Intermolecular Hydrogen Bonding Tunes Vibronic Coupling in Heptazine Complexes
Intermolecular Hydrogen Bonding Tunes Vibronic Coupling in Heptazine Complexes
复制标题
分子间氢键调节七嗪配合物中的电子振动耦合
DOI：
10.1021/acs.jpcb.0c07719
复制
发表时间：
2020
期刊：
影响因子：
--
通讯作者：
Schlenker, Cody W.
中科院分区：
文献类型：
--
作者：
Rabe, Emily J.;Goldwyn, Harrison J.;Hwang, Doyk;Masiello, David J.;Schlenker, Cody W.
为了更好地了解氢键如何影响氮杂芳烃材料的激发态景观，我们研究了与石墨化氮化碳相关的分子光催化剂2，5，8-Tris(4-methoxyphenyl)-1，3，4，6，7，9，9b-heptaazaphenalene(TAHZ)与多种苯酚衍生物(R-PhOH)的氢键配合物。通过改变苯酚上对位取代基的吸电子特性，我们可以调节氢键的强度。利用时间分辨光致发光，我们提取了与R-PhOH-TAHZ氢键络合物相关的光谱分量。令人惊讶的是，我们注意到在以太赫兹为中心的发射中，振动峰的相对幅度随着苯酚上R基团的变化而发生了显著的变化。为了获得对这些光谱变化的物理理解，我们使用了分子发射的位移振子模型来拟合这些光谱。这种拟合假定两个振动模主要耦合到发射电子跃迁，并提取它们的频率和相对核位移(与黄-里斯因子有关)。在量子化学计算的帮助下，我们发现七嗪环呼吸和环折叠模式很可能是导致观察到的振动级数的原因，并且这两种模式都表明分子在激发态的扭曲程度随着氢键强度的增加而减小。这一发现为分子间激发态氢键提供了新的见解，这是控制激发态质子耦合电子转移和质子转移反应的关键一步。
To better understand how hydrogen bonding influences the excited-state landscapes of aza-aromatic materials, we studied hydrogen-bonded complexes of 2,5,8-tris (4-methoxyphenyl)-1,3,4,6,7,9,9b-heptaazaphenalene (TAHz), a molecular photocatalyst related to graphitic carbon nitride, with a variety of phenol derivatives (R-PhOH). By varying the electron-withdrawing character of the para-substituent on the phenol, we can modulate the strength of the hydrogen bond. Using time-resolved photoluminescence, we extract a spectral component associated with the R-PhOH-TAHz hydrogen-bonded complex. Surprisingly, we noticed a striking change in the relative amplitude of vibronic peaks in the TAHz-centered emission as a function of R-group on phenol. To gain a physical understanding of these spectral changes, we employed a displaced-oscillator model of molecular emission to fit these spectra. This fit assumes that two vibrational modes are dominantly coupled to the emissive electronic transition and extracts their frequencies and relative nuclear displacements (related to the Huang–Rhys factor). With the aid of quantum chemical calculations, we found that heptazine ring-breathing and ring-puckering modes are likely responsible for the observed vibronic progression, and both modes indicate decreasing molecular distortion in the excited state with increasing hydrogen bond strength. This finding offers new insights into intermolecular excited-state hydrogen bonding, which is a crucial step toward controlling excited-state proton-coupled electron transfer and proton transfer reactions.