Competition between Photoisomerization and Photocyclization of the Cis Isomers of n-Styrylnaphthalenes and -Phenanthrenes
Competition between Photoisomerization and Photocyclization of the Cis Isomers of n-Styrylnaphthalenes and -Phenanthrenes
复制标题
DOI：
10.1021/jp904017e
复制
发表时间：
2009-12-31
影响因子：
2.9
通讯作者：
Spalletti, A.
中科院分区：
文献类型：
--
作者：
Mazzucato, U.;Spalletti, A.
用分光光度和层析技术研究了N-苯基萘(n=1和2)，n-苯基菲(n=1，2，3，4和9)的顺式(Z)异构体及其两个相关化合物3-苯基黄烯和3-苯基苯并[c]菲的异构化和环化光反应。在室温下测量了这两种光反应在充气和脱气非极性溶剂中的量子产率，并与文献报道的一些分子和其他相关化合物的量子产率进行了比较。高效液相色谱技术和分光光度技术的结合使用使光反应混合物的组成更容易分离，从而简化了异构化/环化竞争的研究，并简化了二氢菲类中间体的UV-Vis吸收光谱和热衰减动力学的测量。基态构象平衡和位置异构性(n值)显著影响一种或另一种竞争性光反应的流行。氧也扮演着重要的角色：实际上，它不影响Z->；E过程的量子产率，但对最终氧化产物的形成有巨大影响，即使存在微量空气也可以进行。在三种情况下，检测到不可忽略的无色副产物的形成。它被指定为正常的光环化中间体(4a，4b-二氢菲类型)的异构体，由一个或两个氢原子(S)移动到环的其他位置而形成。对可能构象势能的平行从头计算有助于解释结构对竞争性光反应弛豫路径的影响。计算的基态试剂/产物能差与中间体的光环化产率和热稳定性之间也有一定的相关性。
The isomerization and cyclization photoreactions of the cis (Z) isomers of n-styrylnaphthalenes (n = 1 and 2), n-styrylphenanthrenes (n = 1, 2, 3, 4, and 9), and two related compounds, 3-styrylchrysene and 3-styrylbenzo[c]phenanthrene, were investigated by spectrophotometric and chromatographic techniques. The quantum yields of the two photoreactions were measured in aerated and deaerated nonpolar solvent at room temperature and compared with those reported in the literature for some of the molecules investigated and other related compounds. The combined use of high-performance liquid chromatographic and spectrophotometric techniques made easier the separation of the components of the photoreaction mixtures thus simplifying the study of the isomerization/cyclization competition and the measurement of the UV-vis absorption spectra and the thermal decay kinetics of the dihydrophenanthrene-type intermediates. The conformational equilibria in the ground state and the positional isomerism (n values) notably affect the prevalence of one or the other competitive photoreaction. Oxygen also plays an important role: practically it does not affect the quantum yield of the Z -> E process but has a drastic effect on the formation of the final oxidation product which call proceed even in the presence of traces of air. In three cases, non-negligible formation of a side colorless product was detected. It was assigned to an isomer of the normal photocyclization intermediate (4a,4b-dihydrophenanthrene-type), formed by shift of one or both hydrogen atom(s) to other positions of the rings. Parallel ab initio calculations of the potential energy of the possible conformers helped to explain the Structure effects on the competitive photoreactive relaxation pathways. Some correlations between the Computed reagent/product energy difference in the ground state and the photocyclization yield and thermal stability of the intermediates were also verified.