Department of Chemistry, IIT Hyderabad, Kandi, Sangareddy, Telangana 502285, India.
Department of Chemistry, IIT Hyderabad, Kandi, Sangareddy, Telangana 502285, India.
Spectrochim Acta A Mol Biomol Spectrosc. 2022 Oct 5;278:121285. doi: 10.1016/j.saa.2022.121285. Epub 2022 Apr 28.
The role of solvent molecules in the deactivation of photo-excited 2,7-diazaindole (DAI) - (HO) and DAI - (NH) complexes were computationally investigated. An excited-state proton transfer (ESPT) path from the solvent to the DAI molecule was followed using the TD-DFT-D4 (B3LYP) level of theory. The computed potential energy profile of ESPT process has shown intersection between ππ* and nπ* states facilitated via relative stabilization of the nπ* state with decreasing N(7)-H bond length. The ESPT process, starting from the DAI-S (ππ*) state, crosses through a barrier ranging from 27 to 36 kJmol for water complexes and 26-30 kJmol for ammonia complexes. The energy of the excited state was rapidly decreased with a shorter N(7)-H bond length. Subsequently, a significant trend of finding a second intersection between the ground and the excited state was observed for all the complexes. The results firmly suggested a significant deactivation channel of excited azaindole derivatives. In the present system, two competing channels, ESPT and ESHT, were found to be energetically accessible. The energy barriers associated with the ESPT barriers for DAI-(HO) complexes are similar to the ESHT barrier, depicting equal dominance of both processes. The increased basicity of the N(7) atom in the excited state resulted a facile ESPT process from the water to N(7) of the DAI molecule. However, DAI-(NH) complexes show clear preference for ESHT over ESPT process owing to its higher gas-phase pK value making it a poor proton donor. The above systems can be used as a model to computationally and experimentally investigate the competing radiative and deactivation pathways of photo-excited solvated complexes of N-H-bearing bio-relevant molecules via proton and hydrogen transfer reactions.
溶剂分子在光激发的 2,7-二氮杂吲哚（DAI）-（HO）和 DAI -（NH）配合物失活中的作用通过计算进行了研究。使用 TD-DFT-D4（B3LYP）理论水平跟踪了从溶剂到 DAI 分子的激发态质子转移（ESPT）路径。ESPT 过程的计算势能曲线表明，随着 N(7)-H 键长的减小，nπ* 态的相对稳定促进了 ππ* 和 nπ* 态之间的交叉。ESPT 过程从 DAI-S（ππ*）态开始，穿过一个从 27 到 36 kJmol 的势垒，对于水配合物，和 26-30 kJmol 对于氨配合物。激发态的能量随着 N(7)-H 键长的缩短而迅速降低。随后，对于所有配合物，观察到基态和激发态之间存在第二个交叉的显著趋势。结果有力地表明了激发的氮杂吲哚衍生物的显著失活通道。在本系统中，发现两个竞争通道，ESPT 和 ESHT，在能量上是可及的。对于 DAI-(HO) 配合物，与 ESPT 势垒相关的能量势垒与 ESHT 势垒相似，表明两个过程都具有同等的主导地位。由于在激发态下 N(7)原子的碱性增加，因此从水中到 DAI 分子的 N(7)的 ESPT 过程变得容易。然而，由于 DAI-(NH) 配合物的气相 pK 值较高，使其成为一个较差的质子供体，因此其对 ESHT 过程的偏好明显超过 ESPT 过程。上述系统可作为模型，通过质子和氢转移反应，计算和实验研究含 N-H 的生物相关分子的光激发溶剂配合物的竞争辐射和失活途径。
