Effect of chain length and donor–acceptor substitution on the electrical responsive properties of conjugated biphenyls: a DFT-based computational study

<p>The effect of donor–acceptor (D-A) substituent and chain length on the electrical polarisabilities and first hyper polarisability of cis and trans biphenyl oligomeric compounds have been investigated using density functional theory-based hybrid functional CAM-B3LYP with 6-311G (2d,2p) basis set. Our extensive computational study reveals that both average polarisability and first hyper polarisability of the studied compounds increase with the increasing ethylene spacer chain length. Again the substitution of donor (NMe₂) and acceptor (C≡N) at the para position of the phenyl rings to each oligomer shows order of magnitude increase of both <i>α</i>_av and <i>β</i>_av value compared to the unsubstituted one. This increased <i>α</i>_av and <i>β</i>_av values have been explained due to increasing charge transfer contribution resulting from decreasing optical energy gap (Δ<i>E</i> = <i>S</i>₁ − <i>S</i>₀) upon D-A substitution. It is also observed that the charge transfer contribution to first hyperpolarisability (<i>β</i>_CT) is more than the polarisability (<i>α</i>_CT) for the studied molecules. The electronic spatial extent (<<i>R</i>²>) which is a measure of electron density volume around the molecule is found to play a major role along with the intramolecular charge transfer character to explain the non-linear variation of first hyperpolarisability (<i>β</i>_av) as a function of ethylene spacer chain length (<i>n</i>) and D-A substitution.</p

Microwave-assisted synthesis of anisotropic gold nanocrystals in polymer matrix and their catalytic activities

<div><p>We report a facile and fast one-pot microwave (MW) synthesis of gold nanotriangle, nanobranches and nanorod. Gold salt is reduced to gold nanoparticles by ethylene glycol/polyethylene glycol in the presence of hydroxypropyl methyl cellulose. Morphology of the nanocrystals can be tailored by varying the amount of capping agents, reducing agent and the MW irradiation time. Synthesised nanoparticles are characterised by ultraviolet–visible (UV–Vis), transmission electron microscopic and X-ray diffraction spectroscopy study. The key requirement for producing the gold triangle and gold nanorod of higher aspect ratio is the adequate MW heating time. The photocatalytic activity of gold nanocrystals is investigated by monitoring the photochemical reduction of 2,4,6-trinitrophenol (TNP) in the presence of excess NaBH₄. The reaction is first order with respect to the concentration of TNP. It has been observed that the catalytic efficiency of rod-like gold nanocrystals is higher than the other gold nanocrystals.</p></div

Computation of global reactivity descriptors and first hyper polarisability as a function of torsional angle of donor–acceptor substituted biphenyl ring system

<p>Global reactivity descriptors, e.g. average polarisabilty (α_av), chemical hardness (η), electrophilicity index (ω) of two donor–acceptor substituted biphenyl, i.e. Dimethyl-(4ʹ-Nitro-biphenyl-4-yl)-amine (NBA) and 4ʹ-Dimethylamino-biphenyl-4carbonitrile (DBC), were computed along the torsional potential of two biphenyl ring systems. Density functional-based hybrid functional B3LYP with 6-31G(d) basis were used to all the computational study. It is observed that variation of the global reactivity descriptors η, ω as a function of torsional angle of biphenyl ring of NBA are in accordance with the maximum hardness and minimum electrophilicity principle. But the variations of α_av, η, ω for DBC and α_av for NBA are not in accordance with the respective extremum principles. These apparent violations of extremum principles have been explained as the non-constancy of external potential within the tolerance limit for the respective parameters during the variation of torsional angle. The variation of first hyperpolarisability (β_av) as a function of dihedral angle has been explained with the extent of charge transfer character of conformers for both NBA and DBC. It is also observed that the variation of first hyper polarisability is a function of <i>S</i>₀ − <i>S</i>₁ optical energy gap rather than HOMO–LUMO gap of the titled compounds.</p

Pyrene Scaffold as Real-Time Fluorescent Turn-on Chemosensor for Selective Detection of Trace-Level Al(III) and Its Aggregation-Induced Emission Enhancement

A pyrene based fluorescent probe, 3-methoxy-2-((pyren-2yl-imino)­methyl)­phenol (HL), was synthesized via simple one-pot reaction from inexpensive reagents. It exhibited high sensitivity and selectivity toward Al³⁺ over other relevant metal ions and also displayed novel aggregation-induced emission enhancement (AIEE) characteristics in its aggregate/solid state. When bound with Al³⁺ in 1:1 mode, a significant fluorescence enhancement with a turn-on ratio of over ∼200-fold was triggered via chelation-enhanced fluorescence through sensor complex (Al-L) formation, and amusingly excess addition of Al³⁺, dramatic enhancement of fluorescence intensity over manifold through aggregate formation was observed. The 1:1 stoichiometry of the sensor complex (Al-L) was calculated from Job’s plot based on UV–vis absorption titration. In addition, the binding site of sensor complex (Al-L) was well-established from the ¹H NMR titrations and also supported by the fluorescence reversibility by adding Al³⁺ and EDTA sequentially. Intriguingly, the AIEE properties of HL may improve its impact and studied in CH₃CN–H₂O mixtures at high water content. To gain insight into the AIEE mechanism of the HL, the size and growth process of particles in different volume percentage of water and acetonitrile mixture were studied using time-resolved photoluminescence, dynamic light scattering, optical microscope, and scanning electron microscope. The molecules of HL are aggregated into ordered one-dimensional rod-shaped microcrystals that show obvious optical waveguide effect