The Research Of The Excited-state Intra- And Inter- Molecular Hydrogen Bond Dynamics As Well As Proton Transfer Reaction

Hydrogen bond, as one of the most significant weak interactions, is omnipresent in nature, based on which life-cycle can be sustained in the world. It plays instrumental roles in many photo-chemistry, photo-physics or biochemical processes, which has became the nucleus of polyhedral research activities. No matter the intermolecular hydrogen bonds or intramolecular hydrogen bonds are becoming very attractive, which plays important roles in photo-chemical and photo-physical reactions such as fluorescence quenching, intermolecular charge transfer(ICT), photo-induced electron transfer(PET), fluorescence resonance energy transfer(FRET), excited-state proton-transfer(ESPT) and so forth. Proton transfer is one of the most important reactions in chemical and biological acid-base dynamics resulting from site-specific interactions through hydrogen bond. Particularly, excited state proton transfer have many applications such as: the design and use of fluorescence sensors, laser dyes and LEDs, UV filters, molecular switches and so forth.In the present work, all the theoretical calculations presented were accomplished using DFT and TDDFT methods with Becke’s three-parameter hybrid exchange function with the Lee-Yang-Parr gradient-corrected correlation functional(B3LYP) based on the Gaussian 09 programs. We mainly focus on discussing three systems containing excited state double proton transfer in detail. “A questionable excited-state double proton transfer mechanism for 3-hydroxyisoquinoline.”, “New excited-state proton transfer for 1,8-dihydroxdibenzo[a,h]phenazine.” and “Competitive excited state single or double proton transfer mechanism for bis-2,5-(2-benzoxazolyl)- hydroquinone and its derivatives.” The potential energy surfaces of S0 and S1 states have been constructed to reject the structural attribution of 3-hydroxyisoquinoline in previous experimental work for the first time. Particularly, we put forward a new mechanism about the excited state double proton transfer of 3-hydroxyisoquinoline dimer. In addition, the same approach of constructing potential energy surfaces has been adopted to replenish the insufficient about excited state proton transfer mechanism of DHBP molecular. Also a new excited state proton transfer mechanism has been put forward. Finally, we find the conclusion of single excited state proton transfer is always drawn based on the nodal plane model in previous works. However, no specific potential energy barriers can be obtained based on the nodal plane model, so whether the conclusion of only a single proton transfer is correct based on the nodal plane model warrants further attention. Therefore, we constructed the potential energy surfaces to investigate the excited state proton transfer of BBHQ and DHBO moleculars in detail. Finally, a new mechanism differs from the one proposed previously is proposed, which includes the possibility of simultaneous double proton transfer and successive single proton transfer. In conclusion, our investigations not only testify the rationality and efficiency of the calculated method we applied, but also explain and propose the new excited state double proton transfer mechanism based on constructed potential energy surfaces.