Excited State Proton Transfer Study On Two Kinds Of Dyestuff Molecules

TDDFT and DFT calculations have been employed to research proton transfer on two type of molecules,which are 2-（（5（1H-benzo[d]imidazol-2-yl）-imino）methyl）-5-（dimethylamino）-phenol（BIP）and 1,5-dihydroxyanthranthraquinone（1,5-DHAQ）.The main works are presented as follows:There are two type structures for BIP,the BIP-enol and BIP-keto.These two structures were optimized by DFT and TDDFT methods,B3 LYP hybrid exchange functional and TZVP basis set.The infrared spectra、frontier molecular orbital and potential energy curves are calculated.The schematic diagram of dynamic process for BIP sensor in both S0 and S1 states were analyzed.In view of the solvent effect,acetonitrile is used as solvent throughout.The study indicates:（1）The intramolecular hydrogen bond（O₁-H₂...N₃）is strengthened in the S1,this will facilitate ESIPT process.（2）The infrared spectra 、 absorption spectra and fluorescence spectra are in consistent with the experiment,which illustrate the method we selected is correct.The change of electron density can promote excited state proton transfer.（3）The calculated S1 potential energy curve is almost flat,so the proton can easily cross the potential barrier.In other words,the proton transfer process should be more likely to occur in the S1 state.The 1,5-DHAQ molecular is optimized by using DFT/B3LYP/TZVP and TDDFT/B3LYP/TZVP theory methods.The absorption spectra、infrared vibrational spectra、dual fluorescence spectra and Raman spectra,the frontier molecular orbital and potential energy surfaces are calculated.Ethanol is used as the solvent.The results are:（1）By comparing with the staple bond lengths and bond angles involved in the hydrogen bonding,it is revealed that the intramolecular hydrogen bond is strengthened in the S1 state.（2）The infrared spectra 、 absorption spectra 、 fluorescence spectra and dualfluorescence are in consistent with the experiment,which illustrate the method we selected is correct.Raman spectra for enol and keto configurations illuminate that the intramolecular hydrogen bonds should be strengthened in the S1 state.The change of electron density can enhance intramolecular hydrogen bonding,which may promote the ESIPT process.（3）The bond energies of these stable structures on the S0,S1 and triple states are calculated,it is found that the bond energy for the keto configuration of the S1 and triplet is larger than for the enol form,that is to say,PT may take up in these structures.（4）By calculating the PESs in the S₀,S₁ and triplet states,we find that the excited-state single and dual PT processes can occur in the S1 state.Furthermore,the excited-state single PT process also can take up in the triplet state.