Dynamic Effects Of Hydrogen Bonding On Intramolecular And Intermolecular Proton Transfer

The hydrogen bonding (H-bond) interaction occupies an important post in many biological macromolecules, chemical complexes and physical processes. And, the existence of the hydrogen bond, which is unambiguous and enormous for sustaining the life-cycle in the natural system, is universal and inevitable. It has been confirmed to be very important link of the molecular non-equilibrium processes in solution. Hydrogen bonds can exist in the molecules as well as between molecules. Lately, researchers proposed a new reaction mechanism which is called electronic-state hydrogen bonding dynamics.They pointed out that the change of hydrogen bond in the excited state can inhibit or promote the proton transfer (PT) process. Since then, the investigations of the intramolecular and intermolecular hydrogen bonds in the excited state are prominent based on various experimental and theoretical methods. So far, the reaction mechanism made a further explanation for the intramolecular charge transfer (ICT), photoinduced electron transfer (PET), fluorescence resonance energy transfer (FRET) and excited state proton transfer (ESPT), and so on. In particular, the excited-state intramolecular proton transfer (ESIPT) or intermolecular proton transfer have been favored by researchers. After the excited-state proton transfer, the target molecules can produce isomers, which attract people to design them and apply to the UV filters, laser dyes and LEDs molecular, etc. Therefore, a large number of the theoretical and experimental studies on proton transfer are ongoing.This article mainly discusses the choice of three molecular systems to do the corresponding research:the detailed theoretical investigation of excited-state intramolecular proton transfer mechanism of a new chromophore II (the synthesis and characteristics of aromatic hydrazones based on 2-hydroxy-l-naphthaldedhyde and salicylaldehyde), the investigation of excited-state intramolecular proton transfer mechanism of 1-morpholinylmethyl-2-naphthol and the excited-state multiple proton transfer mechanism of 7-hydroxquinoline-(CH3OH)3 cluster. We used the density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods, B3LYP functional, TZVP basis set and 6-31+G(d) basis set,respectively, to optimizate the configurations of diferent molecular systems. In addition, we also calculated the corresponding spectra (the absorption spectrum, fluorescence spectrum and infrared spectroscopy), so as to determine whether the results of our theoretical calculation is consistent with the experimental results. Finally, we scanned the potential energy curves combining with the change of hydrogen bonds in ground state and excited state to judge whether the proton transfer can occur. Particllarly, we again to investigate the excited-state multiple proton transfer mechanism of 7-hydroxquinoline-(CH3OH)3 cluster in detail. And, We found that the 7HQ-(CH3OH)3-PT form can exist. What excites us is that the two types (TypeA and Type B) of proton transfer mechanisms are coexist competitively through analyzing the corresponding potential energy curves. This new mechanism is put forward, of course, we also hope it can be supported by the subsequent experiment data.