The Theoretical Evaluation Of The State Of The Fluorescent Probe's Solvent Discoloration Ability Specifies The Electrostatic Potential Molecular Descriptor

Lippert-Mataga equation is widely used to describe the solvatochromic effects of fluorescent probe molecules.This equation is mainly based on the point-dipole approximation model to describe the interaction between solute and solvent.The gap between dipole deviation of molecule in the ground-state and the lowest excited-state is regarded as basic requirement to the design of a polarity-sensitive fluorescent probe.However,some recently synthesized probes with the center-symmetry have near zero dipole deviation while undergoing notably solvatochromic behaviors.It is obviously unreasonable to use the Lippert-Mataga equation to describe the solvatochromic phenomenon of such molecules.It is necessary to find a new method to qualitatively estimate the molecular solvent shift beyond Lippert-Mataga model.In this paper,a novel state-specific electrostatic potential descriptor(SSD)is proposed based on the surface electrostatic potential to evaluate the solvatochromic ability of coumarin C153 and the central symmetry molecule DCB-1d.In contrast to the experimental solvent shifts and TD-DFT calculations,the SSD successfully explain the solvatochromic effect of C153 and DCB-1d molecules.To this end,a new state-specific electrostatic potentials descriptor(SSD)based on molecular surface electrostatic potentials(ESP)is proposed to estimate the solvatochromic behaviors of well-studied coumarin C153 and center-symmetric DCB-1d.In addition,another thirteen molecules with typical solvatochromic effect were selected as test objects.It was found that SSD has a good linear relationship with the solvatochromic ability of molecular emission spectra.At the same time,the non-equilibrium implicit solvation model was used to calculate the internal reorganization energy and external reorganization energy of coumarin C153 and the central symmetric molecule DCB-1d in different polar solvents,and successfully evaluated spectral spread width of these two molecules according to reorganization energy.The details are as follows:In chapter one,the application of fluorescent probe molecules is briefly introduced,which leads to the important position of fluorescent probes in the fields of biology,materials and environment due to the characteristics of their molecular systems.The polar sensitive probe molecules are highlighted.The principle of solvatochromism of probe molecules in different polar solvents and its research progress are listed.The detailed description is given.The molecular spectrum is reflected by its broadening width,stokes displacement,internal and solvation reorganization energy,and the difference between the molecular excited state and the ground state structure.The molecular spectrum can reflect the difference between the excited state and the ground state structure.It can reflect the interaction strength through the broadening width,stokes shift.So the spectral broadening width,internal reorganization energy and solvation reorganization energy are also briefly introduced.In chapter two,the basic theory used in the research work of this thesis is introduced.The principle of Lippert-Mataga equation,which is the basis of the solvatochromism of polar sensitive probe molecule,is briefly introduced.Non-equilibrium solvation model,the basic model used in the study of solvent effect is introduced.State-specific solvation effect are introduced,the concept,principle and descriptor of electrostatic potential descriptor is also briefly introduced.In chapter three,in view of the shortcomings of Lippert-Mataga equation,the basic principle of the new state-specified electrostatic potential molecular descriptor(SSD)is introduced.Under the inspiration of the electrostatic potential descriptor developed by Politzer,combined with the classical solvent reaction field theory,a new state-specified electrostatic potential descriptor(SSD)was developed to evaluate the solvatochromic effect of the probe molecule.The fluorescent probe molecule coumarin C153 and the central symmetric molecule DCB-1d were used to study the solvatochromism and spectrum under different polar solvents,which confirmed that the new state-specific electrostatic potential descriptor(SSD)can be used to evaluate solvatochromism.The dipole moment variation and the average electrostatic potential deviation(?)are also calculated.Comparing the calculation results of these three methods with the experimental values,it can be seen that the SSD method can better explain solvatochromism of the coumarin C153 and the central symmetric molecule DCB-1d.In order to verify whether the SSD evaluates molecular solvatochromism,another thirteen solvatochromic probes were selected as the research object,and the solvatochromic effect was evaluated by SSD.It is found that there is a good linear relationship between SSD and Av,indicating that SSD can correctly describe the solvatochromic effect of the probe molecule during absorption and emission.In chapter four,the coumarin C153 and the central symmetric molecule DCB-1d were mainly studied.Based on the normal analysis mode,the four-point method,the non-equilibrium implicit solvation model,and the improved Marcus broadening formula,the calculation of two probes was proposed.The internal reorganization energy,solvation reorganization energy(external reorganization energy),absorption and emission spectral broadening of C153 and DCB-ld in different solvents were calculated in detail.And these results were analyzed and discussed.