Synthesis and Opto-electronic Properties of BODIPY o-OPhos Systems

Herein, we report the versatile synthetic strategy and opto-electronic properties for the phosphorylation of BODIPY derivatives 5aa - 5ak by substituting with an electron-donating/withdrawing group at the ortho position. Nevertheless, this new methodology relatively promotes the tolerance of the aldehyde moiety and the high yield for the synthesis of BODIPY o-OPhos derivatives. The photophysical studies suggest improved optical properties due to the inductive effect of various electron-donating/withdrawing groups. The UV-visible and the emission data suggest that BODIPY o-OPhos derivatives emphasize the property of the excited states with an increase in fluorescence intensity and high quantum yields due to the presence of bulky phospsho-triester at the meso- position which hinders the free rotation around the C-Ar bond and facilitates the development of OLEDs and various organophosphorus warfare agents. Electrochemical studies reveal 5ak depicts the ease of redox activity amongst the 5aa - 5ak derivatives. The density functional theory indicates the highest occupied molecular orbital on the BODIPY moiety whereas the lowest unoccupied molecular orbital delocalized on BODIPY and the phospho-triester moieties. Thus, the unique development of the novel BODIPY derivatives with improved optical and redox properties pave the way for fluorescent probes and bioimaging techniques.     

Photoinduced electron transfer in bisporphyrin-diimide complexes

The bisporphyrin host ZnH was synthesized, and its complexation with two aromatic diimide guest molecules, bis(pyridyl)naphthalenediimide NIN and bis(pyridyl)phenyldiimide PIN, was investigated by (1)H NMR and UV/Vis spectroscopy. The diimide guests were complexed simultaneously with both metalloporphyrins of the host, with association constants on the order of 10(8)M(-1). The processes occurring in the complex after excitation of the porphyrinic host were studied by steady-state and time-resolved emission and transient absorption spectroscopy. Complexation alters the photophysical properties of the host ZnH; the luminescence bands shift to the red by 30 nm in the complexed forms, while the emission quantum yield and the lifetime decrease. Comparison of a complex between ZnH and a model guest unable to undergo photoinduced processes allowed us to establish that, in the diimide complexes, quenching of the porphyrinic luminescence occurs with a rate of 1.1 x 10(10)s(-1). The process is identified as an electron transfer from the excited singlet of the porphyrinic host to the imide guest, which yields charge-separated states with a lifetime of 710 ps for ZnH(+)-NIN(-) and 260 ps for ZnH(+)-PIN(-).     

Unprecedented Charge‐Transfer Complex of Fused Diporphyrin as Near‐Infrared Absorption‐Induced High‐Aspect‐Ratio Nanorods

Charge‐transfer (CT) complexes of near‐infrared absorbing systems have been unknown until now. Consequently, structural similarities between donor and acceptor are rather important to achieve this phenomenon. Herein, we report electron donors such as non‐fused diporphyrin‐anthracene (DP), zinc diporphyrin‐anthracene (ZnDP) and fused zinc diporphyrin‐anthracene (FZnDP) in which FZnDP absorbs in NIR region and permits a CT complex with the electron acceptor, perylene diimide (PDI ) in CHCl₃ exclusively. UV/Vis‐NIR absorption, ¹H NMR, NOESY and powder X‐ray diffraction analysis demonstrated that the CT complex formation occurs by π–π stacking between perylene units in FZnDP and PDI upon mixing together in a 1:1 molar concentration in CHCl₃, unlike non‐fused ZnDP and DP. TEM and AFM images revealed that the CT complex initially forms nanospheres leading to nanorods by diffusion of CH₃OH vapors into the CHCl₃ solution of FZnDP/PDI (1:1 molar ratio). Therefore, these CT nanorods could lead to significant advances in optical, biological and ferroelectric applications.     

Recent Advances of Cobalt(II/III) Redox Couples for Dye‐Sensitized Solar Cell Applications

In recent years dye‐sensitized solar cells (DSSCs) have emerged as one of the alternatives for the global energy crisis. DSSCs have achieved a certified efficiency of >11% by using the I^?/I₃^? redox couple. In order to commercialize the technology almost all components of the device have to be improved. Among the various components of DSSCs, the redox couple that regenerates the oxidized sensitizer plays a crucial role in achieving high efficiency and durability of the cell. However, the I^?/I₃^? redox couple has certain limitations such as the absorption of triiodide up to 430 nm and the volatile nature of iodine, which also corrodes the silver‐based current collectors. These limitations are obstructing the commercialization of this technology. For this reason, one has to identify alternative redox couples. In this regard, the Co(II/III) redox couple is found to be the best alternative to the existing I^?/I₃^? redox couple. Recently, DSSC test cell efficiency has risen up to 13% by using the cobalt redox couple. This review emphasizes the recent development of Co(II/III) redox couples for DSSC applications.     

