| In the field of science and technology and in our daily life LASER has been applied in many fields which bring a great approach according to modern aspects,as a result,traditional linear materials have been replace by nonlinear optical ones which are of growing interest in modern research.Due to their great potentials which are used in many fields as photonic devices,such as optical data storage,optical limiting,telecommunications,signal processing,optical phase conjugation,and so on.In photonics technology,photon has replaced the electron because they travel much faster than electron and broadcast information without electric and magnetic field interference.In this perspective,nonlinear optical material especially third-order nonlinear optical materials have become promising material.At the start,inorganic materials were used for third-order optical nonlinearity,later these materials were replaced by organic materials due to delocalization of ? electrons which are responsible to enhance the third-order nonlinear optical properties.In this quest,porphyrins and phthalocyanines due to highly delocalized 18? electronic system or more were on the flagship positions but these materials also have some limitations.To overcome these limitations these materials have been modified greatly to meet the demand of modern science and technology requirement.To enhance the third-order nonlinear response,vast variety of inorganic materials have been grafted on porphyrins or phthalocyanines electrostatically or covalently.Among the inorganic materials,polyoxometalates(POM)are best candidates for the grafting on the porphyrins and to tune the third-order nonlinear response.In order to deeply study in the field of third-order nonlinear optical material,we have selected this promising yet inadequately explored area in the field of third-order nonlinear optics.This work is composed of four chapters but mainly composed of major three projects.Chapter 1 is the introduction part of the dissertation which explain the importance and the applications of this field.Chapter 2:Four new organic-inorganic hybrids,[N(C4H9)4]5H-[{HNC2O(CH2O)3P2V3W15O59}C44N4H29O3](TPPOH-1POM),[N(C4H9)4]10H2[{HNC2O(CH2O)3P2V3W]5O59}2C44N4H28O2](TPPOH-2POM trans),[N(C4H9)4]10H2[{HNC2O(CH2O)3P2V3W15O59}2C44N4H28O2](TPPOH-2POM cis),and[N(C4H9)4]15H3[{HNC2O(CH2O)3P2W15V3059}3C44N4H270](TPPOH-3POM),have been synthesized by covalently grafting the Dawson-type polyoxometalate(POM)[N(C4H9)4]5[H4P2W15V3O62]onto new porphyrins N-[1,3-dihydroxy-2-(hydroxymethyl)propan-2-yl]-4-[10,15,20-tris(4-hydroxyphenyl)porphyrin-5-yl]benzamide(TPPOH-1Tris),4,4'-[5,15-bis(4-hydroxyphenyl)porphyrin-10,20-diyl]bis[N-[1,3-dihydroxy-2-(hydroxymethyl)propan-2-yl]benzamide](TPPOH-2Tris trans),4,4'-[10,15-bis(4-hydroxyphenyl)porphyrin-5,20-diyl]bis-[N-[l,3-dihydroxy-2-(hydroxymethyl)propan-2-yl]benzamide](TPPOH-2Tris cis).and 4,4',4"-[20-(4-hydroxyphenyl)-porphyrin-5,10,15-triyl]tris[N-[1,3-dihydroxy-2-(hydroxymethyl)propan-2-yl]benzamide](TPPOH-3Tris),respectively,in N,N-dimethylacetamide under nitrogen.The hybrid compounds were thoroughly characterized by elemental analysis,FT-IR,NMR(1H,2D NOESY,31P,and 51V),ESI-MS,MALDI-TOF-MS,UV-vis,and fluorescence spectroscopy.All porphyrins and their corresponding hybrids exhibited remarkable third-order nonlinear-optical responses under laser irradiation,with the intensity of light at focus E0 being 4.2 ?J at wavelength 532 nm,pulse duration ??6 ns,and repetition rate 10 Hz.The molecular second hyperpolarizability(y)values of the hybrids(TPPOH-1POM,TPPOH-2POM trans,TPPOH-2POM cis,TPPOH-3POM)were calculated to be 8.48×10-28 esu,8.94×10-28 esu,10.16×10-28 esu,and 8.93×10-28 esu,while the molecular second hyperpolarizability(y)of their corresponding porphyrin precursors(TPPOH-1Tris,TPPOH-2Tris trans,TPPOH-2Tris cis,and TPPOH-3Tris)were 7.19×10-28 esu,8.09×10-28 esu,9.07×10-28 esu,and 7.24×10-28 esu,respectively.The ? values of the cis forms were found to be superior to those of all other compounds,indicating the significant role of the greater dipole moment and low symmetry of the cis form compared to other compounds.It was also found that the fluorescence intensity was decreased by 81.52%,90.37%,93.93%,and 84.62%for the hybrids TPPOH-lPOM,TPPOH-2POM trans,TPPOH-2POM cis,and TPPOH-3POM with