Hodgkiss Justin M, Damrauer Niels H, Pressé Steve, Rosenthal Joel, Nocera Daniel G
Department of Chemistry, 6-335, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139-4307, USA.
J Phys Chem B. 2006 Sep 28;110(38):18853-8. doi: 10.1021/jp056703q.
The temperature-isotope dependence of proton-coupled electron transfer (PCET) for a noncovalent molecular dyad is reported. The system consists of an excited-state Zn(II) porphyrin that transfers an electron to a naphthalene diimide acceptor through an amidinium-carboxylate interface. Two different isotope effects are observed for variant temperature regimes. A reverse isotope effect (i.e., kH/kD < 1) is observed as T approaches 120 K (kH/kD = 0.9, 120 K), whereas a normal isotope effect (i.e., kH/kD > 1) is recovered as the temperature is increased (kH/kD = 1.2, 300 K). The transition between these limits is smooth, with a crossover temperature of T approximately 160 K. These observations are in accordance with charge-transfer dynamics that are susceptible to bath-induced fluctuations in the proton coordinate.
报道了一种非共价分子二元体系中质子耦合电子转移（PCET）的温度-同位素依赖性。该体系由一个激发态的Zn（II）卟啉组成，它通过脒基-羧酸盐界面将一个电子转移到萘二酰亚胺受体上。在不同的温度范围内观察到两种不同的同位素效应。当温度接近120K时，观察到反向同位素效应（即kH/kD < 1）（kH/kD = 0.9，120K），而当温度升高时则恢复正常同位素效应（即kH/kD > 1）（kH/kD = 1.2，300K）。这些极限之间的转变是平滑的，交叉温度约为160K。这些观察结果与电荷转移动力学一致，电荷转移动力学易受质子坐标中浴致波动的影响。
