سنتز و بررسي پلي آنيلين دهنده - گيرنده با انرژي گافِ نوار پايين

Synthesis and investigation of low band gap energy donor-acceptor polyaniline

در اين كار پژوهشي پليمر با ساختار گروه هاي دهنده-گيرنده حاصل از پلي آنيلين متصل به نانوذرات روي اكسيد (ZnO) در يك انتها و گروه نفتالن در انتهاي ديگر زنجير سنتز، و ساختار و تركيب شيميايي، ريختار محصول و نيز خصوصيات نوري و الكتروشيميايي آن مورد بررسي قرار گرفته است. ساختار شيميايي تركيبات سنتز شده به كمك روش هاي طيف سنجي مادون قرمز تبديل فوريه (Fourier Transform Infrared Spectroscopy, FT-IR)، رزونانس مغناطيسي هسته اي (Nuclear Magntic Resonounce, 1H NMR)، و تركيب درصد اجزاء آلي و معدني آن توسط روش هاي تجزيه وزن سنجي گرمايي (Thermal Gravimetric Analysis, TGA) و طيف سنجي جذب اتمي (AAS)، بصورت 10 درصد بخش معدني و 90 درصد بخش آلي تعيين شده است. ثبت تصاوير ميكروسكوپ الكتروني پويشي (Scanning Electron Microscopy, SEM) نشان داده كه نمونه داراي ذرات با ريختار كروي و اندازه حدود 70 نانومتر مي باشد. طيف سنجي فرا بنفش-مريي بازتابش نفوذي و بررسي رفتار الكتروشيميايي نمونه ها با استفاده از روش ولتامتري چرخه اي (CV) نشان داده كه با اتصال گروه هاي نفتالن و نانوذرات ZnO به دو انتهاي زنجيرهاي پلي آنيلين كاف نوار انرژي نوري و الكتريكي نمونه ها بترتيب به 1/19 و 0/95 الكترون ولت كاهش پيدا كرده است كه به اثر اين گروه ها در افزايش طول سامانه مزدوج، كاهش سطح انرژي پايين ترين اربيتال مولكولي اشغال نشده (LUMO) و افزايش سطح انرژي بالاترين اربيتال مولكولي اشغال شده (HOMO) نسبت داده مي شود. بررسي نمودارهاي CV نشان داده كه اثر اين گروه ها در كاهش سطح انرژي اربيتال LUMO كمي بيشتر از اثر آنها در افزايش سطح انرژي اربيتال HOMO مي باشد.

Research subject: Solar cells has gained a great attention as a green, renewable and cheap energy resources. To overcome the challenging technical problems and improve their competitiveness with silicone solar cells, the design, synthesis and development of new materials with engineered band gap energies has found an undeniable importance. Research approach: Herein, a polymer with donor-acceptor structure based on polyaniline grafted to ZnO nanoparticles at one end and naphthalene moiety at the other end of chains was synthesized , and their chemical structure, composition, morphology, optical and electrochemical properties were investigated. The chemical structure of the materials were analyzed by FT-IR and 1H NMR spectroscopies. The organic and inorganic contents of materials were determined by thermal gravimetric analysis (TGA) and atomic absorption spectroscopy (AAS) techniques. The morphology and size of nanoparticles were observed by scanning electron microscopy (SEM). The optical and electrical band gap energy of the samples were measured by ultraviolet visible-diffuse reflectance (UV-Vis-DRS) spectroscopy and cyclic voltammetry (CV) diagrams. Main results: The chemical structure of designed materials was successfully confirmed by the results of FT-IR and 1H NMR spectra. TGA and AAS analysis indicated that the synthesized final material is contained about 10% of ZnO and 90% of organic parts including toluene-2,4-diisocyanate, 2,4-diaminotoluene, polyaniline and naphthalene groups. An almost highly uniform spherical nanoparticles with sizes about 70 nm were observed by SEM images. UV-Vis-DRS spectroscopy and CV diagrams revealed that by grafting ZnO nanoparticles and naphthalene moiety to the polyaniline chain ends, the optical and electrical band gap energy of the sample are lowered to 1.19 and 0.95 eV, respectively. It was concluded that the grafted groups to chain ends increase the length of conjugated system, lowering the energy level of lowest unoccupied molecular orbital (LUMO) and increasing the energy level of highest occupied molecular orbital (HOMO). Detailed analysis of CV diagrams indicated that the effect in lowering of LUMO has been a bit more pronounced than the increasing of HOMO energy level.