Covalent organic frameworks (COFs) have garnered immense scientific interest among porous materials because of their structural tunability and diverse properties. However,the response of such materials towardlaser-induced nonlinear optical (NLO) applications is hardly understood and demands prompt attention. Three novel regioregular porphyrin (Por)-based porous COFs-Por-COF-HH and its dual metalated congeners Por-COF-ZnCu and Por-COF-ZnNi-have been prepared and present excellent NLO properties.N otably,i ntensity-dependent NLO switching behavior was observed for these Por-COFs,w hichi sh ighly desirable for optical switching and optical limiting devices. Moreover,t he efficient p-conjugation and charge-transfer transition in ZnCu-Por-COF enabled ahigh nonlinear absorption coefficient (b = 4470 cm/GW) and figure of merit (FOM = s 1 /s o ,3565) value compared to other state-of-the-art materials, including molecular porphyrins (b % 100-400 cm/GW), metalorganic frameworks (MOFs; b % 0.3-0.5 cm/GW), and graphene (b = 900 cm/GW). Molecules/materialswithinherentnonlinearoptical(NLO)properties have profound importance in telecommunications, data storage,d isplay technologies,s ensors,a nd biomedical devices. [1] In this regard, molecular porphyrins have been widely studied because of their versatile optical and electrochemical properties,large and fast NLO responses,possibility of incorporating aw ide range of metals,a nd their good thermochemical stabilities for optical limiting and optical switching applications. [2] Nonetheless,t oenhance and tune optical nonlinearities of singular porphyrin moieties,b athochromic shifting of their absorption bands by large p-electron delocalization is crucial, which becomes possible through de novo design of integrated porphyrin units featuring extended p-conjugation. [3, 4] Along this line,w ep ropose ap orphyrin-linked covalent organic framework (COF) [5] as model system, wherein enhancement and switching of the NLO response can be studied by manipulation of the framework. Among the recognized crystalline materials, COFs are known for being mechanically robust and offering ahighly accessible surface area. Thestructural and electronic tunability of COFs have garnered particular interest in research areas such as adsorption/storage, [6] chemical sensors, [7] electronics, [8] and catalysis. [9] Despite such potential, COFs comprising porphyrin units have not been explored as NLO materials.F or this purpose,aregioregular ordering of multiple metal centers in ac rystalline 2D porphyrin framework-preferably without ap ost-synthetic modification-is desirable.T his challenging objective [10] has great potential in optoelectronics and photo/electrocatalysis applications.Herein, we present aconjugated imine-linked porphyrinhomopolymeric COF (Por-COF-HH; Figure 1a)prepared by Schiff base A4B4 condensation of 5,10,15,20-tetrakis(4-formylphenyl)-21H,23H-porphyrin (TFPP) and 5,10,15,20-tetrakis(4-aminophenyl)-21H,23H-porphyrin (TAPP). Adopting the same pathway,w ea lso synthesized regioregular...

Rare earth-activated 1-D photonic crystals were fabricated by RF-sputtering technique. The cavity is constituted by an Er3+-doped SiO2 active layer inserted between two Bragg reflectors consisting of ten pairs of SiO2/TiO2 layers. Scanning electron microscopy is employed to put in evidence the quality of the sample, the homogeneities of the layers thickness and the good adhesion among them. Near infrared transmittance and variable angle reflectance spectra confirm the presence of a stop band from 1500 nm to 2000 nm with a cavity resonance centered at 1749 nm at 0° and a quality factor of 890. The influence of the cavity on the ⁴I₁₃/₂ -->⁴I₁₅/₂ emission band of Er3+ ion is also demonstrated.

The metal−semiconductor heterostructures have recently emerged as a new class of functional materials for their potential applications due to plasmonexciton interactions. Here, we demonstrate the nonlinear optical switching and enhanced nonlinear optical response of Au−CdSe heterostructures. The nonlinear optical properties of CdSe quantum dots and Au−CdSe heteronanostructures are investigated by using a Z-scan technique at 532 nm picosecond laser pulses, and 800 nm femtosecond laser pulses. Interestingly, we observe switching behavior from saturable absorption (SA) to reverse saturable absorption (RSA) with increasing laser intensity. The effective two-photon absorption cross section (σ eff ) of Au−CdSe heteronanostructures is greatly enhanced which is attributed to charge transfer between CdSe and Au nanoparticles. The nonlinear refraction changes its sign from positive to negative nonlinearity at higher intensities for Au−CdSe heterostructures. Third order nonlinear optical susceptibility is being measured by using the DFWM technique at 532 nm. Similar switching behavior is observed in Au−CdSe heteronanostructures at nonresonant excitations (800 nm), where a CdSe quantum dot shows reverse saturable absorption behavior attributed to the two-photon absorption. The optical switching behavior of these heterostructures could play a potential role in photonics and optoelectronic applications.

No abstract

Polyaniline (PANI) is one of the most common polymers known for its conducting properties. However, poor water solubility limits its applications. In this work, PANI has been functionalized with sulfonic acid groups to produce sulfonated PANI (SPANI) offering excellent solubility in water. To compensate for the decrease of electrical conductivity due to functionalization, SPANI was combined with reduced graphene oxide (RGO) to form SPANI/RGO composites with interesting optical, thermal, and electrical properties. The composites have been characterized using X‐ray diffraction (XRD), field emission scanning electron microscopy, UV–vis absorption spectroscopy, Raman spectroscopy, Fourier‐transform infrared spectroscopy, X‐ray photoelectron spectroscopy, thermogravimetric analysis, cyclic voltammetry, and four probe electrical conductivity measurement. The SPANI/RGO composites show increased thermal stability, reduced optical band gap and improved electrochemical properties compared with the pure polymer. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42766.