Isophorone‐boronate ester: A simple chemosensor for optical detection of fluoride anion

A highly selective isophorone‐boronate ester based chemosensor, ( 1 ) , having a dicyanovinyl moiety as a convenient colorimetric probe, has been designed. Different types of anionic analyte such as CH₃COO^?, ClO₄^?, Cl^?, F^?, PF₆^?, Br^? and HSO₄^? were tested and among them only highly nucleophilic F^? anion displayed significant response towards the sensor. Addition of the fluoride anion across the boron atom disrupts the π‐conjugation thereby shifts the absorption wavelength towards the redshift region due to the decrease in the HOMO‐LUMO energy gap and a colour change from yellow to blue is observed under visible light condition. The detection limit of this probe was calculated to be 3.25 × 10^—8 M for fluoride anion. The binding constants and the detection limits of the sensor were calculated using absorption titration studies. The silica gel TLC strips dip‐coated by the chemosensor ( 1 ) revealed a colour change from yellow to brick red to naked eye.     

α-Fe2O3 nanoflowers: synthesis,characterization, electrochemical sensing and photocatalytic property

Nanoflower structured α-Fe₂O₃ was synthesized by adding hexamine to an aqueous solution of ferrous sulphate followed by drying and annealing at 600 °C for 6 h. X-ray diffraction analysis, Fourier-transformed infrared spectroscopy, Raman and DRS UV–visible absorption spectroscopy showed the formation of α-Fe₂O₃ with good crystalline nature. Field emission-scanning electron microscopy investigation revealed that the α-Fe₂O₃ has flower-like morphology, which is composed of nanorods. Cyclic voltammetry and chronoamperometry were used to investigate their electrochemical sensing property towards uric acid (UA). α-Fe₂O₃ exhibited enhanced sensing behavior with respect to that of bare GCE. Additionally, the α-Fe₂O₃ nanoflowers exhibit better photocatalytic activity of up to 71.7 % against rhodamine B (RhB) in short time of 60 min under visible light irradiation. It is found that the smaller crystallite size and flower-like morphology play a vital role in allowing an interaction between α-Fe₂O₃ and UA or RhB dye which enhances both the electrochemical sensing and photocatalytic activity.     

Ultrafast Photoinduced Charge Separation Leading to High‐Energy Radical Ion‐Pairs in Directly Linked Corrole–C60 and Triphenylamine–Corrole‐C60 Donor–Acceptor Conjugates

Closely positioned donor–acceptor pairs facilitate electron‐ and energy‐transfer events, relevant to light energy conversion. Here, a triad system TPACor‐C₆₀ , possessing a free‐base corrole as central unit that linked the energy donor triphenylamine ( TPA ) at the meso position and an electron acceptor fullerene (C₆₀) at the β‐pyrrole position was newly synthesized, as were the component dyads TPA‐Cor and Cor‐C₆₀ . Spectroscopic, electrochemical, and DFT studies confirmed the molecular integrity and existence of a moderate level of intramolecular interactions between the components. Steady‐state fluorescence studies showed efficient energy transfer from ¹ TPA* to the corrole and subsequent electron transfer from ¹corrole* to fullerene. Further studies involving femtosecond and nanosecond laser flash photolysis confirmed electron transfer to be the quenching mechanism of corrole emission, in which the electron‐transfer products, the corrole radical cation ( Cor^?+ in Cor‐C₆₀ and TPA‐Cor^?+ in TPACor‐C₆₀ ) and fullerene radical anion (C₆₀^??), could be spectrally characterized. Owing to the close proximity of the donor and acceptor entities in the dyad and triad, the rate of charge separation, k_CS, was found to be about 10¹¹ s^?1, suggesting the occurrence of an ultrafast charge‐separation process. Interestingly, although an order of magnitude slower than k_CS, the rate of charge recombination, k_CR, was also found to be rapid (k_CR≈10¹⁰ s^?1), and both processes followed the solvent polarity trend DMF>benzonitrile>THF>toluene. The charge‐separated species relaxed directly to the ground state in polar solvents while in toluene, formation of ³corrole* was observed, thus implying that the energy of the charge‐separated state in a nonpolar solvent is higher than the energy of ³corrole* being about 1.52 eV. That is, ultrafast formation of a high‐energy charge‐separated state in toluene has been achieved in these closely spaced corrole–fullerene donor–acceptor conjugates.     

Sensing of picric acid with a glassy carbon electrode modified with CuS nanoparticles deposited on nitrogen-doped reduced graphene oxide

We describe the preparation of a nanohybrid consisting of nitrogen doped reduced graphene oxide and CuS nanoparticles (N-rGO/CuS) by in-situ microwave irradiation at weight ratios of 25/75, 50/50, and 75/25. The resulting nanohybrids were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, FTIR, spectroscopy, scanning electron and transmission electron microscopy, electrochemically by cyclic voltammetry and electrochemical impedance analysis. It is shown that the CuS nanoparticles are evenly decorated onto the N-rGO surface. The nanohybrids was placed on glassy carbon electrode (GCE) where they showed electro-reductive activity towards picric acid, typically at working voltages between ?0.2 and ?0.8 V (vs. SCE). Effects of pH value and scan rate were evaluated, and it is shown that two electrons are involved in electro-reduction. The detection limits of the GCE modified with various N-rGO/CuS hybrids (with 25/75, 50/50, and 75/25 wt%) are 6.2, 3.2, and 0.069 μM respectively. The method demonstrates its applicability in sensing of picric acid with good reproducibility.

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Graphical abstract Nitrogen doped reduced graphene oxide nanohybrids was synthesized for the detection of picric acid. A straightforward and preconcentration free analysis of picric acid was successfully demonstrated at nanomolar levels using the nanohybrids.