McGarrah James E, Eisenberg Richard
Department of Chemistry, University of Rochester, Rochester, New York 14627-0216, USA.
Inorg Chem. 2003 Jul 14;42(14):4355-65. doi: 10.1021/ic034026d.
The platinum diimine bis(acetylide) chromophore was utilized to explore photoinduced intramolecular reductive quenching with phenothiazine donors in chromophore-donor dyad complexes. Compounds of the general formula Pt(X(2)-bpy)(C triple bond C-p-C(6)H(4)CH(2)(D))(2) (where D = phenothiazine (PTZ) or trifluromethylphenothiazine (TPZ) and X = (t)Bu or CO(2)Et) were synthesized from the corresponding Pt(X(2)-bpy)Cl(2) and aryl acetylene by a CuI-catalyzed coupling reaction. Solvent dependence was explored for the system with X = (t)Bu in MeCN, CH(2)Cl(2), EtOAc, and toluene. Electron transfer quenching of the (3)MLCT excited state of the platinum diimine bis(acetylide) takes place in MeCN leaving no intrinsic emission from the excited state, but in toluene both the PTZ and TPZ dyad complexes exhibit no emission quenching. Picosecond pump-probe transient absorption (TA) experiments were used to monitor decay of the (3)MLCT excited state and electron transfer to form the charge-separated (CS) state. Electrochemical measurements were used to estimate the driving force for charge recombination (CR), with deltaE(CR) based on the reduction potential corresponding to Pt(X(2)-bpy)(C triple bond C-Ar)(2) --> Pt(X(2)-bpy()(-))(C triple bond C-Ar)(2) and the oxidation corresponding to donor --> donor()(+). Kinetic information from the TA measurements was used to correlate rate and driving force with the electron transfer reactions. Concomitant with the decay of the (3)MLCT excited state was the observation of a transient absorption at ca. 500 nm due to formation of the PTZ or TPZ radical cation in the CS state, with the rate of charge separation, k(CS), being 1.8 x 10(9) to 2 x 10(10) s(-1) for the three dyads explored in MeCN and 1:9 CH(2)Cl(2)/MeCN. The fastest rate of CR occurs for X = CO(2)Et and D = PTZ, the compound with smallest deltaE(CR) = 1.71 V. The rate of CR for dyads with X = (t)Bu and D = PTZ or TPZ was estimated to be 1.7-2.0 x 10(8) s(-1) in MeCN. The slower rate corresponds to a greater driving force for CR, deltaE(CR) = 2.18 and 2.36 V for D = PTZ and TPZ, respectively, suggesting that the driving force for charge recombination places it in the Marcus inverted region.
铂二亚胺双（乙炔基）发色团被用于研究发色团 - 供体二元配合物中与吩噻嗪供体的光诱导分子内还原猝灭。通式为Pt(X(2)-bpy)(C≡C-p-C(6)H(4)CH(2)(D))(2)（其中D = 吩噻嗪（PTZ）或三氟甲基吩噻嗪（TPZ）且X = (t)Bu或CO(2)Et）的化合物由相应的Pt(X(2)-bpy)Cl(2)和芳基乙炔通过碘化亚铜催化的偶联反应合成。研究了X = (t)Bu的体系在乙腈、二氯甲烷、乙酸乙酯和甲苯中的溶剂依赖性。铂二亚胺双（乙炔基）的(3)MLCT激发态在乙腈中发生电子转移猝灭，激发态没有固有发射，但在甲苯中，PTZ和TPZ二元配合物均未表现出发射猝灭。利用皮秒泵浦 - 探测瞬态吸收（TA）实验监测(3)MLCT激发态的衰减以及电子转移形成电荷分离（CS）态。电化学测量用于估计电荷复合（CR）的驱动力，基于对应于Pt(X(2)-bpy)(C≡C - Ar)(2)→Pt(X(2)-bpy()(-))(C≡C - Ar)(2)的还原电位和对应于供体→供体()(+)的氧化电位计算ΔE(CR)。来自TA测量的动力学信息用于将速率和驱动力与电子转移反应相关联。伴随(3)MLCT激发态的衰减，观察到在约500 nm处有瞬态吸收，这是由于CS态中PTZ或TPZ自由基阳离子的形成，在所研究的乙腈和1:9二氯甲烷/乙腈中的三种二元配合物中，电荷分离速率k(CS)为1.8×10(9)至2×10(10) s(-1)。对于X = CO(2)Et且D = PTZ的化合物，CR速率最快，其ΔE(CR)最小，为1.71 V。在乙腈中，X = (t)Bu且D = PTZ或TPZ的二元配合物的CR速率估计为1.7 - 2.0×10(8) s(-1)。较慢的速率对应于更大的CR驱动力，对于D = PTZ和TPZ，ΔE(CR)分别为2.18和2.36 V，这表明电荷复合的驱动力使其处于马库斯反转区域。
