Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, USA.
J Phys Chem B. 2010 Nov 18;114(45):14596-604. doi: 10.1021/jp102349m. Epub 2010 Jun 21.
Photophysical studies were performed with Ru(dtb)(2)(dcb)(2) and cis-Ru(dcb)(dnb)(NCS)(2,) where dtb is 4,4'-(C(CH(3))(3))(2)-2,2'-bipyridine, dcb is 4,4'-(COOH)(2)-2,2'-bipyridine, and dnb is 4,4'-(CH(3)(CH(2))(8))(2)-2,2'-bipyridine), anchored to anatase TiO(2) particles (∼15 nm in diameter) interconnected in a mesoporous, thin film (∼10 μm thick) immersed in Li(+)-containing acetonitrile electrolytes. Pulsed-laser excitation resulted in rapid, nonquantitative excited-state injection into TiO(2) with a rate constant that could not be time-resolved, k(inj) > 10(8) s(-1), to yield an interfacial charge-separated state. Return of this state to ground-state products displayed observation-wavelength-dependent kinetics due to charge recombination and a second process. The second process occurred in parallel and was assigned to a transient Stark effect created by the electric field originating from the electrons in TiO(2) on ruthenium sensitizers that had not undergone excited-state injection. The kinetics for this processes were well modeled by a stretched exponential function. The impact of this field on the metal-to-ligand charge transfer excited-state of Ru(dtb)(2)(dcb)(2+) or the oxidized form of cis-Ru(dcb)(dnb)(NCS)(2) were also investigated. Unambiguous identification of a Stark effect on the excited-state sensitizers was accomplished through fluence-dependent measurements. The possible influence of the electric field on the oxidized sensitizers was at best speculative. The unique relative orientation of the electric field and sensitizer afforded by the nanocrystal geometry resulted in unidirectional shifts in the absorption and photoluminescence spectra of the Ru(II) coordination compounds. On the basis of the magnitude of the shift, it was estimated that a transient field as large as 2.7 MV/cm was generated upon excited-state injection of electrons in TiO(2) at concentrations relevant to an operational dye-sensitized solar cell.
采用Ru(dtb)(2)(dcb)(2)和 cis-Ru(dcb)(dnb)(NCS)(2,)作为研究对象，对其光物理性质进行了研究。其中，dtb 为 4,4'-(C(CH(3))(3))(2)-2,2'-联吡啶，dcb 为 4,4'-(COOH)(2)-2,2'-联吡啶，dnb 为 4,4'-(CH(3)(CH(2))(8))(2)-2,2'-联吡啶。这些化合物被锚定在相互连接的介孔薄膜（约 10 μm 厚）中的锐钛矿 TiO(2)颗粒（直径约 15nm）上，薄膜浸于含有锂离子的乙腈电解液中。激光脉冲激发导致快速、非定量的激发态注入 TiO(2)，其速率常数无法进行时间分辨，k(inj) > 10(8) s(-1)，从而产生界面电荷分离态。该状态回到基态产物的过程中，由于电荷复合和第二过程，观察到了依赖于观察波长的动力学。第二过程是平行发生的，并归因于由 TiO(2)中的电子产生的电场引起的瞬态斯塔克效应，该电场作用于尚未经历激发态注入的钌敏化剂。该过程的动力学可以很好地用拉伸指数函数来模拟。还研究了该电场对 Ru(dtb)(2)(dcb)(2+)的金属-配体电荷转移激发态或 cis-Ru(dcb)(dnb)(NCS)(2)的氧化形式的影响。通过依赖于光强的测量，明确地鉴定了斯塔克效应对激发态敏化剂的影响。电场对氧化敏化剂的可能影响最多只是推测性的。纳米晶体几何形状提供的电场和敏化剂的独特相对取向导致 Ru(II)配合物的吸收和光致发光光谱发生单向位移。根据位移的幅度估计，在与工作染料敏化太阳能电池相关的浓度下，电子在 TiO(2)中被激发时，会产生高达 2.7 MV/cm 的瞬态电场。
