The Preparation And Nonlinear Optical Properties Of Phthalocyanine/Polyoxometalates Self-Assembly Films

In this thesis, two series of composite films with alternating layers (PAH/PSS)3(AB/POM)n (1) and (PAH/PSS/PAH)(POM/CuPTAs)n (2)(PAH-polyallylamine hydrochloride; PSS-polystyrene sulfonate; POM=SiW12, PW12, PM012, PMo10V2) containing Alcian Blue-tetrakes (methyl-pyridinium) chloride (AB, water-soluble) or/and Copper (II)4,9,16,23-phthalocyanine tetraamines (CuPTAs, soluble in DMF) and Keggin type polyoxometalates were fabricated by electrostatic self-assembled layer-by-layer (LBL) technique. The series of composite films were characterized by UV-vis, FT-IR spectra and X-ray photoelectron spectroscopy (XPS). The results indicated that phthalocyanines (AB, CuPTAs) and POMs were constantly incorporated in the multilayers with uniform deposition. More importantly, the nonlinear optical properties of the phthalocyanine-POMs composite films were studied by Z-scan technique and the results were described as follows: (1) The series of phthalocyanine-POMs composite films1and2exhibited self-defocusing behavior and saturable absorption effect with nanosecond laser, while the corresponding pure phthalocyanine solution (AB in water, CuPTAs in DMF) possessed reverse saturable absorption. Moreover, the nonlinear optical absorption coefficient β(m/W) and refractive index n2(m2/W) of films were4-5orders larger than those of pure phthalocyanine solution. The above facts indicated that fabricating phthalocyanines into films was a good method to remarkably modify and enhance the third-order nonlinear optics. On the other hand, the third-order NLO susceptibilities x(3) of films1and2incorporated with POMs were larger than those of pure phthalocyanine films ((AB/POM),,,(POM/CuPTAs)n). The calculated x(3) values are in following order:x(3)(Phthalocyanine/PSS)<x(3)(Phthalocyanine/SiW,2)<%(3)(Phthalocyanine/PW12)<%(3)(Phthalocyanine/PMo12)<x(3)(Phthalocyanine/PMO10V2)(Phthalocyanine=AB, CuPTAs), confirming that the combination of Keggin type POMs with phthalocyanine in multilayers was an excellent approach to improve the NLO responses of phthalocyanine films.(2) HOMO-LUMO orbital levels of phthalocyanine and POMs were calculated by cyclic voltammetry (CV) spectra. The lower LUMO level of POM than the phthalocyanine indicated the easy transformation of excited electron from AB/CuPTAs to the POM when exposed in laser, which was thought to be responsible for the donor-acceptor system (phthalocyanine molecules acted as electron donor while POMs as electron acceptor) formed in films1and2. In addition, it was noted that the LUMO energy levels were in following order:ELVMo (Phthalocyanine)>LLUMO (SiW,2)>EL?UMO (PW12)> ELUMO (PMo12)>ELUMO (PMo10V2),while the third-order NLO susceptibility x(3) values were as follows:x(3)(Phthalocyanine/SiW12)</(3)(Phthalocyanine/PW12)<x(3)(Phthalocyanine/PMo12)<x(3)(Phthalocyanine/PMo10V2).This observation might imply that discrepancy of LUMO levels between phthalocyanine and POM was proportional to the third-order NLO responses.(3) We also checked the effects of different numbers of layers on the NLO properties of the composite films1and2. Investigations revealed that with the increasing number of layers (the thickness of films increased), the third-order nonlinear absorption and refractive effects also improved, which inspired us the NLO responses could be modified by fine tuning the thickness of composite films to meet the demands of different devices.(4) Finally, we examined the third-order NLO absorption coefficient β and refractive index n2of films1and2under different energies. The results showed that with the increasing laser energies, the absolute values of n2of1and2as well as β values of2decreased gradually, which related with the saturable absorption effect (derived from the electron transfer process between phthalocyanine and POMs)in phthalocyanine/POMs composite films.