Dipartimento di Scienze Chimiche, Università di Padova, via Marzolo 1, 35131 Padova, Italy.
CNR-ISMN, Istituto per lo Studio dei Materiali Nanostrutturati, c/o Dipartimento di Scienze Chimiche, Biologiche, Farmaceutiche ed Ambientali, V.le F. Stagno D'Alcontres 31, 98166 Messina, Italy.
J Chem Phys. 2021 Feb 28;154(8):084201. doi: 10.1063/5.0038242.
The influence of hydrogen bonds (H-bonds) in the structure, dynamics, and functionality of biological and artificial complex systems is the subject of intense investigation. In this broad context, particular attention has recently been focused on the ultrafast H-bond dependent dynamical properties in the electronic excited state because of their potentially dramatic consequences on the mechanism, dynamics, and efficiency of photochemical reactions and photophysical processes of crucial importance for life and technology. Excited-state H-bond dynamics generally occur on ultrafast time scales of hundreds of femtoseconds or less, making the characterization of associated mechanisms particularly challenging with conventional time-resolved techniques. Here, 2D electronic spectroscopy is exploited to shed light on this still largely unexplored dynamic mechanism. An H-bonded molecular dimer prepared by self-assembly of two boron-dipyrromethene dyes has been specifically designed and synthesized for this aim. The obtained results confirm that upon formation of H-bonds and the dimer, a new ultrafast relaxation channel is activated in the ultrafast dynamics, mediated by the vibrational motions of the hydrogen donor and acceptor groups. This relaxation channel also involves, beyond intra-molecular relaxations, an inter-molecular transfer process. This is particularly significant considering the long distance between the centers of mass of the two molecules. These findings suggest that the design of H-bonded structures is a particularly powerful tool to drive the ultrafast dynamics in complex materials.
氢键（H-bonds）在生物和人工复杂体系的结构、动力学和功能中的影响是一个研究热点。在这个广泛的背景下，由于它们对光化学反应和光物理过程的机制、动力学和效率可能产生的巨大影响，人们最近特别关注电子激发态中超快的 H 键依赖性动力学特性，这些过程对生命和技术至关重要。激发态 H 键动力学通常发生在数百飞秒或更短的超快时间尺度上，这使得用传统的时间分辨技术来表征相关机制具有特别的挑战性。在这里，二维电子光谱被用来揭示这个仍然很大程度上未被探索的动态机制。为了实现这一目标，专门设计并合成了由两个硼二吡咯甲川染料自组装而成的氢键分子二聚体。所得结果证实，在形成氢键和二聚体后，超快动力学中会激活一个新的超快弛豫通道，由氢供体和受体基团的振动运动介导。这种弛豫通道还涉及除了分子内弛豫之外的分子间转移过程。考虑到两个分子的质心之间的长距离，这一点尤其重要。这些发现表明，设计氢键结构是驱动复杂材料中超快动力学的一种特别有力的工具。
