Covalent edge-functionalization of graphene oxide with porphyrins for highly efficient photoinduced electron/energy transfer and enhanced nonlinear optical performance

Covalent modification of graphene oxide(GO)with functional chromophores plays an important role in constructing various kinds of advanced optoelectronic materials for applications in molecular diagnosis,light-harvesting,photodynamic therapy,and optical limiting.Herein,a new approach to functionalizing GO with meso-substituted formylporphyrins at GO’s edge sites via imidazole condensation is developed,which affords a novel GO-imi-Por nanohybrid covalently-linked by imidazole rings between two components.The structure of the GO-imi-Por nanohybrid was thoroughly characterized by scanning electron microscopy(SEM),attenuated total reflectance-Fourier transform infrared(ATR-FTIR),Raman,and X-ray photoelectron spectroscopy(XPS).The red-shifted steady-state absorption,95%quenched fluorescence,and largely enhanced nonlinear optical(NLO)properties through Z-scan studies at lower input energies demonstrate that this GO-imi-Por nanohybrid exhibits a more effective photoinduced energy/electron transfer between the intrahybrid two components and can be flexibly applied as an optical limiter candidate.This covalent edge-functionalization approach provides a new paradigm for constructing various edge-expanding GO nanohybrids with an efficient energy/electron transfer process and improved nonlinear optical effects,which would draw inspiration for engineering more adaptable optoelectronic devices.

A 1,3-dipolar cycloaddition protocol to porphyrin- functionalized reduced graphene oxide with a push-pull motif

Reduced graphene oxide （RGO） has been covalently functionalized with porphyrin moieties by two methods： A straightforward Prato reaction （i.e. a 1,3-dipolar cycloaddition） with sarcosine and a formyl-containing porphyrin, and a stepwise method that involves a 1,3-dipolar cycloaddition to the RGO surface using 4-hydroxybenzaldehyde, followed by nucleophilic substitution with an appropriate porphyrin. The chemical bonding of porphyrins to the RGO surface has been confirmed by ultraviolet/visible absorption, fluorescence, Fourier-transform infrared, and Raman spectroscopies, X-ray powder diffraction and X-ray photoelectron specfroscop）~ transmission electron and atomic force microscopy, and thermogravimetric analysis; this chemical attachment assures efficient electron/energy transfer between RGO and the porphyrin, and affords improved optical nonlinearities compared to those of the RGO precursor and the pristine porphyrin.

Multi-walled carbon nanotubes covalently functionalized by axially coordinated metal-porphyrins： Facile syntheses and temporally dependent optical performance

Axially coordinated metal-porphyrin-functionalized multi-walled carbon nanotube （MWCNT） nanohybrids were prepared via two different synthetic approaches （a one-pot 1,3-dipolar cycloaddition reaction and a stepwise approach that involved 1,3-dipolar cycloaddition followed by nucleophilic substitution）, and characterized through spectroscopic techniques. Attachment of the tin porphyrins to the surface of the MWCNTs significantly improves their solubility and ease of processing. These axially coordinated （5,10,15,20-tetraphenylporphyrinato）tin（Ⅳ） （SnTPP）- MWCNTs exhibit significant fluorescence quenching. The third-order nonlinear optical properties of the resultant nanohybrids were studied by using the Z-scan technique at 532 nm with both nanosecond and picosecond laser pulses. The results show that the nanohybrids exhibit significant reverse saturable absorption or saturable absorption when nanosecond or picosecond pulses, respectively, are employed. Improvement in the nanosecond regime nonlinear absorption is observed on proceeding to the nanohybrids and is ascribed to a combination of the outstanding properties of MWCNTs and the chemically attached metal-porphyrins.

Molybdenum Phosphide Flakes Catalyze Hydrogen Generation in Acidic and Basic Solutions

Molybdenum phosphide (MoP) flakes were synthesized by the reduction of hexaammonium heptamolybdate tetrahydrate and ammonium dihydrogen phosphate. The flakes are porous and constructed by MoP nanoparticles with ca. 100 nm diameters. The lateral size of flakes ranges from less than 1 μm to larger than 5 μm, and the thickness of MoP fakes is ca. 200 nm. The mixture of MoP flakes and carbon black exhibits effective catalytic activity in the hydrogen evolution reaction. The optimal overpotential required for 20 mA·cm﹣2 current density is 155 mV in acidic solution and 184 mV in basic solution. The mixture can work stably in long-term hydrogen generation in both acidic and basic solution. The faradaic yield of mixture in hydrogen evolution reaction is nearly 100% in both acidic and basic solution. The Mo and P species in MoP flakes are found to have small positive and negative charge, respectively. The catalytic activity of MoP flakes is likely to be correlated with this charged nature.

