The Novel Imidazole Based Conjugated Materials:Design,Synthesis And Properties Investigation

Organic conjugated material has many merits,such as flexible,lightness,wet processability,easily tunable optoelectronic properties and low cost.Thus,its development and application has been paid much attention by the scientific community and industry.Organic conjugated material consists of conjugated units with the highly delocalized ? system and the closed shell structure.It is one of the most important ways to tune and optimize optical and electronic properties of the material by design and synthesis of novel conjugated unit.Imidazole ring is a 6 electron 5 atom conjugate system,which contains a pyridine-typed N and a pyrrole-typed N.This special five-membered conjugated system with dual nitrogen atoms gives excellent optoelectronic and semiconducting properties.In this thesis,pyrene-fused bisimidazole were synthesized.To explore the potential of this novel unit in conjugated materials,conjugated small molecules and polymers was synthesized.Organic field effect transistors(OFET)based on these materials were also fabricated.The pyrene-fused bisimidazole based conjugated mesoporous polymer was synthesized and properties were studied.Additionally,the imidazole based exited state intramolecular proton transfer(ESIPT)compound was synthesized and the photophysical properties were investigated.The details are as follows:1.We fused two imidazole rings at K-region of pyrene with a symmetrical manner to form a novel fused polycyclic building block,pyrene-fused bisimdazole.In order to explore the application of this structure in the field of soluble small molecule semiconductor,PBI-L-Na and PBI-B-Na were synthesized.In the conjugated system,pyrene-fused bisimdazole unit was characterized by rigidity,coplanarity and large conjugation.Due to steric hindrance,the alkyl side chains on the pyrene-fused bisimdazole exhibited a twisted structure with respect to the conjugate plane.UV-Vis spectra,electrochemical measurements,X-ray diffraction experiments and OFET device performance showed that the photoelectric properties of these materials were seriously affected by the alkyl chains.With the small linear side chains,PBI-L-Na was able to form a more ordered stacking structure with a conjugate plane spacing of 0.36 nm.The OFET device exhibited a hole mobility of 0.12 cm2 V-1 s-1.The bulky branch side chains impeded the ?-? interaction between the conjugated planes.Thus,the hole mobility of PBI-B-Na is only 4.6×10-3 cm2 V-1 s-1.2.In order to expolre the potential of pyrene-fused bisimdazole in polymeric systems,two conjugated copolymers of pyrene-fused bisimdazole(PBTI)with vinylene(P1)or thiophene(P2)were synthesized by stille coupling reaction.Their semiconducting properties were investigated by UV-Vis spectra,electrochemical measurements and OFET devices.Both polymers exhibited highly coplanar backbones,similar lowest unoccupied molecular orbital energy levels at-3.7 eV and the uniform delocalized highest occupied molecular orbital with deep-lying energy levels around-5.7 eV.X-ray diffraction and grazing-incident X-ray diffraction measurements demonstrated that P2 adopted a highly ordered structure,thus giving an enhanced hole mobility of 0.015 cm2 V-1 s-1 in organic thin film transistors.3.We investigated the possibility of Debus-Radziszewski reaction in the preparation of conjugated porous polymer,and synthesized conjugated mesoporous polymer(PI-CMP)based on pyrene-fused bisimidazole.IR,XPS and elemental analysis indicated the feasibility of Debus-Radziszewski reaction in the preparation of conjugated porous polymer.Thermal analysis showed that the thermal decomposition temperature of PI-CMP was as high as 608 ?.SEM and TEM photographs showed the cross-linked morphology of PI-CMP materials and the stacked structure of conjugated planes.The specific surface area of PI-CMP was 477 m2 g-1,and the pore size distributes in the range of 3.5 nm(this value is close to the theoretical value of 3.9 nm).Using three-electrode system,the potential of PI-CMP in application of super-capacitor was explored.4.The novel ESIPT molecule(E1)based on tetraphenylimidazole was designed and synthesized,and the methoxy substituted molecule M1 was investigated as enol form molecule.The UV-Vis absorption,fluorescence spectra and fluorescence decay curves of M1 and E1 were used to study the phenomenon and mechanism of ESIPT.In the case of ESIPT,the E1 molecule had a large Stokes shift of more than 180 nm,and effectively limited the energy transfer between the fluorescent dyes.The ESIPT process involves multiple states.As the polarity of the solvent increased,the effect of the solvent molecules on the enol form and ketone form excited states was gradually enhanced.In the acetonitrile,a highly polar solvent,the interaction of the solvent molecule on enol form excited state directly blocked the ESIPT process.