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.

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.

Machine learning assisted prediction of charge transfer properties in organic solar cells by using morphology-related descriptors

Charge transfer and transport properties are crucial in the photophysical process of exciton dissociation and recombination at the donor/acceptor(D/A)interface.Herein,machine learning(ML)is applied to predict the charge transfer state energy(ECT)and identify the relationship between ECT and intermolecular packing structures sampled from molecular dynamics(MD)simulations on fullerene-and non-fullerene-based systems with different D/A ratios(RDA),oligomer sizes,and D/A pairs.The gradient boosting regression(GBR)exhibits satisfactory performance(r=0.96)in predicting ECT withπ-packing related features,aggregation extent,backbone of donor,and energy levels of frontier molecular orbitals.The charge transport property affected byπ-packing with different RDA has also been investigated by space-charge-limited current(SCLC)measurement and MD simulations.The SCLC results indicate an improved hole transport of non-fullerene system PM6/Y6 with RDA of 1.2:1 in comparison with the 1:1 counterpart,which is mainly attributed to the bridge role of donor unit in Y6.The reduced energetic disorder is correlated with the improved miscibility of polymer with RDA increased from 1:1 to 1.2:1.The morphology-related features are also applicable to other complicated systems,such as perovskite solar cells,to bridge the gap between device performance and microscopic packing structures.

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.

Synergistic regulation of intermolecular interactions to control chiral structures for chiral recognition

Understanding the regulatory mechanism of self-assembly processes is a necessity to modulate nanostructures and their properties. Herein, we have studied the mechanism of self-assembly in the C3 symmetric 1,3,5-benzentricarboxylic amino acid methyl ester enantiomers(TPE) in a mixed solvent system consisting of methanol and water. The resultant chiral structure was used for chiral recognition. The formation of chiral structures from the synergistic effect of multiple noncovalent interaction forces was confirmed by various techniques. Molecular dynamics simulations were used to characterize the time evolution of TPE structure and properties in solution. The theoretical results were consistent with the experimental results. Furthermore, the chiral structure assembled by the building blocks of TPE molecules was highly stereoselective for diamine compounds.