| Abstract
| - Seven fluorescent boradiazaindacene-based compounds with one or two phenyl, ethenylphenyl, andethynylphenyl substituents at the 3- (or 3,5-) position(s) were synthesized via palladium-catalyzed couplingreactions with the appropriate 3,5-dichloroBODIPY derivative. The effect of the various substituents at the3- (or 3,5-) position(s) on the spectroscopic and photophysical properties were studied as a function of solventby means of UV/vis absorption, steady-state, and time-resolved fluorometry, and theoretical modeling. Theemission maxima of the symmetrically 3,5-disubstituted dyes are shifted to longer wavelengths (by 30 to 60nm) relative to the related asymmetrically 3,5-disubstituted ones. Introduction of styryl substituents causesthe largest red shift in both the absorption and emission spectra. BODIPY derivatives with ethynylaryl groupsalso shift the spectral maxima to longer wavelengths compared to aryl-substituted ones but to a lesser degreethan the styryl compounds. The quantum-chemical calculations confirm these trends and provide a rationalefor the spectral shifts induced by substitution. The fluorescence quantum yields of the ethenylaryl andethynylaryl analogs are significantly higher that those of the aryl-substituted dyes. The 3,5-diethynylaryl dyehas the highest fluorescence quantum yield (∼1.0) and longest lifetime (around 6.5 ns) among the BODIPYdyes studied. The differences in the photophysical properties of the dyes are also reflected in theirelectrochemical properties where the symmetrically 3,5-disubstituted dyes display much lower oxidationpotentials when compared to their asymmetric counterparts.
|
