Han Xue, Wu Li-Zhu, Si Gang, Pan Jie, Yang Qing-Zheng, Zhang Li-Ping, Tung Chen-Ho
Technical Institute of Physics and Chemistry, The Chinese Academy of Sciences, Beijing 100080, P. R. China.
Chemistry. 2007;13(4):1231-9. doi: 10.1002/chem.200600769.
A series of platinum(II) terpyridyl alkynyl complexes, [Pt{4'-(4-R1-C6H4)terpy}(C[triple chemical bond]C-C6H4-R(2)-4)]ClO4 (terpy=2,2':6',2''-terpyridyl; R1=R2=N(CH3)2 (1); R1=N(CH3)2, R2=N-[15]monoazacrown-5 (2); R1=CH3, R2=N(CH3)2 (3); R1=N(CH3)2, R2=H (4); R1=CH3, R2=H (5)), has been synthesized and the photophysical properties of the complexes have been examined through measurement of their UV/Vis absorption spectra, photoluminescence spectra, and transient absorptions. Complex 3 shows a lowest-energy absorption corresponding to a ligand-to-ligand charge-transfer (LLCT) transition from the acetylide to the terpyridyl ligand, whereas 4 shows an intraligand charge-transfer (ILCT) transition from the pi orbital of the 4'-phenyl group to the pi* orbital of the terpyridyl. Upon protonation of the amino groups in 3 and 4, their lowest-energy excited states are switched to dpi(Pt)-->pi*(terpy) metal-to-ligand charge-transfer (MLCT) states. The lowest-energy absorption for 1 and 2 may be attributed to an LLCT transition from the acetylide to the terpyridyl. Upon addition of an acid to a solution of 1 or 2, the amino group on the acetylide is protonated first, followed by the amino group on the terpyridyl. Thus, the lowest excited state of 1 and 2 can be successively switched from the LLCT state to the ILCT state and then to the MLCT state by controlling the amount of the acid added. Such switches in the excited state are fully reversible upon subsequent addition of a base to the solution. Sequential addition of alkali metal or alkaline earth metal ions and then an acid to a solution of 2 also leads to switching of its lowest excited state from the LLCT state, first to the ILCT state and then to the MLCT state. All of the complexes exhibit a transient absorption of the terpyridyl anion radical, which is present in all of the LLCT, ILCT, and MLCT states. However, the shape of the transient absorption spectrum depends on both the substitution pattern on the terpyridyl moiety and the nature of the excited state.
一系列铂（II）三联吡啶炔基配合物，[Pt{4'-(4-R1-C6H4)三联吡啶}(C≡C-C6H4-R2-4)]ClO4（三联吡啶=2,2':6',2''-三联吡啶；R1=R2=N(CH3)2 (1)；R1=N(CH3)2，R2=N-[15]单氮杂冠-5 (2)；R1=CH3，R2=N(CH3)2 (3)；R1=N(CH3)2，R2=H (4)；R1=CH3，R2=H (5)）已被合成，并通过测量其紫外/可见吸收光谱、光致发光光谱和瞬态吸收来研究这些配合物的光物理性质。配合物3显示出对应于从乙炔基到三联吡啶配体的配体间电荷转移（LLCT）跃迁的最低能量吸收，而配合物4显示出从4'-苯基的π轨道到三联吡啶的π轨道的配体内电荷转移（ILCT）跃迁。当配合物3和4中的氨基质子化时，它们的最低能量激发态转变为dpi(Pt)→π(三联吡啶)的金属到配体电荷转移（MLCT）态。配合物1和2的最低能量吸收可能归因于从乙炔基到三联吡啶的LLCT跃迁。向1或2的溶液中加入酸时，乙炔基上的氨基首先质子化，随后是三联吡啶上的氨基。因此，通过控制加入酸的量，配合物1和2的最低激发态可以依次从LLCT态转变为ILCT态，然后再转变为MLCT态。在随后向溶液中加入碱时，这种激发态的转变是完全可逆的。向配合物2的溶液中依次加入碱金属或碱土金属离子，然后再加入酸，也会导致其最低激发态从LLCT态依次转变为ILCT态，然后再转变为MLCT态。所有配合物都表现出三联吡啶阴离子自由基的瞬态吸收，该自由基存在于所有的LLCT、ILCT和MLCT态中。然而，瞬态吸收光谱的形状既取决于三联吡啶部分的取代模式，也取决于激发态的性质。
