Theoretical Study On Excited State Intramolecular Proton Transfer Of HPIP And HPIP's Derivatives

Excited state intramolecular proton transfer(ESIPT)means that the proton occur transfer from an atom to another atom,when the molecule at excited-state.Exploring the ESIPT properties of molecules will help people understand its micro-physical mechanisms,design and develop new luminescent materials.We probed into the effect of the substituents position and solvent polarity on HPIP,5'Br-HPIP and 6'Br-HPIP.We analyzed the ESIPT characteristics of HPIP,5'Br-HPIP and 6'Br-HPIP,respectively.From the results,the ESIPT emission peak of5'Br-HPIP was 573nm,the ESIPT emission value of HPIP was 602nm,and the6'Br-HPIP ESIPT fluorescence was 640nm.At the same time,the ESIPT fluorescence intensity was increased from HPIP to 6'Br-HPIP to 5'Br-HPIP.The charge distribution indicates that the electrical negativity of N₁atoms in 5'Br-HPIP was stronger than those in 6'Br-HPIP,thus attracting H₁more easily when compared to 6'Br-HPIP.The N-H bond peak of 5'Br-HPIP was less than that of 6'Br-HPIP,meaning that5'Br-HPIP were more prone to ESIPT processes.We found that the energy level of the 5'Br-HPIP molecule is lager than that of the 6'Br-HPIP molecule,so the ESIPT fluorescence peak of the 5'Br-HPIP was 573nm,6'Br-HPIP was 640nm.And the interaction between the N₁atom and the H₁atom in the 5'Br-HPIP molecule is stronger than 6'Br-HPIP.The ESIPT process is easier to occur.In addition,we calculated the ESIPT fluorescence characteristics of 6'Br-HPIP molecules in different solvents(water,THF and TL).From the results,we found that in water,the ESIPT fluorescence peak of 6'Br-HPIP was 580nm,which was smallest in three solvent.And the fluorescence intensity was strongest in three solvent.The electronegativity of N₁atom in 6'Br-HPIP was gradually enhanced and it was easier to attract H₁,so the 6'Br-HPIP molecules are more likely to undergo ESIPT processes in highly polar solvent environments.According to the calculation results,it can be seen that the energy level of the 6'Br-HPIP molecule was largest in water,so the ESIPT emission peak of the 6'Br-HPIP molecule was changed.And the 6'Br-HPIP is easier to occur ESIPT process in high polar solvent.