Lainé Philippe P, Bedioui Fethi, Loiseau Frédérique, Chiorboli Claudio, Campagna Sebastiano
Laboratoire de Chimie et Biochimie Pharmacologiques et Toxicologiques, CNRS UMR-8601, Université René Descartes, 45 rue des Saints Pères, F-75270 Paris Cedex 06, France.
J Am Chem Soc. 2006 Jun 14;128(23):7510-21. doi: 10.1021/ja058357w.
(ttpy)Os(tpy-ph-TPH(3)(+)) (2), (ttpy)Os(tpy-xy-TPH(3)(+)) (3), (ttpy)Os(tpy-ph-TPH(2)(NO(2))(+)) (4), and (ttpy)Os(tpy-xy-TPH(2)(NO(2))(+)) (5) are a series of dyads made of an Os(II) bis-tpy complex (tpy = 2,2':6',2"-terpyridine) as the photosensitizer (P) and 2,4,6-triarylpyridinium group (TP(+)) as the electron acceptor (A). These dyads were designed to form charge-separated states (CSS) upon light excitation. Together with analogous Ru(II) complexes (7-10), they have been synthesized and fully characterized. We describe herein how intramolecular photoinduced processes are affected when the electron-accepting strength of A (by nitro-derivatization of TP(+)) and/or the steric hindrance about intercomponent linkage (by replacing a phenyl spacer by a xylyl one) are changed. Electronic absorption and electrochemical behavior revealed that (i) chemical substitution of TP(+) (i.e., TP(+)-NO(2)) has no sizable influence on P-centered electronic features, (ii) reduction processes located on TP(+) depend on the intercomponent tilt angle. Concerning excited-state properties, photophysical investigation evidenced that phosphorescence of P is actually quenched in dyads 4 and 5 only. Ultrafast transient absorption (TA) experiments allowed attributing the quenching in conformationally locked dyad 5 to oxidative electron transfer (ET) from the (3)MLCT level to the TP(+)-NO(2) acceptor (k(el) = 1.1 x 10(9) s(-)(1)). For 4, geometrically unlocked, the (3)MLCT state was shown to first rapidly equilibrate (reversible energy transfer; k(eq) approximately 2 x 10(9) s(-)(1)) with a ligand centered triplet state before undergoing CSS formation. Thus, the pivotal role of conformation in driving excited-state decay pathways is demonstrated. Also, inner P structural planarization as a relaxation mode of the (3)MLCT states has been inferred from TA experiments.
(ttpy)Os(tpy - ph - TPH(3)(+))（2）、(ttpy)Os(tpy - xy - TPH(3)(+))（3）、(ttpy)Os(tpy - ph - TPH(2)(NO(2))(+))（4）和(ttpy)Os(tpy - xy - TPH(2)(NO(2))(+))（5）是由作为光敏剂（P）的Os(II)双 - tpy配合物（tpy = 2,2':6',2'' - 三联吡啶）和作为电子受体（A）的2,4,6 - 三芳基吡啶鎓基团（TP(+)）组成的一系列二元化合物。这些二元化合物旨在在光激发时形成电荷分离态（CSS）。它们与类似的Ru(II)配合物（7 - 10）一起被合成并得到了全面表征。我们在此描述当A的电子接受强度（通过TP(+)的硝基衍生化）和/或组分间连接的空间位阻（通过用二甲苯基取代苯基间隔基）发生变化时，分子内光诱导过程是如何受到影响的。电子吸收和电化学行为表明：（i）TP(+)的化学取代（即TP(+) - NO(2)）对以P为中心的电子特征没有显著影响，（ii）位于TP(+)上的还原过程取决于组分间的倾斜角。关于激发态性质，光物理研究证明只有在二元化合物4和5中P的磷光实际上被猝灭。超快瞬态吸收（TA）实验表明，构象锁定的二元化合物5中的猝灭归因于从(3)MLCT能级到TP(+) - NO(2)受体的氧化电子转移（ET）（k(el) = 1.1×10(9) s(-)(1)）。对于几何结构未锁定的4，(3)MLCT态在形成CSS之前首先与配体中心三线态快速达到平衡（可逆能量转移；k(eq)约为 = 2×10(9) s(-)(1)）。因此，证明了构象在驱动激发态衰变途径中的关键作用。此外，从TA实验推断出内部P结构平面化是(3)MLCT态的一种弛豫模式。