respect to their corresponding precursors,respectively,which reveals the Dawson-type POM as a strong quencher.This quenching phenomenon not only indicates again unequivocally the formation of hybrid compounds but also may imply a photoinduced electron/energy-transfer process favored from a porphyrin moiety to a Dawson-type POM moiety.Chapter 3:To investigate the third-order nonlinear optical properties by grafting the different types of polyoxometalates on the different porphyrins,four new covalently bonded porphyrin-polyoxometalates hybrids[N(C4H9)4]2[C44H2903N4(NHC2O)(OCH2)3(V6O13)(OCH2)3(C20NH)N403H29C44](TPPOH@1Lindqvist),[N(C4H9)4]4[C44H28O2N4(NHC2O)2(OCH2)6(V6O13)2(OCH2)6(C2ONH)2N402H28C44](TPPOH@2Lindqvist),[N(C4H9)4]3[C44H2903N4(NHC2O)(OCH2)3(MnMo6O18)(OCH2)3(C2ONH)N403H29C44](TPPOH@1 Anderson),and[N(C4H9)4]6[C44H28O2N4(NHC2O)2(OCH2)6(MnMo6O18)2(OCH2)6(C2ONH)2N402H28 C44](TPPOH@2Anderson)have been synthesized by integrating the Lindqvist and Anderson type polyoxometalates onto the porphyrins derivatives N-[1,3-dihydroxy-2-(hydroxymethyl)propan-2-yl]-4-[10,15,20-tris(4-hydroxyphenyl)porphyrin-5-yl]benzamide(TPPOH@1Tris)and 4,4'-[10,15-bis(4-hydroxyphenyl)porphyrin-5,20-diyl]bis-[N-[1,3-dihydroxy-2-(hydroxymethyl)propan-2-yl]benzamide](TPPOH@2Tris).These hybrids were systematically characterized by FT-IR,elemental analysis,1H NMR,ESI-MS,UV-vis spectroscopy,and fluorescence emission spectroscopy.The efficiency and effectiveness of these proposed hybrids have been examined where porphyrins as electron donors and polyoxometalates(Lindqvist and Anderson)as electron acceptors are connected covalently each other through tris group.Third-order nonlinear optical properties of all the hybrids and their porphyrin precursors(TPPOH@1Tris,TPPOH@2Tris)were studied by using the Nd:YAG laser,the intensity of light 4.2 ?J at focus E0,wavelength 532 nm,pulse duration ??6 ns,and repetition rate 10 Hz.The molecular second hyperpolarizability(y)of the hybrids TPPOH@1Lindqvist,TPPOH@2Lindqvist,TPPOH@1Anderson,and TPPOH@2Anderson is calculated to be 8.294×10-28 esu,9.409×10-28 esu,8.363×10-28 esu,and 9.696×10-28 esu while the molecular second hyperpolarizability(y)of the porphyrin precursors TPPOH@1Tris,TPPOH@2Tris,is 7.192×10-28 esu,and 9.069×10-28 esu,respectively.It is found that there is a remarkable enhancement in the molecular second hyperpolarizability(y)of hybrids than their porphyrin precursors.It is also found that the fluorescence intensity was decreased as 98%,97%,93%,and 89%for the hybrids with respect to their porphyrin precursors respectively.This quenching phenomenon was the indication of the formation of the hybrids along the photoinduced electron/energy transfer process from porphyrin moiety to polyoxometalate(POM)cluster.Chapter 4:In order to justify/evaluate the effect of different types of interactions between POM and porphyrins on the nonlinear optical properties of their resulting systems,the third-order nonlinear optical properties of the covalently bonded Dawson POM-porphyrin hybrids having one,two and three Dawson POM(s)and also electrostatically bonded compound "Hybrid Compound 1”which is composed of Dawson POM and porphyrin with 1:1 ratio and the physical mixture of H2THPP and Well-Dawson POM with different ratio like 1:2 and 1:3 as archetypal systems were examined.These systems under laser irradiation,with the intensity of light 4.2 ?J at focus E0 at wavelength 532 nm,repetition rate 10 Hz,and.pulse duration ??6 ns exhibit remarkable third-order nonlinear optical properties.The molecular second hyperpolarizability(y)of covalently linked porphyrin-POM hybrid compounds having one,two and three POMs with one porphyrin are 8.48 × 10-28 esu,10.16 × 10-28 esu,and 8.93 × 10-28 esu which are higher than electrostatically bonding hybrid and physical mixture in ratio 1:2,1:3 of porphyrin and POM are 4.7238× 10-28 esu,2.4248× 10-28 esu,2.2302× 10-28 esu,respectively.From the results it is clear that covalently bonded hybrids are superior to electrostatically bonded hybrid,electrostatically bonded hybrid has higher value than physical mixture.In physical mixture of porphyrin and POM,the molecular second hyperpolarizability(y)of these solutions decreased as concentration of POM molecules increases. |
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