Effect of media polarity on the photoisomerisation of substituted stilbene, azobenzene and imine chromophores
作者:N. R. King、Eric A. Whale、Fred J. Davis、Andrew Gilbert、Geoffrey R. Mitchell
DOI:10.1039/a607980f
日期:——
The influence of substituents and media polarity on the
photoinducedE→Z geometrical isomerisation of the
stilbene, azobenzene and N-benzylideneaniline chromophores has
been compared and assessed. The efficiency of the process in all three
systems is markedly dependent on the presence and characteristics of
electron-donor and electron-acceptor substituents at the 4- and
4′-positions. The results are discussed in terms of relaxation of
the E-excited singlet state. In the absence of a nitro
substituent, relaxation to the S
1
orthogonal state competes
effectively with non-productive intramolecular electron transfer; in the
presence of a nitro substituent, the T
1
orthogonal state is
formed from inter-system crossing. For systems with a 4-nitro and a
4′-electron-donor substituent, access to the triplet state is
inhibited by polar solvents promoting formation of the inactive
charge-transfer state from the S
1
state, and no isomerisation
is observed. Similar effects are observed in both solution and polymer
films. Such variations in behaviour have important implications for the
utilisation of the chromophores in nonlinear optical phenomena including
photorefractivity.
我们比较并评估了取代基和介质极性对二苯乙烯、偶氮苯和 N-亚苄基苯胺发色团的光诱导 E→Z 几何异构化的影响。在所有这三个系统中,该过程的效率明显取决于 4-和 4′-位置上电子供体和电子受体取代基的存在和特性。我们从 E 激发单态的弛豫角度对结果进行了讨论。在没有硝基取代基的情况下,向 S 1 正交态的弛豫与非生产性的分子内电子转移有效竞争;在有硝基取代基的情况下,T 1 正交态是由体系间的交叉形成的。对于具有 4-硝基和 4′-电子供体取代基的体系,极性溶剂会抑制三重态的进入,从而促进从 S 1 态形成非活性电荷转移态,并且不会观察到异构化现象。在溶液和聚合物薄膜中也观察到类似的效应。这种行为变化对利用发色团产生非线性光学现象(包括光折射)具有重要意义。