The Influence Of Molecular Modification On The Excited-stated Proton Transfer And Charge Transport Properties Of Organic Polycyclic Heteroaromatics Materials

Generally,the mobilities of organic semiconductors are very low.The proper molecular modification of organic polycyclic heteroaromatics derivative materials would change the photochemical properties and facilitate the charge transport.In this work,we would combine the density functional theory calculation to investigate the reaction mechanism of excited-state proton transfer and charge transport behaviors of organic conjugate systems at room temperature.We would modify the organic molecules with different substituents in different positions to explore the influence of molecular modification on the ESPT reaction,molecular packing and charge transport ability for the organic polycyclic heteroaromatics materials,and then we would find the effective methods for improving the charge mobility as well as stability of organic semiconductor materials.In this thesis,we chose several novel types of organic polycyclic heteroaromatics materials,and systematically investigated and discussed the influence of molecular modification on the reaction mechanism of excited-state proton transfer,the properties of electronic structures as well as charge transport properties.The main research contents and related conclusions of this thesis are as follows:(1)By density functional theory and time-dependent density functional theory methods,we explore the effects of different substitution heterocycles on the excited state intramolecular proton transfer process for three 2-(2’-hydroxybenzofuran)-benzoxazole compounds(HBBX).Via molecular electrostatic potential and reduced density gradient versus sign(λ2)p,we clarify hydrogen bonding effects in three HBBX dyes.Probing into molecular structure and infrared vibrational behaviors,we validate hydrogen bonding O-H…N of HBBX dyes is enhanced in S1 state via photoexcitation.Restructuring of electronic densities provide the impetus for ESIPT reaction of HBBX dyes.Constructing potential energy curves,we confirm ESIPT processes should be more likely to occur in following order:5.560 kcal/mol for HBBX-1>3.451 kcal/mol for HBBX-2>2.240 kcal/mol for HBBX-3,which proves the substitution effects play vital roles in regulating excited state intramolecular proton transfer process for HBBX dyes.(2)The electron-transfer properties for the alkynylated indenofluorene-diones of varying substituents(SiMe3,SiPr3,SiPh3)function as n-type organic semiconductors were comparatively investigated at the first-principle DFT level based on the Marcus-Hush theory to further explore the influence of molecular structure on angular resolution anisotropic mobility.The reorganization energies are calculated by adiabatic potential-energy surface(APES)method,and the coupling terms are evaluated through a direct adiabatic model.The calculated results show that the SiPr3 crystal possesses high intrinsic electron-transfer mobilities.The maximum value of electron-transfer mobility of SiPr3 is 0.485cm2V-1s-1,which appears at the orientation angle of conducting channel on the reference plane a-b near to 172°/352°.The predicted maximum electron mobility value of SiPr3 is nearly 26 times larger than that of SiPh3.This may be attributed to the largest number of intermolecular π-πinteractions.The calculated results indicate that SiPr3 could be an ideal candidate as a high-performance n-type organic semiconductor material.(3)Theoretical investigations of hole-transport properties in two naphtha[2,1-b:6,5-b’]difuran derivatives as novel p-type organic semiconductor based on the Marcus-Hush theory combining the first principle quantum mechanics are carried out.This work focuses on the effects of carbon chain on molecular orbitals,partial charge difference,ionization potential,internal energy relaxation,and hole-transport behaviors.Through computational modeling,we are shedding light on the favorable function of C8-DPNDF single crystal as p-type organic material.With the introduction of octyl group,C8-DPNDF single crystal possesses high hole-transfer mobilites(1.589 cm2V-1s-1)and remarkable anisotropic behavior.The simulated anisotropic mobility curve of C8-DPNDF demonstrates the maximum value of the mobility appears when the measuring conducting channel is along the b-axis of the single crystal.The adiabatic ionization potential(AIP)and vertical ionization potential(VIP)of C8-DPNDF are about 6.312 eV and 6.399 eV,that is,slightly smaller than those of DPNDF.The relatively small ionization potential values can ensure effective hole injection from the source electrode.The data obtained from the present work can be used to prove that C8-DPNDF molecule has the potential to develop into high-efficient p-type organic semiconductor materials,whose hole-transport mobility can be further improved when the measuring transistor channel is controlled carefully.(4)We theoretically investigated the charge transport properties in bisindenoanthrazoline-based n-type organic semiconductors at the first-principle DFT level based on the Marcus-Hush theory.The relationship between molecular packing and charge transport for DADF and DADK was presented.We theoretically demonstrated that DADK single crystal possesses considerable electron-transfer mobility,which is about 3 times larger than that of DADF.In addition,the angle dependence of mobility in all two crystals shows remarkable anisotropic behavior,although the crystals are of different geometries as a novel n-type bisindenoanthrazilines(BIDAs)organic semiconductor.The predicted maximum electron mobility value of DADK is 0.373 cm2V-1s-1,which appears at the orientation angle near to 72°/252° of conducting channel on the reference plane a-c.The calculated results indicate that DADK may be an ideal candidate as a high-performance n-type organic semiconductor material.The experimental result also demonstrated that the molecular geometry of organic semiconductor plays an important role in determining the molecular stacking,electronic properties,and charge transport behaviors.