Gabrielsson Anders, Busby Michael, Matousek Pavel, Towrie Michael, Hevia Eva, Cuesta Luciano, Perez Julio, Zális Stanislav, Vlcek Antonín
School of Biological and Chemical Sciences, Queen Mary, University of London, Mile End Road, London E1 4NS, United Kingdom.
Inorg Chem. 2006 Nov 27;45(24):9789-97. doi: 10.1021/ic0614768.
UV-vis absorption and picosecond time-resolved IR (TRIR) spectra of amido and phosphido complexes fac-[Re(ER2)(CO)3(bpy)] (ER2 = NHPh, NTol2, PPh2, bpy = 2,2'-bipyridine, Tol = 4-methylphenyl) were investigated in conjunction with DFT and TD-DFT calculations in order to understand their ground-state electronic structure, low-lying electronic transitions and excited-state character and dynamics. The HOMO is localized at the amido/phosphido ligand. Amide and phosphide ligands are sigma-bonded to Re, the pi interaction being negligible. Absorption spectra show a weak band at low energies (1.7-2.1 eV) that arises from essentially pure ER(2) --> bpy ligand-to-ligand charge transfer (LLCT). The lowest excited state is the corresponding triplet, (3)LLCT. Low triplet energies and large distortions diminish the excited-state lifetimes to 85 and 270 ps for NHPh and NTol(2), respectively, and to ca. 30 ps for PPh2. nu(CO) vibrations undergo only very small (<or=10 cm(-1)) shifts upon excitation, attesting to its LLCT character, which hardly affects the electron-density distribution on the Re(CO)3 moiety. Relaxation of the (3)LLCT state occurs with complex dynamics ranging from units to tens of picoseconds. The "pure" LLCT excitation, which does not mix with the Re --> bpy MLCT character, is a unique feature of the amido/phoshido complexes, whose lowest excited state can be viewed as containing a highly unusual aminyl/phosphinyl radical-cationic ligand. For comparison, the amino and phosphino complexes fac-[Re(NHPh(2))(CO)3(bpy)]+ and fac-[Re(PPh3)(CO)3(bpy)]+ are shown to have the usual Re --> bpy (3)MLCT lowest excited states, characterized by upshifted nu(CO) bands.
研究了酰胺基和膦基配合物 fac-[Re(ER2)(CO)3(bpy)]（ER2 = NHPh、NTol2、PPh2，bpy = 2,2'-联吡啶，Tol = 4-甲基苯基）的紫外可见吸收光谱和皮秒时间分辨红外（TRIR）光谱，并结合密度泛函理论（DFT）和含时密度泛函理论（TD-DFT）计算，以了解它们的基态电子结构、低能电子跃迁、激发态性质和动力学。最高占据分子轨道（HOMO）定域在酰胺基/膦基配体上。酰胺和膦配体通过σ键与Re相连，π相互作用可忽略不计。吸收光谱在低能量处（1.7 - 2.1 eV）显示出一个弱带，该弱带基本上源于纯的ER(2)→bpy配体间电荷转移（LLCT）。最低激发态是相应的三重态，即(3)LLCT。较低的三重态能量和较大的畸变分别将NHPh和NTol(2)的激发态寿命缩短至85皮秒和270皮秒，对于PPh2则约为30皮秒。ν(CO)振动在激发时仅发生非常小的（≤10 cm⁻¹）位移，证明其具有LLCT特征，这几乎不影响Re(CO)3部分的电子密度分布。(3)LLCT态的弛豫过程具有从几皮秒到几十皮秒不等的复杂动力学。“纯”LLCT激发不与Re→bpy的金属-配体电荷转移（MLCT）特征混合，这是酰胺基/膦基配合物的独特特征，其最低激发态可视为包含一个非常不寻常的氨基/膦基自由基阳离子配体。作为比较，氨基和膦基配合物fac-[Re(NHPh(2))(CO)3(bpy)]⁺和fac-[Re(PPh3)(CO)3(bpy)]⁺显示具有通常的Re→bpy (3)MLCT最低激发态，其特征是ν(CO)带发生上移。
