The Effects Of Conjugated Molecular Structures On Absorption Spectra And The Charge Transport Of Perovskite

?-conjugated organic dye molecules have some prominent advantage including large molar absorbance in visible-near infrared(NIR)spectral range,flexible structures to be chemically tailored and low price,et al.Dye molecules can absorb photons and generate fluorescence or phosphor luminescence through radiative transition,or conver them into electric energy or heat energy by other different non-radiative transition pathways.Therefore,as bulk materials or a component of organic-inorganic hybrid materials,dye molecules have become a research hotspot in the field of new optoelectronic devices and light energy conversion.Photothermal diagnosis and treatment is to convert absorbed photons into heat energy or phonons in the form of thermal radiation,so as to generate local high temperature,achieve imaging at designated sites,or induce apoptosis or necrosis of cancer cells.The design and synthesis of dye molecules with strong absorption and stable to light and heat in the NIR region is the key to the realization of NIR photothermal diagnosis and treatment.Perylene diimide(PDI)derivatives have high molar absorbance coefficient and fluorescence quantum efficiency in the visible region,high thermal-and photo-stability,and the molecular framework has multiple modifiable sites for functionalization,which showed great potential for development of photothermal treatment agent.The main way to improve the photothermal conversion efficiency of PDI is to optimize the molecular structure of PDI and make it have strong absorption in the NIR window.Studies on NIR photoacoustic imaging using PDI derivatives have been reported recently,but there are few reports on its structure design in NIR photothermal therapy.Organic halide perovskite structure is a kind of organic-inorganic hybrid material which has been developed rapidly in recent years,and has attracted much attention as optoelectronic device materials,especially solar cell materials.Among the many factors that affect the structure and photoelectric properties of perovskite halide,charge transport is one of the most essential factors that determine its performance.The introduction of T?-conjugated small molecules can effectively regulate the crystal structure,stability and other basic characteristics of lead halide perovskite.Also,novel and unique perovskite structure can be expected,of which the light absorption and charge transfer characteristics can be regulated through the synergistic effect of organic-inorganic components.The effect of 7E-conjugated molecules on charge transport in perovskite structures remains to be disclosed.In this thesis,the relationship between molecular structure and absorption spectrum of PDI derivatives as photothermal conversion materials,and charge transport properties of organic lead halide perovskite structures constructed from naphthalimide(NDIA)derivatives was investigated respectively by theoretical calculation based on the experimental results.Two parts of researches are included:1.PDI-6 molecule with strong absorption in NIR region was synthesized and encapsulated in silica nanocapsule to obtain PDI@SiO2 NC with high NIR photothermal conversion efficiency.The effect of different positions of substitution on the absorption spectrum of PDI derivatives was studied by Gaussion simulation,aiming to guide the design of NIR absorbing PDI molecules for further enhancement of photothermal conversion efficiency.A series of PDI derivatives were designed and synthesized,and the following rules were obtained according to their spectral absorption experimental results and theoretical calculation results:electron-donating group on bay-substituent makes the HOMO level rise,leading to the red shift of the main absorption peak;a substituent group conjugated with the perylene ring results in a decrease of the LUMO level and further red shift of the absorption spectrum;sulfur substitution on carbonyl leads to a decrease in the LUMO level and thus redshift in the absorption spectrum;when the donor group participates in the conjugation of perylene ring skeleton,the weak n-?*transition with lower energy than HOMO-LUMO transition occurs,which makes the position of absorption peak red-shift further.In the PDI-11 structure,the ln-?*transition overlaps with the ?-?*,transition,which makes the absorption red shift with enhanced intensity.2.One dimensional(NDIA)2Pb2Br6 single crystal structure was prepared by introducing NDIA into perovskite halide structure.The FET curves of the devices made from(NDIA)2Pb2Br6 show excellent balanced p-and n-polarity,and the mobility is up to 6 Cm2V-v-1S-1.In order to explore the relationship between the structure and charge transfer,the theoretical simulation was carried out by using Vienna ab inito simulation package(VASP)on the basis of single crystal structure.According to the calculated results of band structure and DOS,the effective mass of 0.02 mo is obtained,which is the main cause of such high carrier mobility.To further understand the effect of the organic molecule on charge transport,the band structure of the organic and inorganic parts were calculated respectively,and the preliminary charge transport mechanism of(NDIA)2Pb2Br6 structure was put forward.