Fabrication,Characterization And Nonlinear Optical Properties Of Porphyrin-Polyoxometalate Hybrid Materials

Molecular compounds having nonlinear optical(NLO)properties are significantly important due to vast range of applications in variety of optoelectronic devices that are being used widely in fields of signal processing,telecommunications,optical switches,photonic devices,optical phase conjugation,laser protection,information storage and so on.Photonics technology uses a photon as an alternative to electron because it travels much faster than electron,to obtain,accumulate,process and broadcast information without electrical or magnetic interference.The nonlinear optical field is very broad and had begun in early 1960's with the advent of laser but the third order aspects of NLO materials have been developed recently in several decades.In the quest of third order NLO materials,porphyrins and phthalocyanines found to be flagship position but the limitations associated with these materials compelled researchers to substitute or modify them with other materials in order to fetch the demands of modern technology requirements.A vast variety of inorganic martials have been grafted with porphyrins both covalently and noncovalently to enhance/tune the third order nonlinear response of porphyrins.Among them,POM(polyoxometalate),a class of M-O clusters,is founds to be best combination of NLO hybrid materials with porphyrins.In order to further look deep insight into these materials,we selected this unexplored area of research to contribute our efforts for NLO.This work is mainly composed of three major projects.Chapter 1 covers the introduction part of my dissertation while research projects are subdivided into three more chapters.Each of the chapters,contains fundamental concept with the background introduction,experimental work,characterization techniques,results and discussion with conclusion.Chapter 2:The electrostatic interaction of tris(alkoxo)ligand functionalized Anderson-type polyoxometalate(POM for short)anions[XMo6O18?(OCH2)3CNH2?2]3-(where X = Mn or Fe)having ?-type structures and[H2ZnMo6O18?(OCH2)3CNH2?2]2_having ?-type structure with porphyrin based cation[H2TPP]2+ results in formation of three supramolecular compounds[H2TPP]1.5[MnMo6O18?(OCH2)3CNH2?2](1),[H2TPP]1.5[FeMo6O18{(OCH2)3CNH2 }2]· 2C3H7NO(2)and[H2TPP][H2ZnMo6O18{(OCH2)3CNH2}2]·2(C2H5)2O(3),which were systematically characterized by means of elemental analyses,FT-IR,UV-vis.,electron spray ionization mass spectra.The third order nonlinear optical properties were studied by a Z-scan measurement using Nd:YAG laser at 532 nm with a pulse duration of ? = 6 ns and the results showed that all the supramolecular compounds have significant nonlinear reverse saturated absorption(RSA)and self-defocusing behaviour especially the compound 3 has noteworthy improvement of second hyperpolarizability y value(1.35× 1 0-27 esu)compared to parent porphyrin(7.7×1 0-28 esu).Fluorescence is quenched by ca.74%in compound 3,37%in compound 1 and 30%in compound 2 compared to that of parent porphyrin and the order is(3)>(1)>(2),respectively,indicating different quenching effect of the different POM anions.Parallelly,it was found that the three POM anions have different onset reduction potentials due to different central metal atom and overall cluster structure,corresponding to different HOMO-LUMO gaps(Eg)of the resulting supramolecular compounds with Eg(3)<Eg(1)<Eg(2)<Eg(parent porphyrin).Thus,we thought that the easier electronic charge transfer from porphyrin to POM anions by irradiation with laser light play a key role in the enhancement of nonlinear optical response in supramolecular compounds.Chapter 3:Porphyrin-POM hybrids are a unique class of NLO materials with promising properties.Thus,in order to understand the inherent structure activity relationship and deep insight into the understanding of intrinsic NLO property in Porphyrin-POM hybrids,two covalently linked hybrid compounds with molecular formulas[(C4H9)4N]2[V6013?(OCH3)3CNHC(O)-C44H29N4?2](1)and[(C4H9)4N]2[V6O13?(OCH3)3CNHC(0)-C44H27N4Zn?2](2)have been fabricated and systematically analyzed by FT-IR,ESI-MS and !H-NMR.The Z-scan measurement,conducted by irradiation at ? = 532 nm with the 6 ns duration at focus E0 = 4.2 ?J,revealed that both the hybrid compounds have reverse saturation absorption as well as self-defocusing performance,particularly compound 1 has shown enhancement y value(9.24×10-28 esu)assessed to C49H39N5O4(denoted as L-1,7.48×10-28 esu)while the compound 2 has shown noteworthy reduction of ? value(2.70×10-28 esu)compared to C49H37N5O4Zn(denoted as L-2,4.71 ×10-28 esu).Thus,concluding that the NLO response could be modulated by removal of central metal atom from porphyrin and/or fine structural modification in porphyrin-POM hybrid system.Chapter 4:In order to understand the influence of different electron donor groups(4-Hydroxyphenyl,4-Pyridyl and 3,4-Dimethoxyphenyl)in symmetric porphyrins of resulting supramolecular compounds containing Keggin-type[PMo10V2O40]5-anion which is found to be an excellent electron acceptor due to its fascinating properties,we synthesized electrostatically bonded supramolecular hybrids.The interaction of POM anion with symmetric porphyrins results in formation of disalts with molecular formulae[C44H32N4O4][H4PMo10V2O40]2(1),[C40H28N8][H4PMo10V2O40]2(2)and[C52H48N4O8][H4PMo10V2O40]2(3)in 2:1 by accepting protons from polyoxometalate and systematically characterized.The Z-scan measurement,conducted by irradiation at? = 532 nm with the 6 ns duration at focus E0 = 4.2 ?J,revealed that the hybrids have reverse saturation absorption with enhancement of second hyperpolarizability y value in following order:?(2)<?(1)<y(3)which is parallel to the charge transfer ability of parent porphyrins i.e;(6)>(4)>(5).The Z-scan measurement results also revealed that greater the electron donor ability of functional groups on the porphyrin,greater would be the NLO response which could be altered by minor changing in the structure of porphyrin-POM containing supramolecular compounds.