Tanner Christian, Thut Markus, Steinlin Andreas, Manca Carine, Leutwyler Samuel
Departement für Chemie und Biochemie, Universität Bern, Freiestrasse 3, CH-3012 Bern, Switzerland.
J Phys Chem A. 2006 Feb 9;110(5):1758-66. doi: 10.1021/jp056151b.
Excited-state hydrogen-atom transfer (ESHAT) along a hydrogen-bonded solvent wire occurs for the supersonically cooled n = 3 ammonia-wire cluster attached to the scaffold molecule 7-hydroxyquinoline (7HQ) [Tanner, C.; et al. Science 2003, 302, 1736]. Here, we study the analogous three-membered solvent-wire clusters 7HQ.(NH3)n.(H2O)m, n + m = 3, using resonant two-photon ionization (R2PI) and UV-UV hole-burning spectroscopies. Substitution of H2O for NH3 has a dramatic effect on the excited-state H-atom transfer: The threshold for the ESHAT reaction is approximately 200 cm(-1) for 7HQ.(NH3)3, approximately 350 cm(-1) for both isomers of the 7HQ.(NH3)2.H2O cluster, and approximately 600 cm(-1) for 7HQ.NH3.(H2O)2 but increases to approximately 2000 cm(-1) for the pure 7HQ.(H2O)3 water-wire cluster. To understand the effect of the chemical composition of the solvent wire on the H-atom transfer, the reaction profiles of the low-lying electronic excited states of the n = 3 pure and mixed solvent-wire clusters are calculated with the configuration interaction singles (CIS) method. For those solvent wires with an NH3 molecule at the first position, injection of the H atom into the wire can occur by tunneling. However, further H-atom transfer is blocked by a high barrier at the first (and second) H2O molecule along the solvent wire. H-atom transfer along the entire length of the solvent wire, leading to formation of the 7-ketoquinoline (7KQ) tautomer, cannot occur for any of the H2O-containing clusters, in agreement with experimentally observed absence of 7KQ fluorescence.
对于附着在支架分子7-羟基喹啉（7HQ）上的超声速冷却的n = 3氨线簇，会发生沿氢键溶剂线的激发态氢原子转移（ESHAT）[坦纳，C.；等人。《科学》2003年，302卷，1736页]。在此，我们使用共振双光子电离（R2PI）和紫外-紫外空穴烧蚀光谱研究类似的三元溶剂线簇7HQ.(NH3)n.(H2O)m，n + m = 3。用H2O取代NH3对激发态氢原子转移有显著影响：对于7HQ.(NH3)3，ESHAT反应的阈值约为200厘米-1；对于7HQ.(NH3)2.H2O簇的两种异构体，约为350厘米-1；对于7HQ.NH3.(H2O)2，约为600厘米-1，但对于纯7HQ.(H2O)3水线簇，阈值增加到约2000厘米-1。为了理解溶剂线的化学成分对氢原子转移的影响，用单激发组态相互作用（CIS）方法计算了n = 3的纯溶剂线簇和混合溶剂线簇的低电子激发态的反应剖面图。对于那些在第一个位置有NH3分子的溶剂线，氢原子可以通过隧穿注入到线中。然而，沿着溶剂线，第一个（和第二个）H2O分子处的高势垒会阻止进一步的氢原子转移。对于任何含H2O的簇，都不会发生沿溶剂线全长的氢原子转移并导致形成7-酮喹啉（7KQ）互变异构体，这与实验观察到的没有7KQ荧光的情况一致。
