Meso-thienyl and furyl rotor effects in BF2-chelated dipyrrin dyes: solution spectroscopic studies and X-ray structural packing analysis of isomer and congener effects

Abstract

Well-defined discrete fluorescent molecular systems with very subtle steric/electronic differences are interesting when considering solid-state packing and solution substituent effects. Herein, we report the synthesis and characterization of four 4,4-difluoro-1,3,5,7-tetramethyl-8-(C4H3 X)-4-bora-3a,4a-diaza-s-indacene complexes (X = O, S). Various NMR spectroscopic experiments were used to assign all relevant atoms (CD2Cl2): 19F, 11B, 1H, 13C, 13C–H undecoupled, 1H–1H COSY, 1H–1H NOESY, 1H–13C HSQC, and 1H–13C HMBC NMR spectroscopy. UV-Vis and fluorescence studies were undertaken for all compounds. Chemical shift differences were found between isomers and congeners; for congeners, aromatic δ differences were attributed to electron-poor character. Also, compounds 1–4 were studied crystallographically. In the solid state, internal dihedral planes and intermolecular packing patterns can be compared.