Facile strategy for obtaining luminescent polymorphs based on the chirality of a boron-fused azomethine complex

A chloro-substituted boron-fused azomethine complex (BAmCl) having a stereogenic boron center was synthesized for obtaining a luminescent chiral crystal. We succeeded in isolating the (R)- and (S)-enantiomers of BAmCl and preparing the homochiral polymorphic crystal, while we obtained the racemic crystal with rac-BAmCl. Single crystal X-ray diffraction analyses suggest that a variety of intermolecular interaction patterns and intrinsic flexibility of the molecular framework should play a significant role in stabilizing the homochiral crystal. We found the difference in molecular arrangements between the racemic and the homochiral crystals, and we observed distinctly different emission colors. In particular, we observed heat-initiated homogeneous racemization without the need for a solvent or catalyst in the molten state of the homochiral crystal (R)-BAmCl. Our results mean that chiral resolution of a flexible fused-skeleton having a stereogenic boron center can be a platform for creating luminescent polymorphic materials

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MAGIC and H.E.S.S. detect VHE gamma rays from the blazar OT081 for the first time: a deep multiwavelength study

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Synthesis of fully-fused bisboron azomethine complexes and their conjugated polymers with solid-state near-infrared emission

We describe herein a robust π-conjugated molecules with solid-state emission in the near-infrared (NIR) region (ΦF = 0.03–0.06). Initially, the diastereomers of bisboron azomethine complexes having phenyl groups in the same and opposite directions to the π-plane were synthesized. These diastereomers showed emission properties with larger red-shifts (>200 nm) and 10 times larger emission efficiencies than those of the mononuclear complex. Theoretical calculation data indicate that superior optical properties of the bisboron complexes should be attributable to efficient expansion of the π-conjugated system. In addition, the bisboron compounds and their conjugated polymers exhibited intense NIR emissions even in the solid state

Selective modulation of energy levels of frontier orbitals in solid-state luminescent boron-fused azomethine polymers with orthogonal orientations to the main chains

The development of polymers with film luminescence and property tuning is still a relevant topic due to concentration quenching which most of the organic luminophores suffer from. Based on boron-fused azomethine (BAm) complexes which can show aggregation-induced emission (AIE) and crystallization-induced emission (CIE), we previously obtained solid-state luminescent polymers. In this study, we synthesized π-conjugated polymers involving BAms orthogonally oriented to the main chains. In particular, the synthesized polymers have quite different properties from parallell-oriented BAm-consisting π-conjugated polymers that have been previously reported. The synthesized polymers can show intense luminescence in solutions and films. Moreover, we found that the energy levels of one of the frontier molecular orbitals (FMOs) can be selectively perturbed depending on the ligand structure. Furthermore, by selecting condensed reagents in the azomethine bond formation reaction, the monomer structure followed by the perturbed FMO can be determined. Finally, we observed that the synthesized polymers exhibit steady emission in both solutions and films in the near-infrared (NIR) region (λPL = 686 nm, ΦPL = 4% in solution, λPL = 709 nm, and ΦPL = 3% in film). Computer calculations support these experimental data. In this study, a new series of solid-state luminescent π-conjugated polymers with tunable energy levels is demonstrated