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The crystal-packing structures of seven derivatives of diaroylmethanatoboron difluoride ( 1 a- gBF2) are characterized by no overlap of the π-conjugated main units of two adjacent molecules (type I), overlap of the benzene ring π-orbitals of two adjacent molecules (type II), and overlap of the benzene and dihydrodioxaborinine rings π-orbitals of adjacent molecules (type III). The crystal-packing structures govern the fluorescence (FL) properties in the crystalline states. The FL domain that is present in type I crystals, in which intermolecular orbital interactions are absent, leads to excited monomer-like FL properties. In the case of the type II crystals, the presence of intermolecular overlap of the benzene rings π-orbitals generates new FL domains, referred to as 'excited multimers', which possess allowed S0-S1 electronic transitions and, as a result, similar FL lifetimes at longer wavelengths than the FL of the type I crystals. Finally, intermolecular overlap of the benzene and dihydrodioxaborinine ring π-orbitals in the type III crystals leads to 'excited multimer' domains with forbidden S0-S1 electronic transitions and longer FL lifetimes at similar wavelengths as that in type I crystals. [ABSTRACT FROM AUTHOR]

The Way of Tea in the world of molecules: Sakai City, where the authors’ Osaka Prefecture University is located, is internationally famous for the Way of Tea. This cover picture displays the traditional Japanese tea ceremony using powdered green tea served with rice dumplings and sugar candies, which is specially made from molecular models of boron complexes and their fluorescent crystals, respectively. The crystal packing structure of them controls its fluorescence domain, the excited monomer, excimer, and “excited multimer”, which show a different fluorescence wavelength, lifetime, and quantum yield. For more information see the Full Paper by H. Ikeda et al. on page 18128 ff. [ABSTRACT FROM AUTHOR]

Abstract: Metal-ion complexation of 7-benzylimidazo[1,2-a]pyrazin-3(7H)-one derivative (2) with Li+, Mg2+, Ca2+, Ba2+, Sc3+, and La3+ in acetonitrile resulted in successive modulations of its UV/vis absorption and fluorescence spectroscopic properties. This result indicates that 2 can be used as a colorimetric and fluorometric sensor of the Lewis acidity of a metal ion in aprotic solutions. The hypothesis that the metal-ion complex has a O10(imidazopyrazinone)–metal ion bond was supported by X-ray crystallographic analysis and quantum chemical calculations for a Li+ complex of 7-methylimidazo[1,2-a]pyrazin-3(7H)-one derivative (1). [Copyright &y& Elsevier]