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[摘要]：series of cationic water-sol. oligofluorenes up to a chain length of a heptamer. Bromoalkyl-substituted fluorenyl boronic esters as the key intermediates were synthesized by using a modified Miyaura reaction. With an increasing no. of repeat units (trimer to hexamer), the size-specific oligomers have shown red shifts in both the absorption and emission maxima. The emission max. reaches the limit for the hexamer in both water and buffer soln. The quantum yields of the oligomers decreased with increased oligomer size in water. Both fluorescence quenching of the oligomers by 9,10-anthraquinone-2,6-disulfonate and the fluorescence resonance energy transfer expts. with the oligomers as the donor and fluorescein (Fl)- labeled double-stranded DNA (dsDNA-Fl) as the acceptor revealed the chain-length-dependent behavior. The Stern-Volmer quenching const. increased with the mol. size, whereas the highest donor-sensitized Fl emission was obsd. for the hexamer. These size-specific oligomers also served as a model to study the structure-property relationships for cationic polyfluorenes. |
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