萘和丹酰基修饰的扇形树枝状分子聚集体的能量转移行为

分别对1-3代聚(酰胺-胺)(PAMAM)结构的dendron分子的外端基和focal point进行了修饰,得到了外端基为萘(给体)色团、焦点(focal point)为丹酰(受体)色团的树枝状化合物Dan-ABπ-Nap(n=2,4,8).利用荧光光谱测定了不同浓度下所得一系列树枝状分子在水中的荧光强度,并计算了它...

ENERGY TRANSFER PROPERTY OF THE AGGREGATES FROM NAPHTHYL AND DANSYL MODIFIED POLY(AMIDOAMINE) DENDRONS

The aggregation behavior of the amphiphilic poly(amidoamine)(PAMAM) dendrons(ABn-Nap,Dan-ABn and Dan-ABn-Nap,n denotes the generation of the dendrons,Dan = Dansyl,Nap = Naphthyl) in water was explored and their energy transfer property was studied by using UV-Vis,fluorescence spectroscopy and transmission electron microscopy(TEM).It was found that the modified dendritic molecules aggregated to irregular sphere-like assemblies with the size range of 150 ～ 650 nm.The critical aggregation concentration(CAC) values of ABn-Nap and Dan-ABn-Nap decreased with the generation of dendron increasing,which indicated the enhanced aggregation ability of them.Specially,Dan-AB4 displayed the lowest CAC value,indicating the dendron possessed an appropriate hydrophilic-hydrophobic balance that was a key factor for the aggregation.Notably,the efficient energy transfer occurred from the peripheral naphthyl groups to the focal dansyl unit in the aggregates.While Dan-ABn-Nap aggregates were excited at 282 nm,the fluorescence of naphthyl groups was quenched greatly,instead,strong fluorescence(400 ～ 650 nm) of dansyl groups appeared.The energy transfer efficiencies of different generation dendrons at different concentrations in water were calculated by using Frster theory.Energy transfer occurred with low efficiency when the concentration of dendrons was lower than CAC,for example,the energy transfer efficiency of Dan-AB8-Nap was only 5.7% at the concentration of 1.0 × 10-7 mol/L.However,when the concentration was above CAC(1.0 × 10-4 mol/ L),the energy transfer efficiency improved greatly(77.1%).Interestingly,the energy transfer efficiency of the aggregates in water was higher than that in organic solution at the same concentration.These results can be attributed to the more ordered stacking of the chromophores,closer distance between chromophores and both intermolecular and intramolecular energy transfer in the aggregates.