| In this thesis, I investigated the linear and nonlinear optic properties of pophyrin. Fluorescence spectra have been used to analyze structure,group of porphyrin molecules and their solutions etc. By varing the structure,group and solution of porphyrin, one can obtain different optical characterastics, and get a critical value of optical limiting we wanted.Porphyrins are well-known conjugate tetrapyrrolic macrocycle compounds. As a kind of special macrocyclic compounds with the particular structure and the nature, porphyrin derivatives have received more and more attention from many investigators in various fields, such as, biological chemistry, medical chemistry,photophysics, photochemistry and material science etc.In material science, porphyrin and its derivatives with special electronic structure are excellent organic semiconductor materials and they have received considerable attention in recent years. Porphyrin derivatives as photosensitizer have been wildly used in photodynamic therapy of cancer and cardiovascular diseases. We have investgated the nonlinear and linear optical properties of five porphyrin derivatives, those are one monomer and four dimers. Their molecule configurations are shown in the follow Figs.The UV-absorption and fluorescence spectra were obtained at room temperature with concentrations at about 1×10-4mol /L in DMF.All UV-Vis spectra of the porphyrins show a typical set of Soret bands and the Q-bands in the visible region. The band around 420nm is assigned to the Soret band which arises from the transition of , and the other four absorption maxima around 516,550,590 and 645nm are attributed to the Q-bands corresponding to the transition of。Similar results were obtained for the porphyin dimer and monomer(H2CPTPP) in the UV-visible absorption spectrum. It indicates that the inter-porphyrin electronic interactions mediated by the linker group do not significantly affect the electronic properties of the porphyrinπ-conjugated system.The fluorescence spectra of the monomer and dimer are different. Upon excitation of the above solutions at 420nm, the Q band emissions show two bands at 650nm and 710nm. The two bands are assigned to the S1-S0 transition and correspond to the Q(0-0) and the Q(0-1) bands of the porphyrin emission. The dimer d has a stronger fluorescence than the others, because it maybe has a face-to-face construction. This construction enhanced the ability of electrons transfer between the two s1 orbit of monomer. Dimer a,b and c show a weak fluorescence peak which attribute to their distortion configuration of two dimer. Distortion reduce the energy of two electronic orbit and show a red shift of several nanometer. The change of porphyrin structure can cause the radiation transition of electrons on the porphyrin skeleton from the excited state to the ground state to be more difficult.Now, we reviewed the fluorescence of different concentration solution. Porphyrin fluorescence emission peak will descend in high concentration due to deactivation and fluorescence quenching by collision in polar DMF solution. When porphyrin transition fromπtoπ*, polar solution effect the porphyrin excitated state and reduce its energy. So the emission wavelength will have a red shift.Last we investigated the solution nonlinear optic absorption. The nonlinear optical effects of porphyrin have been investigated with the CW laser lines of 532 nm. there is a thermal self-defocusing effect.These curves of transmittance show a decrease with the increase in the incident laser power, which means that the sample has reverse saturated absorption property under the the laser wavelengths. It's well known that both thermal self-defocusing effect and reverse saturated absorption can lead to optical limiting. It was found that porphyrin has good optical limiting property, and that the threshold values of optical limiting are different as shown in the following Figs.Our results give us hints that porphyrins are new optical limiting materials with a great potential application value.
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