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|Title:||Fluorescent Boron Complexes of 25-Oxasmaragdyrins Containing Axial Silyloxy Groups|
|Publisher:||WILEY-V C H VERLAG GMBH|
|Citation:||EUROPEAN JOURNAL OF INORGANIC CHEMISTRY(29)4810-4818|
|Abstract:||A series of fluorescent B-III complexes of meso-triaryl-substituted 25-oxasmaragdyrins containing axial silyloxy groups were prepared in 80-85% yields by treating B(OH)(2) complexes of meso-triaryl 25-oxasmaragdyrins with different alkyl/aryl chlorosilanes in toluene in the presence of base at reflux temperature followed by simple column chromatographic purification. The eight axially silyloxy-substituted B-III complexes of smaragdyrins were freely soluble in common organic solvents and were characterized by HRMS, 1D and 2D NMR, absorption, fluorescence and electrochemical studies, as well as by X-ray crystallography in the case of one of the complexes. The crystal structure revealed that the smaragdyrin macrocycle is almost planar and that the -OSiMe3 groups on B-III are oriented in the up and down directions relative to the macrocycle. The absorption studies indicated that the axially silyloxy-substituted B-III smaragdyrins are strongly absorbing in the 710-440 nm region with absorption coefficients higher than those of B(OH)(2)-smaragdyrin complexes. The silylation of -OH groups at the B-III centre in the B-III smaragdyrin complex results in five- to sixfold enhancements in the fluorescence quantum yields and in longer singlet state lifetimes. Thus, the axial silyloxy B-III complexes are strongly fluorescent with quantum yields in the 0.65-0.78 range and singlet state lifetimes in the 4.3-4.9 ns range. The complexes are highly stable under redox conditions and each exhibit two reversible oxidations and one reversible reduction.|
|Appears in Collections:||Article|
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