Study Of Ultrafast Spectroscopy Of The Conjugated Organic Molecules With ICT Properties

The fluorescencematerials, especially the new kind of organic fluorescence, have many merits like:diversity and easy to adapt. Besides, they have many unique optical properties, such as two photon absorption, two fluorescence emission, solvation, molecular structure changes, aggregation-caused Quenching(ACQ), aggregation induced emission(AIE) and intramolecular charge transfer etc. They attract large attention, and with the study developed, these organic fluorescence materials have been used as fluorescence track materials, nonlinear optical materials and laser materials applied to wide areas including medical science, industry, military and biology field. So it is of significant importance to study the relationship between structure and function as it will help us to produce more potential materials.In this thesis, we used various kinds of optical technologies like steady spectroscopy, Z-scan, time resolved fluorescence and transient spectroscopy(Pump-Probe) to detect some new series organic materials with conjugate structure’s fluorescence and absorption, nonlinear optical properties, two photon absorption and the relaxation of excited states. What’ more, we learned the effects of substituent group, triple bond, linear and multi-branched structure, and the solvent on the optical phenomenon. We believe the information we get from these study have crucial role in exploring the more excellent materials.The works we done are listed below:(1) We studied the steady state spectroscopy and time-resolved spectroscopy of a multi-branched thiophene-based triphenylamine derivatives with triazine core in varied solvents. We found that the solvent have few influence on absorption spectrum, but the fluorescence red ship when the solvent polarity increase. We also notice that the solvent polarity increase the speed of excited state relaxation due to intramolecular charge transfer, and the solvent viscosity can influence the molecular twisted behavior. Meanwhile, the introduction of alkyl chain also result in special properties for its increasing the electron donation ability.(2)We studied the steady state spectroscopy and two photon absorption properties of a kind of salicylideneaniline analogues. The absent of fluorescence when dissolved in pure organic solvent DMF indicate that the molecular rotation or twisted behavior result in increasing of the non-radiative channel. When dissolved in the mixture solvent of water and DMF, the strong fluorescence occur due to the AIE effect, and the two photon absorption cross section increase with the increase quantum yield.(3) We studied the time resolved fluorescence of a kind of linear and multi-branched bithiazole-based derivatives(BZT) dissolved in different solvent. We found that the ICT effect do not happen when dissolved in low polarity solvent. There are lot phenomenon can prove that conclusion:the small Stokes Shift, the single exponential fluorescence decay and the fluorescence lifetime linearly increase with dielectric constant.(4)We also studied the optical nonlinearities of Bi nanospheres suspensions by Z-scan technique in the condition of non-resonant excitation with femtosecond laser, and the third order nonlinear refractive index wasobtained for Bi nanospheres. These samples also exhibit optical limiting ability through the refraction optical limitingdetection. The results indicate that the nonlinear absorptionand scattering can be ignored for the solvent ethanol and theBi nanospheres suspensions present obvious nonlinear refraction properties under the non-resonant femtosecond laserpulse excitation after excluded the nonlinear absorption andnonlinear scattering.