Preparation And Nonlinear Optical Properties Of Novel Porphyrin-based Nanohybrids

Polypyrrole and its derivatives have been extensively studied in bio-medical fields such as protein separation and DNA adsorption,supercapacitors and solar cells because of their low resistance,prospective electrical conductivity and excellent environmentally friendliness.Porphyrins possess an eminent?-conjugated system,which exhibit a stable framwork structure and show an outstanding photo-induced electron-transfer capability,and have drown great attention from analytical chemistry,optical limiting devices and photodynamic therapy areas.Due to its unique electronic structure,graphene exhibits outstanding charge/hole mobility,high Young's modulus and preeminent thermal conductivity.Accordingly,many potential uses in nonlinear optics,high-speed transistor and energy storage can be expected.After graphene is oxidized with concentrated sulfuric acid and concentrated phosphoric acid,a large amount of oxygen-containing organic functional groups such as hydroxyl group,carbonyl group,and carboxyl group appear on the surface of graphene,which endows graphene oxide?GO?to be dispersed in water and other organic solvents in a large amount.Polypyrrole and its derivatives occur to be the new favorite of nonlinear optical?NLO?area due to their extensive?electron delocalization.However,the poor solubility of PPy and its derivatives in water and other organic solvents emerged as the primary hinder for the NLO applications.The functionalization of polypyrrole with soluble molecules?such as phenolic hydroxyl group?has became one of the available methods for solving this problem.The presence of terminal phenolic hydroxyl group on the side of PPy nanohybrids endows PPy a favorable virtue of lipophilicity,and provides a handle for the chemical modification of polypyrrole with porphyrin moieties as well.At the same time,this modified polypyrrole?PPy?could also self-assemble with porphyrins.In addition,the unreacted phenolic hydroxyl groups in PPy-porphyrin composites can also be covalently linked with GO to improve the nonlinearity of these materials.Based on this,three novel NLO functional materials were prepared.Metalloporphyrins(MTpp,M=Zn²⁺,Co²⁺)covalently grafted with the modified polypyrrole nanohybrids were prepared through a covalently functionalized method,andtheresultantsampleswerestudiedwithmicro-Ramanspectrum,Fourier-transforminfrared,thermogravimetricanalysis,X-rayphotoelectron spectroscopy,ultraviolet-visible spectroscopy as well as steady-state and nanosecond time-resolved fluorescence spectroscopic techniques.Steady state fluorescence and nanosecond time-resolved fluorescence spectra suggest effective charge transfer between porphyrin units and PPy.The NLO properties and the optical limiting?OL?performances of the as-synthesized materials were characterized by Z-scan technology at 532 nm with both nanosecond and picosecond laser pulses,the results exhibited that Tpp-Ph-PPy and MTpp-Ph-PPy nanohybrids displayed improved NLO performances compared with those of the constituent PPy or porphyrin moieties due to the synergistic effect of PPy and Tpp.Because porphyrin covalently decorated PPy nanohybrids displayed enhanced NLO properties,we could make sure that porphyrins self-assembled with PPy nanohybrids may exhibit superior NLO performance.On the basis of this,we synthesized 3 kinds of self-assembled nanohybrids?PPy/TPP,PPy/TPP-OH and PPy/TPP?OH?₄?through a self-assembled approach.The resultant PPy/TPP,PPy/TPP-OH and PPy/TPP?OH?₄ nanohybrids were studied with micro-Raman spectrum,Fourier-transform infrared,thermogravimetric analysis,scanning electron microscope,X-rayphotoelectronspectroscopy,fluorescencespectraand ultraviolet-visible spectroscopic techniques.The NLO performances of the resultant PPy/TPP,PPy/TPP-OH and PPy/TPP?OH?₄ nanohybrids are characterized by Z-scan technique at 532 nm with a pulse width of 4 ns,the resultant PPy/TPP,PPy/TPP-OH and PPy/TPP?OH?₄ nanohybrids display improved NLO activities compared to the PPy unit and their corresponded TPP moieties,TPP-OH moieties and TPP?OH?₄moieties,due to the synergistic effect between PPy and porphyrins.MTpp-PPy-GO nanohybrids were prepared through a chemical covalently bonded method,and were characterized by micro-Raman spectrum,Fourier-transform infrared,thermogravimetric analysis,and ultraviolet-visible spectroscopy and steady-state fluorescence spectroscopic techniques.Steady-state fluorescence spectra suggest effective charge transfer between porphyrin units and PPy as well as GO.