Syntheses, Structures and Properties of 3d-4f Heterometallic Coordination Polymers Based on Tetradentate Metalloligand and Lanthanoid Ions

Based on tetradentate metalloligand LCu ([Cu(2,4-pydca)2], 2,4-pydca = pyridine-2,4-dicarboxylate) and lanthanides (Sm3+, Dy3+), two 3d-4fheterometalliccoordination polymers, namely, {[Sm2 (DMSO)4 (CH3OH) 2][LCu]3·7DMSO·2CH3OH}n 1 and {[Dy2 (DMSO)3 (CH3OH)][LCu3 (DMSO)]·4DMSO·CH3OH}n 2 (DMSO = dimethyl sulfoxide), have been synthesized and well characterized by elemental analysis, Fourier-transform infrared spectroscopy, thermogravimetric and single-crystal X-ray diffraction analysis. Single-crystal X-ray analysis reveals that both 1 and 2 crystallize in the triclinic crystal system with P-1 space group and possess the 3D framework structures, which are constructed from metalloligands LCu connecting with {Sm2} and {Dy2} clusters, respectively. The 3D structure of 1 has a 6-connected single-nodal topology with the point symbol {49 × 66}, while 2 features a different framework with the point symbol of {412 × 63}. Thermogravimetric analysis exhibits that the skeleton of both 1 and 2 collapse after 350℃. Magnetic properties of 1 and 2 have also been investigated.

One-Step Seedless and Catalyst—Free Growth of Hierarchical ZnO Film Promising for Photoelectrochemical Application

A facile one-step method was developed for the fabrication of hierarchical ZnO film on substrate. Neither seed nor catalyst layer is necessary for the growth of hierarchical ZnO film. Three kinds of nucleation process were found, and the influences of growth time, growth electrolyte, growth temperature on the morphology of ZnO film were evaluated. Hierarchical ZnO film can absorb more than 97% of incident photons with wavelength shorter than 380 nm. Such hierarchical ZnO film would be a promising scaffold for photoelectrochemical application.

Cascading electron transfer and photophysics in a donor-π-acceptor graphene nanoconjugate

Electron-donating porphyrins(Por),electron-accepting phthalocyanines(Pcs),and reduced graphene oxide(RGO)were integrated into a multicomponent nanoconjugate(Por-RGO-Pc).The donor-π-acceptor nanoconjugate Por-RGO-Pc was characterized using Fourier transform infrared spectroscopy(FTIR),transmission electron microscopy(TEM),scanning electron microscopy(SEM),atomic force microscopy(AFM),and ultraviolet-visible(UV-Vis)spectroscopy.Photoinduced cascading electron/charge transfer from Por to RGO and from RGO to Pc was established from fluorescence,electrochemical,and femtosecond transient absorption(fs-TA)spectroscopy studies.The increased distance between the electron donors and acceptors of the Por-RGO-Pc nanoconjugate compared to the parent materials and the intermediate RGO-Pc results in longlived charge separation,and an enhancement in nonlinear optical(NLO)absorption(a large NLO coefficient of about 827.44 cm/GW)towards nanosecond laser irradiation at 532 nm.

Dramatic femtosecond nonlinear absorption at a strongly coupled porphyrin-graphene nanoconjugate

Edge-functionalization of graphene is emerging as a powerful chemical method for the construction ofπ-delocalized highlyplanar graphene nanoconjugates that are not accessible through surface-supported syntheses.Herein,a graphene-porphyrin nanoconjugate via a robust pyrazine(pz)linkage has been obtained by condensing 2,3-diamino-5,10,15,20-tetraphenylporphyrin(DA-TPP)with ortho-quinone(o-quinone)moieties at edge sites of graphene oxide(GO).The as-prepared GO-pz-TPP exhibits an intense absorption extending from 375 to 900 nm and a high quenching yield(98%)of fluorescence,indicating a strong electronic coupling effect between GO and TPP units.GO-pz-TPP displays strong nonlinear optical(NLO)absorption and giant NLO coefficients with 800 and 1,030 nm fs laser,in sharp contrast to traditional graphene-porphyrin nanohybrids only NLO-active towards ns laser.Such a dramatic NLO performance towards femtosecond pulsed laser has not been achieved in any carbonchromophores nanohybridized materials to date.This work validates theπ-extended edge-functionalization strategy as a means to tune the NLO properties of graphene,thereby providing a new paradigm for the assembly of versatile optoelectronic materials.

Strong near-infrared and ultrafast femtosecond nonlinearities of a covalently-linked triply-fused porphyrin dimer-SWCNT nanohybrid

Functional materials displaying large ultrafast third-order optical nonlinearities across a wide spectral region and broad temporal domain are required for all-optical signal processing.Particularly desirable is nonlinear optical(NLO)activity at near-infrared(NIR)wavelengths with femtosecond pulses.Herein the first triply-fused porphyrin dimer(TFP)-functionalized single-walled carbon nanotube(SWCNT)nanohybrid was successfully constructed by covalently grafting TFPs onto SWCNT.The results of Z-scan techniques demonstrate that the newly obtained TFP-SWCNT nanohybrid was found with a strong NLO performance under both nanosecond and femtosecond irradiation.In the nanosecond regime,an enhancement in optical limiting(OL)of the TFP-SWCNT nanohybrid is seen at 532 nm when compared with the performance of porphyrin monomer-functionalized SWCNT nanohybrid Por-SWCNT.Under femtosecond irradiation,the TFP-SWCNT nanohybrid exhibits a particularly strong OL effect with a giant two-photon absorption(TPA)cross section value(ca.15,500 GM)at 800 nm pulses that mainly stems from intense TPA of TFP,in sharp contrast to the Por-SWCNT nanohybrid which exhibits only saturable absorption under identical irradiation.These results demonstrate that the newly-developed TFP-SWCNT nanohybrid is a very promising OL candidate for practical applications across wide spectral and temporal domains,and that covalently functionalizing carbon-based materials with triply-fused chromophores may be a useful approach to engineering adaptable photonic devices with broad-ranging NLO activity.