Pérez-Prieto Julia, Stiriba Salah-Eddine, Boscá Francisco, Lahoz Agustín, Domingo Luis R, Mourabit Fouad, Monti Sandra, Miranda Miguel A
Departamento de Química Orgánica/ICMOL, Universidad de Valencia, Av. Vicent Andrés Estellés s/n, 46100 Burjassot, Valencia.
J Org Chem. 2004 Dec 10;69(25):8618-25. doi: 10.1021/jo048973v.
Laser flash photolysis of a series of bichromophoric compounds 1-12 containing the 2-benzoylthiophene (BT) and phenol (PhOH) or indole (InH) moieties has been used to determine the possible geometrical effects in the intramolecular quenching of triplet excited ketones, resulting in formal hydrogen abstraction. The results are compared with those obtained in the intermolecular process. In both cases, substitution either at the thienyl or the phenyl moiety has a marked influence on the photoreactivity. Time-resolved experiments showed that the rate constants for bimolecular quenching by phenol and indole of 2-benzoylthiophene substituted at the thienyl 5-position were lower than those for BT substituted at the phenyl p-position, which agrees with the higher energy found for the excited triplet state of the latter compounds. However, the rate constant for hydrogen abstraction in the bichromophoric compounds by the pi,pi* triplet state of the derivatives with the spacer linked to the thienyl 5-position are higher than those of their regioisomers. These results indicate a possible geometry-dependence in the intramolecular quenching process. Theoretical DFT studies have been carried out in order to estimate the optimum conformation for hydrogen abstraction in two pairs of phenolic and indolic bichromophoric regioisomers. The energy profile for photoactivation/deactivation of the aromatic ketone and the structures of the triplet states and biradicals involved in the process have been determined. The observed regiodifferentiation in the experimental studies is consistent with a dependence of the rate constant on orbital overlap between the carbonyl oxygen and the X-H bonds.
利用一系列含有2-苯甲酰基噻吩（BT）和苯酚（PhOH）或吲哚（InH）部分的双色团化合物1-12进行激光闪光光解，以确定三重激发酮分子内猝灭中可能的几何效应，从而导致形式上的氢提取。将结果与分子间过程中获得的结果进行比较。在这两种情况下，噻吩基或苯基部分的取代对光反应性都有显著影响。时间分辨实验表明，噻吩基5位取代的2-苯甲酰基噻吩被苯酚和吲哚进行双分子猝灭的速率常数低于苯基对位取代的BT的速率常数，这与后一种化合物激发三重态的较高能量一致。然而，间隔基连接到噻吩基5位的衍生物的π,π*三重态在双色团化合物中进行氢提取的速率常数高于其区域异构体。这些结果表明分子内猝灭过程中可能存在几何依赖性。为了估计两对酚类和吲哚类双色团区域异构体中氢提取的最佳构象，进行了理论DFT研究。确定了芳香酮光活化/失活的能量分布以及该过程中涉及的三重态和双自由基的结构。实验研究中观察到的区域分化与速率常数对羰基氧和X-H键之间轨道重叠的依赖性一致。
