Pyrazinacenes consist of rectilinearly fused 1,4-pyrazine units and can be considered as analogues of the well-studied acene family of compounds with the apical CH units replaced with nitrogen atoms. Herein we discuss the family of pyrazinacene compounds that have been developed recently paying particular attention to their photophysical properties. We show that REDOX properties are dependent on the number of fused rings in the respective pyrazinacenes, and that in their reduced forms, pyrazinacenes are typically highly fluorescent species with solution fluorescence quantum yields typically above 50%, even in extended or deprotonated systems where emission in the near infra-red (NIR) region can be elicited.

Materials with a negative coefficient of thermal expansion (CTE) have been actively studied for compositing with materials with a high CTE to control the CTE. Negative thermal expansion in Zr₂SP₂O₁₂ operates via two main unique mechanisms: phase transition (373-453 K) and framework-type (303-373 K and 453-773 K). Zr₂SP₂O₁₂ is a promising material in this research field because of its relatively low CTE over a wide temperature range. This study describes the mechanism of shrinkage of Zr₂SP₂O₁₂ and introduces control of the CTE by elemental substitution of the Zr sites.

Metal halide perovskite nanocrystals (MHP NCs) show promise as next-generation optical and electronic materials. Surface passivation of MHP NCs to improve polar solvent stability is essential for exploiting their optoelectronic properties. Our group sought to develop novel surface modification methods to improve the chemical and dispersion stabilities of MHP NCs. This short review summarizes our recent reports on the synthesis and optical properties of lead-based perovskite CsPbBr₃ NCs passivated with a cationic oligomeric (gemini, 12-n-12;trimeric, 12-n-12-n-12) ligand. Dynamic light scattering experiments revealed excellent dispersion properties following surface passivation using 12-n-12 ligands with longer spacer groups more than hexylmethylene; other ligands allowed aggregation and precipitation of nanoparticles. Fluorescence spectroscopy showed that CsPbBr₃ NCs passivated with 12-n-12 had fluorescence efficiency comparable to that of didodecyldimethylammonium bromide (DDAB), and that they exhibited water stability. We also elucidated the surface chemistry of CsPbBr₃ NCs passivated with the oligomeric ligands using hard X-ray photoemission spectroscopy (HAXPES).

Hybrid materials offer the potential of coupling the electronic properties of covalent organic molecules and ionic inorganic solids. In the family of hybrid halide perovskites, the diversity of organic molecules has not been observed in three-dimensional (3D) structures due to the small size of the cuboctahedral cage, whereas two-dimensional (2D) derivatives can hold aliphatic and aromatic molecules of a wide range of sizes between the inorganic sheets. Expanded 3D perovskite analogs are emerging materials that mitigate the limitation on the molecular variety in the 3D perovskite, where a single metal-halide octahedron in the perovskite is replaced by a dimer of edge-sharing octahedra. Unlike 3D perovskites, the expanded analogs can hold large molecular dications while maintaining a dispersed inorganic band structure. Flexible choices about organic cations allow us to tune the energy levels of molecular orbitals relative to the inorganic valence and conduction bands. The interplay between active molecular orbitals and inorganic bands affords intriguing optoelectronic properties.