Push–Pull Porphyrins via β-Pyrrole Functionalization: Evidence of Excited State Events Leading to High-Potential Charge-Separated States

A new set of free-base and zinc(II)-metallated, β-pyrrole-functionalized unsymmetrical push–pull porphyrins were designed and synthesized via β-mono- and dibrominated tetraphenylporphyrins using Sonogashira cross-coupling reactions. The ability of donors and acceptors on the push–pull porphyrins to produce high-potential charge separated states was investigated. The porphyrins were functionalized at the opposite β,β′-pyrrole positions of porphyrin ring bearing triphenylamine push groups and naphthalimide pull groups. Systematic studies involving optical absorption, steady-state and time-resolved emission revealed existence of intramolecular type interactions both in the ground and excited states. The push–pull nature of the molecular systems was supported by frontier orbitals generated on optimized structures, wherein delocalization of HOMO over the push group and LUMO over the pull group connecting the porphyrin π-system was witnessed. Electrochemical studies were performed to visualize the effect of push and pull groups on the overall redox potentials of the porphyrins. Spectroelectrochemical studies combined with frontier orbitals helped in characterizing the one-electron oxidized and reduced porphyrins. Finally, by performing transient absorption studies in polar benzonitrile, the ability of push–pull porphyrins to produce charge-separated states upon photoexcitation was confirmed and the measured rates were in the range of 10⁹ s⁻¹. The lifetime of the final charge separated state was around 5 ns. This study ascertains the importance of push–pull porphyrins in solar energy conversion and diverse optoelectronic applications, for which high-potential charge-separated states are warranted.     

Effect of concentration on the photo-orientation and relaxation dynamics of self-assembled monolayers of mixtures of an azobenzene-based triethoxysilane with octyltriethoxysilane

Self-assembled monolayers (SAMs) were prepared from solutions with different proportions of a photoactive, azobenzene-based, silanized derivative of disperse red one (dDR1), and octyltriethoxysilane (OTE), a shorter, nonphotoactive molecule. The in-plane photoinduced orientational ordering of the resulting two component monolayers was monitored via precision measurement of in-plane birefringence using a dedicated high-extinction polarimeter. Measurements of contact angle, absorption, and birefringence show that introduction of OTE into the dDR1 deposition solution produces a continuous reduction of the surface density of dDR1 in the SAM, enabling the study of photowriting and relaxation dynamics in monolayers ranging from 100% dDR1 to samples where the dDR1 coverage is about 35%. The orientational dynamics depend strongly on the areal density of dDR1. As the fractional area of dDR1 is reduced, the rates of photowriting, photoerasing, and thermal relaxation increase, and the local orientational confinement of the molecules becomes more heterogeneous.     

Improved inhomogeneous Strichartz estimates for the Schrödinger equation

We study inhomogeneous Strichartz estimates for the Schrödinger equation for dimension n?3. Using a frequency localization, we obtain some improved range of Strichartz estimates for the solution of inhomogeneous Schrödinger equation except dimension n=3.     

Electrical and Sensing Properties of Single‐Walled Carbon Nanotubes Network: Effect of Alignment and Selective Breakdown

The electrical transport and NH₃ sensing properties of randomly oriented and aligned SWNT networks were presented and discussed. The results indicate that aligned SWNT‐FETs have better FET characteristics due to the reduced number of interconnected nodes. This was particularly true as the resistance of the devices increased. Gated electrical breakdown was implemented to selectively remove metallic (m‐) SWNTs, thereby reducing scattering centers. This technique provided significant improvements in FET characteristics resulting in greater on/off ratio (e.g. 10⁴). AC dielectrophoretic alignment followed by selective electrical breakdown of m‐SWNTs can significantly enhance the semiconducting properties of SWNT networks which resulted in highly sensitive sensors.     

DNA Assisted Assembly of Multisegmented Nanowires

This work demonstrates a highly specific and selective assembly of multisegmented nanowires on prepatterned gold electrodes using DNA hybridization. Multisegmented Au/Pd/Au nanowires were synthesized using template‐directed electrodeposition. Two complementary single‐stranded DNAs modified with thiol tags adsorb on gold electrodes and gold segments of nanowires, and enable the nanowires to assemble across electrodes. The assembled nanowires show ohmic contact with minimum contact resistance. Using these nanowires, the temperature dependent electrical resistance and the sensing performance toward hydrogen were investigated. The temperature coefficient of resistance of nanowires was lower than bulk polycrystalline counterpart, because of higher electron scattering at the surface and grain boundaries of nanowires. The nanowires were sensitive toward hydrogen gas at room temperature with a detection limit of 0.5%.     

