Theoretical Studies Of The Intermolecular Hydrogen Bonding Of Two Derivatives Of Carbazole

The intermolecular or intramolecular weak interaction plays a very important role in physics,chemistry,biology and many other areas.Such as molecular fluorescence quenching,excited state proton transfer,phase change materials and intermolecular charge transfer process,etc.Class carbazole and its derivatives is a kind of very important nitrogenous aromatic heterocyclic structure molecules containing large conjugated system and strong intramolecular electron transfer.Carbazole derivatives can easily form intermolecular hydrogen bond with some polar solvent under the condition of the optical excitation.These features have become a research topic in recent years.Samita Basu measured spectrum of MTC?5-Methoxy-1-keto-1,2,3,4-tetrahydro Carbazole?and TDCO?5,6,7,9-tetrahydro-[1,3]dioxolo[4,5-h]carbazol-8-one?in different solvents,and pointed out that red shift of MTC and TDCO spectrum in polar solvent is caused by hydrogen bonding effect,but hydrogen bonding mechanism on the red shift of MTC and TDCO spectrum is not clear yet.In this article,density functional theory?DFT?and time-dependent density functional theory?TDDFT?quantum chemistry methods are employed to simulate the spectrum of MTC and TDCO hydrogen bonding system,and to deeply study the hydrogen bonding effects on the ground state and excited state of MTC and TDCO,aiming to establish hydrogen bonding interaction mechanism on carbazole derivative spectrum frequency shift.Firstly,DFT and TDDFT method with functional B3LYP,CAM/B3LYP,PBE0 are used to theoretical simulate absorption spectrum of MTC monomer,MTC-H₂O,MTC-ethanol hydrogen bonding complexes,and functional B3LYP is selected for the following theoretical computations by comparing the obtained theoretical simulate absorption spectrum with experimental data of Samita Basu.Ground state and excited state's geometry optimization,infrared spectrum,corresponding electronic excitation energy,absorption spectrum and fluorescence spectrum of MTC monomer,MTC hydrogen bonding complexes,and TDCO hydrogen bonding complexes are calculated.Theoretical absorption and fluorescence spectrum show red shift due to the formation of hydrogen bonds,which are in accordance with the experimental results of Samita Basu,Secondly,due to the deviation of theoretical absorption and fluorescence spectrum of MTC-H₂O hydrogen bonding complex with the experimental results of Samita Basu,a large number of simulation of absorption and fluorescence spectrum of MTC-?H₂O?n are carried out and the results show that the simulated spectrum of MTC-?H₂O?₃ accords better with the Samita Basu's experimental results.Moreover,further study on MTC-?H₂O?n complexes with same amount of water molecules but different position to form hydrogen bonds geometry shows that the main factor that influence the fluorescence spectrum of MTC-?H₂O?n complexes is the number of hydrogen bonds formed at C=O group.Solvent polarity has margin influence on absorption spectra of TDCO hydrogen bonding complexes.For hydrogen bonding complexes formed by TDCO and water,and TDCO and ethanol molecules,the absorption spectrum and fluorescence spectrum have a red shift due to the formation of hydrogen bonds,which show that hydrogen bonds in excited states are strengthened.