We have investigated the absorption spectra, the fluorescence spectra and decay and the electrochemical redox processes of five dendrimers Gn (n = 1 to 5) that contain 2n+1 - 2 (i.e., 62 for G5) tertiary amino groups in the interior and 2n+1 (i.e., 64 for G5) 1,2-dimethoxybenzene (DMB) units in the periphery. In dichloromethane solution the absorption spectrum of the dendrimers is quite similar to that of 3,4-dimethoxy-N-propylbenzene-1- sulfonamide, a model compound of the peripheral DMB units. The fluorescence band of the DMB unit (λmax = 319 nm, τ = 0.95 ns, Φ = 0.08 for the model compound), however, is much weaker in the dendrimers, which also display a broad emission tail above 450 nm (τ from 2 to 7 ns, depending on dendrimer generation), assigned to exciplex formation between the peripheral dimethoxybenzene groups and the inner tertiary amino groups. Upon addition of trifluoroacetic acid, which causes protonation of the inner amino groups of the dendrimers, the intensity of exciplex emission decreases and the intensity of the 319 nm band of the DMB units increases, reaches a maximum, and then decreases with increasing protonation of the dendrimer interior, presumably because of excimer formation between peripheral DMB units. Electrochemical investigations have shown that in acetonitrile the dendrimers exhibit a reversible, multielectron oxidation wave at about +1.7 V vs SCE, assigned to the peripheral DMB units and broad anodic peaks in the region +0.8/+1.5 V, assigned to oxidation of the inner tertiary amino groups.
我们研究了包含2
n+1 - 2(即,对于
G5为62)个第三级胺基团和2
n+1(即,对于
G5为64)个1,2-二
甲氧基苯(
DMB)单元的五种树枝状分子
Gn(
n = 1至5)的吸收光谱、荧光光谱和衰减以及电
化学氧化还原过程。在
二氯甲烷溶液中,树枝状分子的吸收光谱与3,4-二甲氧基-N-丙基苯磺酰胺的外围
DMB单元的模型化合物相似。然而,
DMB单元的荧光带(λ
max = 319 nm,τ = 0.95 ns,Φ = 0.08,对于模型化合物)在树枝状分子中要弱得多,树枝状分子还显示出在450 nm以上的宽发射尾巴(τ从2到7 ns,取决于树枝状分子的代数),被归因于外围二
甲氧基苯基团和内部第三级胺基团之间的激基复合物形成。加入
三氟乙酸后,导致树枝状分子内部
氨基团质子化,激基复合物发射强度减小,
DMB单元的319 nm带的强度增加,达到最大值,然后随着树枝状分子内部质子化的增加而减小,可能是由于外围
DMB单元之间的激聚物形成。电
化学研究表明,在
乙腈中,树枝状分子在约+1.7 V
vs SCE处表现出可逆的多电子氧化波,被归因于外围
DMB单元,并且在+0.8/+1.5 V区域显示出宽广的阳极峰,被归因于内部第三级胺基团的氧化。