A 1,3-diazasilabicyclo[1.1.0]butane (1) is synthesized as thermally stable crystals by using the cycloaddition reaction of an isolable dialkylsilylene with aziadamantane. The bridge N−N bond length of 1 (1.70 Å) is the longest among those of known N−N singly-bonded compounds, including side-on bridged transition-metal dinitrogen complexes. The compound 1 is intact in air but moisture sensitive. No reaction occurs with hydrogen, even under pressure at 0.5 MPa. Irradiation of 1 with light gives an isomer quantitatively by N−N and adamantyl C−C bond cleavage. The origin of the remarkable N−N bond elongation is ascribed to significant interaction between a Si−C σ* and Ν−Ν π and σ orbitals as determined by DFT calculations of model compounds.

A 1,3-diazasilabicyclo[1.1.0]butane (1) is synthesized as thermally stable crystals by using the cycloaddition reaction of an isolable dialkylsilylene with aziadamantane. The bridge N−N bond length of 1 (1.70 Å) is the longest among those of known N−N singly-bonded compounds, including side-on bridged transition-metal dinitrogen complexes. The compound 1 is intact in air but moisture sensitive. No reaction occurs with hydrogen, even under pressure at 0.5 MPa. Irradiation of 1 with light gives an isomer quantitatively by N−N and adamantyl C−C bond cleavage. The origin of the remarkable N−N bond elongation is ascribed to significant interaction between a Si−C σ* and Ν−Ν π and σ orbitals as determined by DFT calculations of model compounds.

A 2,6-distyryl-substituted boradiazaindacene (BODIPY) dye and a new series of 2,6-p-dimethylaminostyrene isomers containing both α- and β-position styryl substituents were synthesized by reacting styrene and p-dimethylaminostyrene with an electron-rich diiodo-BODIPY. The dyes were characterized by X-ray crystallography and NMR spectroscopy and their photophysical properties were investigated and analyzed by carrying out a series of theoretical calculations. The absorption spectra contain markedly redshifted absorbance bands due to conjugation between the styryl moieties and the main BODIPY fluorophore. Very low fluorescence quantum yields and significant Stokes shifts are observed for 2,6-distyryl-substituted BODIPYs, relative to analogous 3,5-distyryl- and 1,7-distyryl-substituted BODIPYs. Although the fluorescence of the compound with β-position styryl substituents on both pyrrole moieties and one with both β- and α-position substituents was completely quenched, the compound with only α-position substituents exhibits weak emission in polar solvents, but moderately intense emission with a quantum yield of 0.49 in hexane. Protonation studies have demonstrated that these 2,6-p-dimethylaminostyrene isomers can be used as sensors for changes in pH. Theoretical calculations provide strong evidence that styryl rotation and the formation of non-emissive charge-separated S₁ states play a pivotal role in shaping the fluorescence properties of these dyes. Molecular orbital theory is used as a conceptual framework to describe the electronic structures of the BODIPY core and an analysis of the angular nodal patterns provides a reasonable explanation for why the introduction of substituents at different positions on the BODIPY core has markedly differing effects.

Boron dipyrromethenes (BODIPYs) with bulky triphenylsilylphenyl(ethynyl) and triphenylsilylphenyl substituents on pyrrole sites were prepared via Hagihara–Sonogashira and Suzuki–Miyaura cross-coupling with ethynyl-terminated tetraphenylsilane and boronic acid-terminated tetraphenylsilane. The chromophores are designed to prevent intermolecular π–π stacking interaction and enhance fluorescence in the solid state. Single crystals of 1 a and 2 b for X-ray structural analysis were obtained, and weak π–π stacking interactions of the neighboring BODIPY molecules were observed. Spectroscopic properties of all of the dyes in various solvents and in films were investigated. Triphenylsilylphenyl-substituted BODIPYs generally show more pronounced increases in solid-state emission than triphenylsilylphenyl(ethynyl)-substituted BODIPYs. Although the simple BODIPYs do not exhibit any fluorescence in the solid state (Φ=0), arylsilyl-substituted BODIPYs exhibit weak to moderate solid-state fluorescence with quantum yields of 0.03, 0.07, 0.10, and 0.25. The structure–property relationships were analyzed on the basis of X-ray crystallography, optical spectroscopy, cyclic voltammetry, and theoretical calculations.