The Theory Study Of The Hydrogen Bond Effects In Excited State Of Organic Molecular Systems In Water

The solute-solvent interactions play a fundamental role on the photochemistry ofcomplex molecular systems in solution, particularly, intermolecular hydrogen bonding.However, intermolecular hydrogen bonding is how affecting photochemistry behavior? Itrequires researchers to explore dynamical behaviors of hydrogen bonds in electronic excitedstates plays an important role on the photochemistry and radiative relaxation processes ofelectronic from ground states to excited states in hydrogen bonding complexes. Therefore, wefocus on that dynamical behavior of hydrogen bonds in electronic excited states in solution.In paper, hydrogen bonded NMF-(H2O)2,3and MDMAB-(H2O)n(n=1,2,3) complexeshave been investigated by quantum chemical calculations. The ground state geometric carriedout using density functional theory (DFT) method. The time dependent density functionaltheory (TDDFT) method has become a useful tool for calculating the electronic excitationenergies and the absorption spectra in electronically excited states. The result showed that fivehydrogen-bonded complexes be formed between the isolated NMF molecular and two or threewater molecular. The hydrogen bonds are strengthened in the electronically excited state, andhydrogen bonds C=O H-O are most strengthened. The C=O group takes an active part informing of hydrogen-bonded, and shows strong hydrogen donor ability. Thehydrogen-bonded complexes compared with the isolated NMF molecular, which leads to ared-shift in the electronic absorption spectrum. Two types hydrogen bonds such asC=O H-O and C-O H-O can be formed between MDMAB and H2O. The intermolecularhydrogen bonds C=O H-O and C-O H-O are significantly strengthened in the excited state.The hydrogen bond complexes induced an obvious red-shift compared with the isolatedMDMAB molecular in absorption spectra. However, our calculated results are in accordancewith the hydrogen bonding strengthening mechanism in the electronically excited state. Thesestudies also enriched the theory of excited hydrogen bond strengthening.