Papa Christopher M, Garakyaraghi Sofia, Granger Devin B, Anthony John E, Castellano Felix N
Department of Chemistry , North Carolina State University , Raleigh , North Carolina 27695-8204 , USA . Email:
Department of Chemistry , University of Kentucky , Lexington , Kentucky 40506-0055 , USA.
Chem Sci. 2020 May 18;11(22):5690-5696. doi: 10.1039/d0sc00310g. eCollection 2020 Jun 14.
Many fundamental questions remain in the elucidation of energy migration mechanisms across the interface between semiconductor nanomaterials and molecular chromophores. The present transient absorption study focuses on PbS quantum dots (QDs) of variable size and band-edge exciton energy (ranging from 1.15 to 1.54 eV) post-synthetically modified with a carboxylic acid-functionalized TIPS-pentacene derivative (TPn) serving as the molecular triplet acceptor. In all instances, selective excitation of the PbS NCs at 743 nm leads to QD size-dependent formation of an intermediate with time constants ranging from 2-13 ps, uncorrelated to the PbS QD valence band potential. However, the rate constant for the delayed formation of the TPn triplet excited state markedly increases with increasing PbS conduction band energy, featuring a parabolic Marcus free energy dependence in the normal region. These observations provide evidence of an indirect triplet sensitization process being inconsistent with a concerted Dexter-like energy transfer process. The collective data are consistent with the generation of an intermediate resulting from hole trapping of the initial PbS excited state by midgap states, followed by formation of the TPn triplet excited state whose rate constant and yield increases with decreasing quantum dot size.
在阐明半导体纳米材料与分子发色团之间界面的能量迁移机制方面，仍存在许多基本问题。目前的瞬态吸收研究聚焦于可变尺寸且带边激子能量范围为1.15至1.54 eV的硫化铅量子点（QDs），这些量子点在合成后用作为分子三重态受体的羧酸官能化的TIPS-并五苯衍生物（TPn）进行了修饰。在所有情况下，在743 nm处对硫化铅纳米晶体进行选择性激发会导致形成一种中间体，其时间常数范围为2至13 ps，且与硫化铅量子点的价带电位无关，该中间体的形成与量子点尺寸有关。然而，TPn三重态激发态延迟形成的速率常数随着硫化铅导带能量的增加而显著增加，在正常区域呈现抛物线型的马库斯自由能依赖性。这些观察结果提供了证据，表明间接三重态敏化过程与类似德克斯特协同能量转移过程不一致。总体数据与由中间能隙态对初始硫化铅激发态进行空穴俘获产生中间体，随后形成TPn三重态激发态一致，其速率常数和产率随着量子点尺寸的减小而增加。
