Photochemical and photophysical properties of a poly(propylene amine) dendrimer functionalised with E-stilbene units
作者:Veronica Vicinelli、Paola Ceroni、Mauro Maestri、Mariachiara Lazzari、Vincenzo Balzani、Sang-Kyu Lee、Jeroen van Heyst、Fritz Vögtle
DOI:10.1039/b404463k
日期:——
A second generation poly(propylene amine) dendrimer (2) functionalised at the periphery with eight E-stilbene and eight 4-tert-butylbenzenesulfonyl units has been prepared. The absorption spectrum, fluorescence spectrum and decay, E
⇆
Z photoisomerization, and photocyclization of the Z-isomer of the stilbene units have been investigated in air equilibrated acetonitrile solutions. For comparison purposes, a reference compound of the peripheral dendrimer units, namely 4-tert-butyl-N-propyl-N-(4-styryl-benzyl)-benzenesulfonamide (1), has also been studied. The quantum yield of the E→Z photoisomerization reaction (0.30) and the fluorescence quantum yield of the E isomer (0.014) are substantially smaller for the units appended to the dendrimer compared to those of the reference compound 1
(0.50 and 0.046, respectively). The presence of a red tail and the biexponential decay of the emission band of the dendrimer indicate formation of excimers between the stilbene units appended at the poly(propylene amine) dendritic structure. Under the experimental conditions used (λexc
= 313 nm), a Z/E photostationary state (around 9 ∶ 1 for both reference compound 1 and dendrimer 2) is reached in the time scale of minutes. On continuing irradiation, other photoreactions take place in the time scale of hours: the stilbene moiety of compound 1 undergoes photocyclization to phenanthrene (quantum yield 0.015), whereas in dendrimer 2 photocyclization to phenanthrene is accompanied by other processes, including a photoreaction involving the internal amine groups.
已合成一种第二代聚(丙烯胺)树状聚合物(2),其外围功能化有八个E-苯乙烯和八个4-叔丁基苯磺酰基单位。已在空气平衡的乙腈溶液中研究了其吸收光谱、荧光光谱及衰减情况、E⇆Z光异构化以及Z-异构体的光环化。为比较 purposes,作为外围树状聚合物单位的参考化合物,即4-叔丁基-N-丙基-N-(4-苯乙烯基-苄基)-苯磺酰胺(1),也进行了研究。与参考化合物1(分别为0.50和0.046)相比,树状聚合物上附加单位的E→Z光异构化反应的量子产率(0.30)和E异构体的荧光量子产率(0.014)显著较小。树状聚合物发射带的红尾和双指数衰减表明在聚(丙烯胺)树状结构中附加的苯乙烯单位之间形成了激基体。在所用的实验条件下(λexc = 313 nm),达到一个Z/E光静态状态(参考化合物1和树状聚合物2均约为9∶1),时间尺度为几分钟。在持续照射的情况下,其他光反应发生在小时级别的时间尺度内:化合物1的苯乙烯基团经历光环化生成菲(量子产率为0.015),而在树状聚合物2中,光环化生成菲伴随着其他过程,包括涉及内胺基团的光反应。