Solvent assisted excited-state deactivation pathways in isolated 2,7-diazaindole-S1-3 (S = Water and Ammonia) complexes

Roy Chowdhury, P. and Khodia, S. and Maity, Surajit (2022) Solvent assisted excited-state deactivation pathways in isolated 2,7-diazaindole-S1-3 (S = Water and Ammonia) complexes. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 278. pp. 1-10. ISSN 1386-1425

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The role of solvent molecules in the deactivation of photo-excited 2,7-diazaindole (DAI) – (H2O)1-3 and DAI – (NH3)1-3 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)-Hb bond length. The ESPT process, starting from the DAI-Sn (ππ*) state, crosses through a barrier ranging from 27 to 36 kJmol−1 for water complexes and 26–30 kJmol−1 for ammonia complexes. The energy of the excited state was rapidly decreased with a shorter N(7)-Hb 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-(H2O)1-3 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-(NH3)1-3 complexes show clear preference for ESHT over ESPT process owing to its higher gas-phase pKa 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. © 2022 Elsevier B.V.

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IITH Creators:
IITH CreatorsORCiD
Maity, Surajit
Item Type: Article
Additional Information: SK thanks MoE, the Government of India, for the fellowship. PRC and SM thanks IIT Hyderabad and SERB, DST for fellowship. Funding: This work was supported by SERB, DST, Government of India (Grant no. CRG/2019/003335)
Uncontrolled Keywords: Excited-state hydrogen atom transfer, Excited-state proton transfer, Hydrogen bonding, Isolated micro-solvated molecular clusters, Non-radiative Photo-deactivation, Potential energy surface, Reaction pathway
Subjects: Chemistry
Divisions: Department of Chemistry
Depositing User: . LibTrainee 2021
Date Deposited: 17 Jun 2022 10:35
Last Modified: 22 Jun 2022 07:25
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