| Laser photosensitive nonlinear optical(NLO)materials have drawn increasing attention with the rapid development of laser technology and its extensive applications in scientific and social communities such as mode-locking,material diagnosis,biomedicine,and micromachining.However,due to difficulties in quantity production and limited application ranges,there are very few NLO functional materials that have been yet practically applied in real world.Therefore,the design and development of photosensitive functional NLO materials that can be used across a wide range of laser irradiation in chemical ways are currently becoming one of the hottest research topics in world’s optical functional materials research.Due to the unique structural characteristics,the common carbon-based materials,graphene and carbon nanotubes have been proven to be easily modified and reported to have great optical limiting properties;owing to the highly conjugated electron delocalization properties,porphyrin monomers are often used as antenna compounds to functionalize carbon-based materials for building a lot of organic-inorganic functional nanohybrid materials,of which the NLO properties are enhanced through the synergistic effect between their two components.By exploring the advantages and disadvantages of these organic-inorganic functional nonlinear nanohybrid materials,this paper proposes different chemical ways to assemble several porphyrin monomers and porphyrin oligomers onto single-walled carbon nanotubes(SWCNT)or graphene for NLO applications under different wavelengths and different laser pulse conditions.By constructing in-depth studies on the NLO properties of these resultant functional nanohybrid materials,the structure-property relationship,especially the influence of photoinduced intrasystem electron/charge transfer on NLO performance has been explored and the strategies for constructing better functional NLO materials have been summarized.In the second chapter,a pyrazine-linked porphyrin dimer-functionalized graphene nanocomposite was successfully constructed by physical grafting onto the surface of graphene through π-π stacking.Z-scan studies demonstrate that an unprecedented enhancement of reverse saturable absorption(RSA)of porphyrin dimer than that of porphyrin monomer is observed under nanosecond laser irradiation,which can be ascribed to its large π-conjugated system,a longer excited-state lifetime in ns scale,and reorganized excited states.The nanocomposite exhibits the strongest nonlinear optical(NLO)absorption properties under identical laser conditions when compared to its individual precursors,stemming from a synergistic effect of the strongly enhanced RSA of porphyrin dimer,the nonlinear scattering of graphene and effective photoinduced electron/energy transfer from porphyrin dimer to graphene.These results expand the applications of porphyrin dimers in developing novel NLO-active materials towards ns laser irradiation and reveal that G-di TPP is a very promising optical limiter candidate.To gain further insight into the optimization of NLO properties in the femtosecond regimes,Chapter 3 mainly describes the preparation of a conjugated triply-fused porphyrin dimer tape.This compound is typically synthesized through the oxidative dehydrogenation of porphyrin monomers with one unsubstituted meso position,which affords three new C-C bonds between the two adjacent porphyrin monomers and a highly conjugated system.This tape has one acetylaniline group and one aniline group at each of the two terminal meso positions.Through the Z-scan technique,this porphyrin dimer was found with an obvious two-photon absorption(TPA)at 800 nm under femtosecond laser irradiation and a large TPA cross-section value about13200 GM.Based on Chapters 2 and 3,the main content of Chapter 4 is the preparation and applications of triple-fused porphyrin dimer functionalized SWCNT nanohybrid,which is formed by triple-fused porphyrin dimer covalently linking to the surface of SWCNT through free radical addition reaction,rather than simply mixing porphyrin dimers with SWCNT in physically blending way.In sharp contrast to SWCNT and porphyrin monomer and the porphyrin monomer-SWCNT nanohybrid,this novel nanohybrid has a wide window(600-850nm),approaching the NIR region(1100 nm),and displays strong RSA under femtosecond laser irradiation.To the best of our knowledge,such a strong OL effect under fs-laser radiation has not been realized in carbon-based nanohybrids reported to date,and the absorption switch from SA to RSA is unprecedented and observed for the first time in porphyrin-functionalized carbonbased NLO materials,which provides a new paradigm to the development of versatile NLO materials and devices.In addition,enhanced OL of this novel nanohybrid is seen at 532 nm,in comparison with that of the porphyrin monomer-SWCNT nanohybrid,a benchmark for carbonbased NLO materials in recent years in the ns regime.Under fs irradiation,this nanohybrid also exhibits a particularly strong OL effect with 1064 nm pulses.Based on these results,this novel nanohybrid has been proven to be a very promising optical limiter candidate material,not only under diverse length laser pulses(ns and fs regimes)but also with a wide range of wavelengths(i.e.532,800,1064 nm).The contents of Chapters 5-7 focus on exploring the influence of modification methods on the third-order nonlinear properties of porphyrin monomers functionalized carbon-based materials.Among them,Chapter 5 describes the preparation of a nanohybrid obtained by porphyrin monomers axially coordinated with reduced graphene oxide(RGO)using a two-step method and the NLO performance of this resultant nanohybrid under 532 nm,nanosecond pulsed laser was compared with the traditional nanohybrid prepared diazonium reaction.The experimental results demonstrate that the nonlinear optical properties of the obtained nanohybrid material in this two-step way are significantly stronger than that of the traditional nanohybrid by diazonium radical addition under identical conditions,which changes the fact that the NLO performance in covalently-linked porphyrin-carbon nanohybrid is always better than that in nanohybrid obtained through coordination ways.In Chapter 6,a new approach to functionalizing GO with meso-substituted formylporphyrins at GO’s edge sites via imidazole condensation is developed,which affords a novel nanohybrid covalently linked by imidazole rings between two components.The redshifted steady-state absorption,largely quenched fluorescence,and strongly enhanced nonlinear optical properties through Z-scan studies at quite lower input energies demonstrate that this nanohybrid exhibits a more effective photoinduced energy/electron transfer between the intrahybrid two components and can be flexibly applied as an optical limiter candidate.The content of Chapter 7 further exploits the edge-functionalization method on the basis of Chapter 6.In this work,an fs-active nanohybrid was obtained by fusing porphyrin monomers onto graphene oxide(GO)at the edge sites.Through this edge fusion method,porphyrin monomers with two adjacent amino groups were reacted with ortho-quinones at the edge of GO,forming pyrazine rings which make porphyrin monomers approximately in the same plane with GO.The nanohybrid material prepared by this method is different from the traditional nanohybrids due to that the chromophores in the latter nanohybrids are often perpendicular to the surface of graphene.By studying the steady-state photophysical properties of this nanohybrid,it is found that there is a significant electron and energy transfer between porphyrin and GO.By exploring its Z-scan curve,it is found that its NLO absorption is much different from that of the traditional nanohybrids.Its enhanced nonlinear optical properties in the femtosecond regimes are mainly attributed to the strong electron-coupling effect between GO and porphyrins.These results show that the NLO applications of the chromophores’ functionalized carbon-based nanohybrid materials can be largely optimized by changing the linking ways between two components. |
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