El-Zohry Ahmed M, Agrawal Saurabh, De Angelis Filippo, Pastore Mariachiara, Zietz Burkhard
Department of Chemistry, Ångström Laboratories, Box 523, SE-75120 Uppsala, Sweden.
Department of Physics-AlbaNova Universitetscentrum, Stockholm University, SE-10691 Stockholm, Sweden.
J Phys Chem C Nanomater Interfaces. 2020 Oct 1;124(39):21346-21356. doi: 10.1021/acs.jpcc.0c07099. Epub 2020 Sep 8.
By combining time-correlated single photon counting (TCSPC) measurements, density functional theory (DFT), and time-dependent DFT (TD-DFT) calculations, we herein investigate the role of protons, in solutions and on semiconductor surfaces, for the emission quenching of indoline dyes. We show that the rhodanine acceptor moieties, and in particular the carbonyl oxygens, undergo protonation, leading to nonradiative excited-state deactivation. The presence of the carboxylic acid anchoring group, close to the rhodanine moiety, further facilitates the emission quenching, by establishing stable H-bond complexes with carboxylic acid quenchers, with high association constants, in both ground and excited states. This complexation favors the proton transfer process, at a low quencher concentration, in two ways: bringing close to the rhodanine unit the quencher and assisting the proton release from the acid by a partial-concerted proton donation from the close-by carboxylic group to the deprotonated acid. Esterification of the carboxylic group, indeed, inhibits the ground-state complex formation with carboxylic acids and thus the quenching at a low quencher concentration. However, the rhodanine moiety in the ester form can still be the source of emission quenching through dynamic quenching mechanism with higher concentrations of protic solvents or carboxylic acids. Investigating this quenching process on mesoporous ZrO, for solar cell applications, also reveals the sensitivity of the adsorbed excited rhodanine dyes toward adsorbed protons on surfaces. This has been confirmed by using an organic base to remove surface protons and utilizing cynao-acrylic dye as a reference dye. Our study highlights the impact of selecting such acceptor group in the structural design of organic dyes for solar cell applications and the overlooked role of protons to quench the excited state for such chemical structures.
通过结合时间相关单光子计数（TCSPC）测量、密度泛函理论（DFT）和含时密度泛函理论（TD-DFT）计算，我们在此研究了溶液中和半导体表面的质子对吲哚啉染料发射猝灭的作用。我们表明，若丹宁受体部分，特别是羰基氧，会发生质子化，导致非辐射激发态失活。靠近若丹宁部分的羧酸锚定基团的存在，通过在基态和激发态与羧酸猝灭剂形成具有高缔合常数的稳定氢键复合物，进一步促进了发射猝灭。这种络合作用以两种方式有利于在低猝灭剂浓度下的质子转移过程：使猝灭剂靠近若丹宁单元，并通过附近羧基向去质子化酸的部分协同质子供体作用协助质子从酸中释放。事实上，羧基的酯化抑制了与羧酸的基态络合物形成，从而抑制了低猝灭剂浓度下的猝灭。然而，酯形式的若丹宁部分在较高浓度的质子溶剂或羧酸存在下，仍可通过动态猝灭机制成为发射猝灭的来源。在用于太阳能电池应用的介孔ZrO上研究这种猝灭过程，还揭示了吸附的激发若丹宁染料对表面吸附质子的敏感性。这已通过使用有机碱去除表面质子并使用氰基丙烯酸染料作为参考染料得到证实。我们的研究强调了在用于太阳能电池应用的有机染料结构设计中选择此类受体基团的影响，以及质子对猝灭此类化学结构激发态的被忽视的作用。
