Investigation On The Photophysical Propetries Of Organic Photoelectric Material

The organic photoelectric materials are widely used in organic light emittingdiode, organic transistor, organic solar cell, an organic memory and so on, due toeasy processing, fast optical response and high storage density. There are somecommonality and difference in these applications. The commonality is thatsemiconductor optoelectronic properties of these material are used to improveperformance response. The difference is that the different of the performancematerial requires different chemical structure to achieve. So we can see that there isa close relationship between performance and molecular structure. To study theserelationships can help us to design and optimize new materials, explore noveldevices.In this thesis, we study explicitly ultrafast optical dynamics and nonlinearoptical properties of three kinds of optoelectronic materials by absorptionspectroscopy, fluorescence spectroscopy, femtosecond pump-probe technique,z-scan and so on. The main research results are as follows:1. We systemically study the photophysical properties of the low bandgappolymer based on poly-thienothiophhene diketopyrrolopyrrole-thiophene(PDPPTT-T) in the solution and the solid film by experimental and theoreticalmethods. The experimental results show that relaxation mechanism of excitedpolymer in the solution is the intrachain exciton relaxation and vibrationalrelaxation at the lower intensity, and at the higher intensity the exciton-excitonannihilation(EEA) would appear; while in the solid film is consisted of theexciton relaxation. The quantum chemical calculations show the molecularground state structure, the corresponding orbital information and the electronictransition mechanism. At the same time, the quantum chemical calculations also show that in experimental absorption spectra the lowest energy band isassigned to S0â†'S1the transition featuring Ï€â†'Ï€*transition.2. We systemically study the photophysical properties of the two D-A typecopolymers with the different ratios between donor and acceptor unit(fluorene-carbazole unit as donor and benzothiadiazole moiety as acceptor,PCFBT) in the solution by experimental and theoretical methods. Theexperimental results show when the number of donor is equal to that ofacceptor in one repeat unit, the intrachain charge transfer (ICT) could occurand participate in the relaxation of excited state after photoexcitation. Whenthe number of donor is much larger than that of acceptor in one repeat unit, theintrachain exciton decay process would be dominant in the relaxation of thecopolymer, which also involves an excitation intensity-independent vibrationalthermal relaxation process at the initial time. The quantum chemical resultsshow the molecular ground state structure, the corresponding orbitalinformation and the electronic transition mechanism, which is good agreementwith the experimental results.3. We explicitly study the fluorene-vinylene unit dependent photo-physicalproperties of multi-branched truxene based oligomers (Tr-OFVn(n=1-4)) in thesolution by theoretical and experimental methods. The experimental resultsshow that the extension of Ï€ conjugated system leads to the increasing of themolar absorption coefficient and the enhancement of the single-photonfluorescence intensity, and shortens the excited state species lifetime.Meanwhile, two-photon fluorescence (TPF) efficiency and two-photonabsorption (TPA) cross section of truxene based oligomers gradually enhancesin company with the extension of Ï€-conjugated length. The quantum chemicalresults promote the understanding of the molecular ground state structure, the corresponding orbital information and the electronic transition mechanis m.