Indelli Maria Teresa, Chiorboli Claudio, Flamigni Lucia, De Cola Luisa, Scandola Franco
Dipartimento di Chimica, Università di Ferrara, 44100 Ferrara, Italy.
Inorg Chem. 2007 Jul 9;46(14):5630-41. doi: 10.1021/ic700430u. Epub 2007 Jun 12.
A series of rodlike ruthenium(II)-rhodium(III) polypyridine dyads based on modular oligo-p-phenylene bridges, of the general formula [(Me2phen)2Ru-bpy-(ph)n-bpy-Rh(Me2bpy)]5+ (Me2phen=4,7-dimethyl-1,10-phenanthroline; bpy=2,2'-bipyridine; ph=1,4-phenylene; n=1-3), have been synthesized and their photophysical properties investigated. The dyad [(Me2bpy)2Ru-bpy-(ph)3'-bpy-Rh(Me2bpy)]5+ with the central phenylene unit bearing two hexyl chains has also been studied. The metal-to-metal distance reaches 24 A for the longest (n=3) spacer in the series. For all of the dyads in a room-temperature CH3CN solution, quenching of the typical metal-to-ligand charge-transfer luminescence of the Ru-based chromophoric unit is observed, indicating that an efficient intramolecular photoinduced electron transfer from the excited Ru moiety to the Rh-based unit takes place. The rate constants for the electron-transfer process have been determined by time-resolved emission and absorption spectroscopy in the nanosecond and picosecond time scale. An exponential dependence of experimental transfer rates on the bridge length is observed, consistent with a superexchange mechanism. An attenuation factor beta of 0.65 A(-1) is determined, in line with the behavior of other systems containing oligo-p-phenylene spacers. Interestingly, for n=3, the presence/absence of hexyl substituents in the central p-phenylene ring causes a 10-fold difference in the rates between otherwise identical dyads. This comparison highlights the importance of the twist angle between adjacent spacers on the overall through-bond donor-acceptor coupling.
基于模块化低聚对亚苯基桥的一系列通式为[(Me2phen)2Ru-bpy-(ph)n-bpy-Rh(Me2bpy)]5+（Me2phen = 4,7-二甲基-1,10-菲咯啉；bpy = 2,2'-联吡啶；ph = 1,4-亚苯基；n = 1 - 3）的棒状钌（II）-铑（III）多吡啶二元化合物已被合成，并对其光物理性质进行了研究。还研究了中心亚苯基单元带有两条己基链的二元化合物[(Me2bpy)2Ru-bpy-(ph)3'-bpy-Rh(Me2bpy)]5+。该系列中最长（n = 3）间隔基的金属-金属距离达到24 Å。对于室温下CH3CN溶液中的所有二元化合物，观察到Ru基发色单元典型的金属-配体电荷转移发光猝灭，表明发生了从激发的Ru部分到Rh基单元的有效分子内光诱导电子转移。通过纳秒和皮秒时间尺度的时间分辨发射和吸收光谱法测定了电子转移过程的速率常数。观察到实验转移速率对桥长度呈指数依赖性，这与超交换机制一致。确定衰减因子β为0.65 Å(-1)，这与其他含有低聚对亚苯基间隔基的系统的行为一致。有趣的是，对于n = 3，中心对亚苯基环中己基取代基的存在与否导致在其他方面相同的二元化合物之间速率有10倍的差异。这种比较突出了相邻间隔基之间的扭转角对整体通过键供体-受体耦合的重要性。
