Investigation On The Photophysical Properties Of D-?-A Style Organic Oligomers By Using Ultrafast Spectroscopy

With the continuous development of scientific research,we have discovered the intrinsic link between the physical nature of light and electricity,and we also find they can transform from each other under certain conditions.Since the 1980 s,a new type of material has begun to dominate the material science,and such material is the organic optoelectronic material.The emergence of such new materials has promoted the interdisciplinary integration of materials,electronics,chemistry,information and energy,and has led to a variety of new interdisciplinary disciplines,such as optoelectronics and organic electronics.Organic photoelectric materials include functional polymers and organic small molecular materials.These new materials have many advantages.Because organic photoelectric materials are a kind of organic polymer or organic composite with photoelectric activity,which can regulate the movement of electrons on the molecular scale,organic photoelectric materials are also called organic semiconductors.Solar cells,transistors,lighting devices,etc.based on organic photoelectric materials have abundant advantages such as fast response,low cost,light weight and easy processing.Therefore,organic optoelectronic materials are one of the most active research fields in modern society.During the continuous development,various research groups have gradually developed a large number of organic small molecular materials,organic polymer materials,and donor-receptor binary materials due to the high research value of the organic photoelectric materials.It mainly contains polymers such as coumarins,polyenes,triphenylamines,and pyridines.The study of the photophysical properties of such organic optoelectronic materials can help researchers to understand the relaxation mechanism of the excited state of organic photoelectric materials better.The research on the charge transfer rate problem can improve the photoelectric conversion efficiency of such materials and and fabricate more efficient photovoltaic devices.In this thesis,the photophysical properties of three organic polymer mateials were studied by using femtosecond pumping detection technology.Firstly,the effect of displacement on the relaxation mechanism of excited compounds was studied.The research objects were polydithiophenyrrolopyrrolodione thiophene and polydithiophenepyrrolopyridinone.Secondly,the ultrafast spectra of three polymers based on the combination of difluoroboron ?-diketone as electron donor and triphenylamine unit as electron acceptor were studied.The main analysis was to discuss the effect of the introduction of vinyl on the ultrafast process of the compounds.Finally,the ultrafast spectra of two polymers composed of ?-diponic acid difluoroborate and terminally linked carbazole units were studied.The effect of solvation on the charge transfer intermediate state of excited compounds was also discussed.Potential applications of compounds in organic light-emitting diodes.The main contents are as follows:1.The optical properties of diketopyrrolopyrrole(DPP)based polymers were studied by time-resolved spectroscopy techniques for the displacement of thiophene units and thieno [3,2-b] thiophene units.Among them,a thiophene unit and a thieno [3,2-b] thiophene unit are used as an electron donor,and DPP is used as a receptor unit.It can be seen from the steady state absorption spectrum,that the role of replacement would lead to blue shift Meanwhile,the transient absorption(TA)data indicate that the role of replacement would not change the relaxation mechanism of polymer but is able to adjust the photo-excitation relaxation rate of polymer.Their intensity-dependent dynamic curves show that the exciton–exciton annihilation(EEA)would participate in the relaxation process when the polymer is in the aggregation.By studying the EEA quenching data of the polymer,we found that the displacement can modulate the spatial distribution of excitons of the excited state compound.The final results will help to understand the relationship between the conjugated unit and the optical properties of the conjugated polymer.2.The nonlinear and linear photophysical properties of the ?–conjugated extension of the complex(ABA,ABVA,AVBVA)formed by the difluoroboron ?–diketone as an electron donor and a triphenylamine unit as electron acceptors were investigated by time-resolved spectroscopy.We mainly discuss the influence of the introduction of vinyl units and solvent polarity on the relaxation mechanism of D-?-A compounds after photoexcitation.The solvent–dependent steady absorption and photoluminescence(PL)spectra data shows that the vinyl unit and the polarity of the solvent influence the photo–physical properties of the compound.Moreover,the vinyl unit would further enhance the role of the polar environment.The transient absorption measurement then offers excitation relaxation behavior.The results show that excited compounds in cyclohexene go back to the ground state through the intramolecular charge transfer(ICT)state,and the transfer lifetime from the initial excited state to the ICT state would prolong after the introduction of vinyl unit.The relaxation behavior becomes complex when cyclohexene is replaced by tetrahydrofuran.Some excited compounds go directly back to the ground state and others go back to the ground state after passing through the ICT state.In addition,two–photon PL measurements and a Z–scan technique are employed to elucidate the role of vinyl units in the nonlinear optical properties of D-?-A compounds.These data help us understand the role of the position and number of vinyl unit units in the photophysical behavior of D-?-A compounds.3.We use ultrafast spectroscopy to study the ultrafast relaxation mechanism of two ?-carbonyl carbonyl ketone complexes of difluoroborate,C2 B and DC2 B.The molecular structure of C2 B is composed of a carbazole unit linked to difluoroboron ?–diketonate directly.DC2 B is composed of two terminal carbazole units directly attached to the difluoroboron ?-diketonate core by vinyl groups.By testing the steady-state data,we found that as the number of donor unit increases,both the steady-state absorption and emission spectra are red-shifted.Although both compounds show two absorption bands,the absorption peak corresponding to the ICT state is more more obviously regulated by the number of donors.At the same time,an increase in the number of donors results in an accelerated rate of fluorescence emission relaxation of the compound.By fitting the TA measurements,it is found that the increase in the number of donors accelerated the rate of ICT,the recombination of the excited states,and the relaxation process from the ICT state to the ground state.Finally,we mixed C2 B and DC2 B and applied them to the white LED test,showing a correlated color temperature(CCT)of 4687 K.The white light emitting diode test results confirmed that C2 B and DC2 B would exhibit a potential application in the organic displaying devices.