Synthesis Of Liquid Crystal Porphyrin Derivatives And Application As Photovoltaic Materials

Porphyrin derivatives are a kind of compounds possessing large ? conjugated cycle.They have excellent planarity and favourable spectral absorption in the visible light region.So they have been studied as functional organic materials in recent years.Up to now,researchers have designed and synthesized various porphyrin derivatives as organic optoelectronic materials.These porphyrin derivatives are mainly used in the following aspects: 1)research on the photovoltaic performance used as organic photovoltaic cell materials;2)research on the luminescence properties used as organic electroluminescent materials;3)research on the photosensitive property used as organic photoconductive materials,etc.These prophyrin derivatives used as organic optoelectronic functional materials are limited to crystalline and amorphous state from the perspective of the condensed state of molecules.In order to make full use of the excellent optoelectronic properties of porphyrin derivatives and expand the application prospect as functional orgainc materials,the research of porphyrin derivatives with liquid crystalline property is a meaningful topic.In this paper,the author have designed and synthesized a series of symmetrical structure porphyrin derivatives,5,10,15,20-tetra-(4-carbomethoxyphenyl)porphyrin(TCMPP),5,10,15,20-tetra(4-carboxylphenyl)porphyrin(TCPP),5,10,15,20-tetra-(4-acylaminophenyl)porphyrin(4NCn-TPP,n = 8,10,14,16,18)and their Zinc complexes 4NCn-TPPZn.They were characterized using mass spectra(MS),nuclear magnetic resonance(NMR)and Fourier Transform Infrared Spectroscopy(FI-IR).The related molecule structures are shown as follows:The optical and electrical properties of porphyrin derivatives were investigated by UV-vis absorption spectra(UV-vis),fluorescence spectra(FL)and cyclic voltammetry(CV).The maximum absorption wavelength,low-energy absorption edge,fluorescence emissionwavelength and the redox potentials were determined.The optical band gap,HOMO/LUMO levels and electrochemical band gap of these porphyrin derivatives were calculated.And the relation between the length of side chains as well as the complexation of Zinc atom and the photoelectric property of porphyrin derivatives were analyzed.The results of the study showed that the length of the side chain substituents had little influence on the UV-vis absorption and the redox potentials.However,the UV-vis absorption of Zinc coordinated porphyrin complexes had been broaden and had a few red shift,and the introduction of the metal atom decreased the electrochemical band gap.The thermal properties of porphyrin derivatives were studied by Thermogravimetry(TG)and Differential Scanning Calorimetry(DSC).The morphology of the films of porphyrin derivatives were studied using Polarizing Optical Microscopy(POM)and X-ray diffraction(XRD).TG results showed that the decomposition temperature of porphyrin derivatives were high,and they had good thermal stability.The DSC results of porphyrin ligands showed that4NC8-TPP and 4NC10-TPP only had fusion and crystallization peaks and glass transition.However,the DSC curves of 4NCn-TPP(n = 14,16,18)not only had clearing point and melting point,but also had glass transition.The observation results from POM showed that4NCn-TPP(n = 14,16,18)had fanshaped and flower-like liquid crystalline texture cooling from the isotropic state.The study also found that the range of liquid crystalline increased with the increase of the alkyl chains.The DSC results of Zinc porphyrin complexes showed that they all had one pair of melting and crystallization peaks.This results indicated that porphyrin derivatives no longer had liquid crystalline property after coordinated with Zinc atom.According to the POM images of porphyrin complexes,they showed only dendritic or spherical crystal cooling from isotropic state.The XRD results indicated that the films of porphyrin ligands did not show diffraction peaks and they tended to be amorphous phase.However,after coordinated with metal atom the XRD showed obvious diffraction peaks which indicated that the porphyrin complexes had better crystallinity.Using the porphyrin derivatives we have synthesized as electron donor materials and perylene-3,4,9,10-tetracarboxylic dianhydride(PTCDA)as acceptor material,organic bulk heterojunction photovoltaic devices were fabricated through vacuum evaporation.ITO glass and Al were used as anode and cathode,respectively.The structure of the devices was ITOglass/porphyrin derivatives:PTCDA/Al.The photoelectric conversion efficiency(PCE)was tested.The influence of morphology on the photovoltaic property was investigated.The results showed that althrough 4NC14-TPP,4NC16-TPP and 4NC18-TPP had liquid crystalline property,the films prepared through vacuum evaporation tended bo be amorphous phase in room temperature.Nevertheless,the films of porphyrin complexes had better crystallization phase.The crystalline morphology of the film had better molecule orientation which benefit the separation and transmission of electrons and holes.The active layers of devices were observed using Atomic Force Microscope(AFM).The results showed that the molecule orientation of the bulk heterojunction films of porphyrin complexes with PTCDA was better than that of porphyrin ligands with PTCDA.Therefore,the PCEs of the devices prepared by porphyrin complexes were higher than that of porphyrin ligands.