Department of Chemistry, University of Rochester , Rochester, New York 14627, United States.
J Am Chem Soc. 2018 Feb 21;140(7):2575-2586. doi: 10.1021/jacs.7b11581. Epub 2018 Feb 8.
Three new dyads consisting of a rhodamine (RDM) dye linked covalently to a Pt diimine dithiolate (PtNS) charge transfer complex were synthesized and used as photosensitizers for the generation of H from aqueous protons. The three dyads differ only in the substituents on the rhodamine amino groups, and are denoted as Pt-RDM1, Pt-RDM2, and Pt-RDM3. In acetonitrile, the three dyads show a strong absorption in the visible region corresponding to the rhodamine π-π* absorption as well as a mixed metal-dithiolate-to-diimine charge transfer band characteristic of PtNS complexes. The shift of the rhodamine π-π* absorption maxima in going from Pt-RDM1 to Pt-RDM3 correlates well with the HOMO-LUMO energy gap measured in electrochemical experiments. Under white light irradiation, the dyads display both high and robust activity for H generation when attached to platinized TiO nanoparticles (Pt-TiO). After 40 h of irradiation, systems containing Pt-RDM1, Pt-RDM2, and Pt-RDM3 exhibit turnover numbers (TONs) of 33600, 42800, and 70700, respectively. Ultrafast transient absorption spectroscopy reveals that energy transfer from the rhodamine π-π* state to the singlet charge transfer (CT) state of the PtNS chromophore occurs within 1 ps for all three dyads. Another fast charge transfer process from the rhodamine π-π* state to a charge separated (CS) RDM-Pt state is also observed. Differences in the relative activity of systems using the RDM-PtNS dyads for H generation correlate well with the relative energies of the CS state and the PtNSCT state used for H production. These findings show how one can finely tune the excited state energy levels to direct excited state population to the photochemically productive states, and highlight the importance of judicious design of a photosensitizer dyad for light absorption and photoinduced electron transfer for the photogeneration of H from aqueous protons.
三个由连接共价键的罗丹明（RDM）染料和一个 Pt 二亚胺二硫代配合物（PtNS）组成的新 dyad 被合成，并被用作从水溶液质子中产生 H 的光催化剂。这三个 dyad 仅在罗丹明氨基上的取代基不同，分别表示为 Pt-RDM1、Pt-RDM2 和 Pt-RDM3。在乙腈中，三个 dyad 在可见区域显示出强烈的吸收，对应于罗丹明π-π吸收，以及混合金属-二硫代配合物到二亚胺电荷转移带，这是 PtNS 配合物的特征。从 Pt-RDM1 到 Pt-RDM3 的罗丹明π-π吸收最大值的位移与电化学实验中测量的 HOMO-LUMO 能隙很好地相关。在白光照射下，当附着在铂化 TiO 纳米粒子（Pt-TiO）上时，dyad 显示出高且稳定的 H 生成活性。照射 40 h 后，含有 Pt-RDM1、Pt-RDM2 和 Pt-RDM3 的系统分别显示出 33600、42800 和 70700 的周转数（TON）。超快瞬态吸收光谱表明，对于所有三个 dyad，从罗丹明π-π态到 PtNS 发色团的单重态电荷转移（CT）态的能量转移在 1 ps 内发生。还观察到从罗丹明π-π态到电荷分离（CS）RDM-Pt 态的另一个快速电荷转移过程。用于 H 生成的 RDM-PtNS dyad 系统的相对活性差异很好地与 CS 态和用于 H 生产的 PtNSCT 态的相对能量相关。这些发现表明如何精细地调节激发态能级以将激发态种群引导到光化学上有生产力的状态，并强调了对于光吸收和光诱导电子转移进行合理设计的重要性，以便从水溶液质子中光生成 H。
