Abstract
Vinylene-bridged cyclic boron–difluoride complex of dipyrrin (BODIPY) trimers were successfully prepared from expanded dimethyl-vinylene bridged hexaphyrin(2.1.2.1.2.1) Me-Hex that has the structure of alternate dipyrrins and vinylene bridges. The hexaphyrin(2.1.2.1.2.1) Me-Hex can coordinate with boron ions to afford five kinds of cyclic BODIPYs given by step-by-step boron complexations. Crystal structures of all cyclic BODIPYs except for 3BF2-Me-Hex(b) formed non-planar structures. The theoretical calculation predicted that mono-/bis-boron cyclic BODIPYs show the intramolecular charge transfer (ICT) characteristics, whereas tri-boron cyclic BODIPYs have no ICT characteristics. Reflecting these electronic properties, tri-boron cyclic BODIPYs exhibit weak fluorescence in the red region, but mono-/bis-boron cyclic BODIPYs exhibit no emission. Vinylene bridged cyclic dipyrrin trimer Me-Hex is the novel porphyrinoid ligand allowed to control the boron coordination under different reaction conditions to form various boron complexes.
Highlights
A boron–difluoride complex of dipyrrin (BODIPY) is an outstanding fluorescent dye with high fluorescence quantum yield and high chemical robustness [1,2,3,4]
Shinokubo and co-workers developed the synthesis of planar BODIPY dimer and trimer (c-BODIPY-1), linked through butadiyne by sila-Glaser coupling reaction (Figure 1) [9]
The configuration of Ph-Hex is changed to the cis-vinylene-bridged figure-of-eight structure with the aromatic property by insertion of copper ions [18]. These results indicate that the expanded porphyrins having vinylene-bridges are curious ligands to make metal complexes accompanied by changes in molecular configurations and electronic properties
Summary
A boron–difluoride complex of dipyrrin (BODIPY) is an outstanding fluorescent dye with high fluorescence quantum yield and high chemical robustness [1,2,3,4]. Shinokubo and co-workers developed the synthesis of planar BODIPY dimer and trimer (c-BODIPY-1), linked through butadiyne by sila-Glaser coupling reaction (Figure 1) [9]. These cyclic BODIPYs are stable anti-aromatic compounds with NIR absorbing properties. Nabeshima and co-workers reported a series of cyclic BODIPY oligomers linked through metaand para-phenylenes (c-BODIPY-2 and c-BODIPY-3) (Figure 1) [11,12,13,14,15]. Their results show that the expanded porphyrins containing π-conjugated bridging units could be excellent precursors for the preparation of cyclic BODIPY oligomers. The relationship between the number of coordinated boron atoms and molecular configuration/optical properties of expanded porphyrins is still unclear
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