selected as the dopant for solution-grown crystallization of 9,10-dibromoanthracene. 1H NMR measurements of the obtained crystals showed that the acceptor doping to be 1% to 5%. Elastic behavior was observed even when doped with a few percent of the acceptor. The quantum efficiency was 0.016, a dramatic improvement over the previous luminescent elastic mixed molecular crystals (0.004). The α value (92 dB/cm) of this crystal containing 1%-doped 9,10-dicyanoanthracene is much lower than that of the crystal consisting of only 9,10-dibromoanthracene (1258 dB/cm) due to the reduced reabsorption in the FRET system. We have demonstrated a practical approach toward developing improved fluorescent, highly efficient, and flexible optical waveguides by constructing the mixed crystal structure by selecting appropriate acceptor molecules and their low doping ratios.

Benzocarcogendiazole units have been frequently utilized for optoelectronics such as organic solar cells because of their robustness, rigidity, and band-gap tunability based on the strong electron-withdrawing properties. Focusing on the luminescent characteristics, these molecules have been utilized to demonstrate highly sensitive chromisms because of the potential of charge transfer. Here, we demonstrate deep red-emissions in bis(4-tert-butylphenyl)amine-appended benzocarcogendiazole-based donor-acceptor-donor (D-A-D) fluorophores, namely 1 and 2. Because benzocarcogendiazole and bis(4-tert-butylphenyl)amineserve as strong electron acceptor and donor, respectively, strong intramolecular charge transfer (ICT) enables long wavelength of photoluminescence (PL) even in the small molecular weight. Although photoluminescence (PL) in long wavelength tends to exhibit quite low PL quantum efficiency (ΦPL), the values of solutions 1 and 2 are quite high (up to 50 %). According to X-ray crystallographic characterizations and DFT calculations, these high ΦPL values are attributable to the segregated π-planes of benzocarcogendiazole units, which is induced by the bulky substituents of bis(4-tert-butylphenyl)amines.

Abstract Whispering‐gallery‐mode (WGM) resonators composed of organic and/or inorganic materials have been used in highly sensitive sensors, logic gates, and miniaturized lasers because of the total internal reflection of photons. However, most fabrication methods have been limited to bottom‐up self‐assembly; whereas, a facile top‐down process is preferable. Here, a wet‐process fabrication of WGM resonators mixed with 5 µm‐diameter spherical silica‐gels and various π‐conjugated compounds is demonstrated. The materials are fabricated by dip‐coating photoluminescent molecules onto submicron‐scale silica‐gel spheres. The shapes and large specific surface areas of templates are maintained before and after coating, and the coated molecules are uniformly distributed. The hybrid spheres provided WGM photoluminescence spectra based on the total internal reflection of photoluminescence in the sphere. The hybrid spheres are applicable as WGM sensors because of their large specific surface area (>4 × 10² m² g⁻¹). In particular, gas sensing of toluene, which has been used as a standard for environmental contamination, and found that the WGM photoluminescence peaks are shifted by 5 nm is demonstrated. The detection resolution is calculated to be several hundred ppm level. The hybrid spheres can be placed or transferred onto various surfaces without micromanipulation, which suggested a wide range of possible applications.

A methylated flufenamic acid gave two different polymorphs, mechanically deformable α form and fragile γ form. We successfully obtained the “intrinsically brittle” bent γ crystal by vapor-induced phase transition from the bent α crystal.

To realize organic integrated optoelectronic circuits, there is a need for anisotropic optical waveguides at the micro/nanoscale. Anisotropic alignment of one‐dimensional (1D)‐ordered supramolecular structures composed of light‐emissive π‐conjugated molecules in a crystal may meet the requirements of such waveguides. Here, we designed a bipyridyl‐appended acrylonitrile‐based π‐conjugated molecule 1, which produced a 1D supramolecular polymer constructed through non‐covalent bonding between a lone pair in 1 and a σ‐hole in 1,4‐diiodo‐2,3,5,6‐tetrafluorobenzene 2. The 1D copolymer of 1 and 2 is aligned horizontally with the two‐dimensional (2D) crystal surface because of the angle‐controlled supramolecular synthons. As a result of control over the non‐covalent bonding direction, anisotropic photoluminescence and photon transport (optical waveguiding) characteristics are realized by orienting the transition dipole moment horizontally with respect to the 2D surface. Compared with the loss coefficient αL =52dBcm‐1 for the long‐axis direction of the 2D platelet cocrystal, a very large difference of αS =2111dBcm‐1 is present in the crystal short‐axis direction. The anisotropic waveguiding ability, αL/αS, is estimated to be 41, which is more than an order of magnitude greater than previously reported 2D platelet crystal waveguides. This supramolecular synthon provides an approach to designing anisotropic photon transporters and highly regulated optical logic circuits.