Excited‐State Charge Transfer in Covalently Functionalized MoS2 with a Zinc Phthalocyanine Donor–Acceptor Hybrid

The functionalization of MoS₂ is of paramount importance for tailoring its properties towards optoelectronic applications and unlocking its full potential. Zinc phthalocyanine (ZnPc) carrying an 1,2‐dithiolane oxide linker was used to functionalize MoS₂ at defect sites located at the edges. The structure of ZnPc‐MoS₂ was fully assessed by complementary spectroscopic, thermal, and microscopy imaging techniques. An energy‐level diagram visualizing different photochemical events in ZnPc‐MoS₂ was established and revealed a bidirectional electron transfer leading to a charge separated state ZnPc^{. +} ‐MoS₂^.?. Markedly, evidence of the charge transfer in the hybrid material was demonstrated using fluorescence spectroelectrochemistry. Systematic studies performed by femtosecond transient absorption revealed the involvement of excitons generated in MoS₂ in promoting the charge transfer, while the transfer was also possible when ZnPc was excited, signifying their potential in light‐energy‐harvesting devices.     

Janus Graft Block Copolymers: Design of a Polymer Architecture for Independently Tuned Nanostructures and Polymer Properties

The graft‐through synthesis of Janus graft block copolymers (GBCPs) from branched macromonomers composed of various combinations of homopolymers is presented. Self‐assembly of GBCPs resulted in ordered nanostructures with ultra‐small domain sizes down to 2.8 nm (half‐pitch). The grafted architecture introduces an additional parameter, the backbone length, which enables control over the thermomechanical properties and processability of the GBCPs independently of their self‐assembled nanostructures. The simple synthetic route to GBCPs and the possibility of using a variety of polymer combinations contribute to the universality of this technique.     

Metal oxide-modified ZnO/SiO <Subscript>2</Subscript> catalysts for cyclo-dehydrogenation of ethylenediamine with propyleneglycol to 2-methylpyrazine

Metal oxide-modified ZnO /SiO2 catalysts were studied for the cyclo-dehydrogenation of ethylenediamine with propyleneglycol to 2-methylpyrazine at 633 K. The ZnO/SiO₂ catalyst showed fairly good ethylenediamine conversion and quantitative propyleneglycol conversion with about 60 mol% of 2-methylpyrazine selectivity, which is due to the existence of large amount of unconverted intermediate, 2-methylpiperazine. Metal oxide (CuO, NiO, Co₃O₄)-modified ZnO/SiO₂ catalysts were prepared to facilitate the dehydrogenation of 2-methylpiperazine to 2-methylpyrazine. About 82 mol% of 2-methylpyrazine selectivity was achieved on CuO and Co₃O₄ modified ZnO/SiO₂ catalysts, with significant increases of pyrazine selectivity. The catalytic properties of the metal oxidemodified ZnO/SiO₂ catalysts, pretreated with hydrogen gas as in the cyclo-dehydrogenation, were compared using the well-known probe reaction, the dehydrogenation/ dehydration of cyclohexanol to cyclohexanone or phenol/cyclohexene. The selectivities of pyrazine in the cyclo-dehydrogenation on the metal oxide-modified ZnO/SiO₂ catalysts were correlated with the phenol selectivities of the probe reaction. It is proposed that the metallic site of catalyst is responsible for the formation of pyrazine from ethylenediamine dimerization. The improved 2-methylpyrazine yield on CuO/ZnO/SiO₂ catalyst was explained by the proper adjustment of catalytic properties, which could be differentiated by the phenol selectivity in the cyclohexanol probe reaction. Thus, the large enhancement of 2-methylpiperazine dehydrogenation to 2-methylpyrazine and the suppression of excess pyrazine formation are supposed to occur on the metallic Cu formed in situ during the reaction during the cyclo-dehydrogenation of ethylenediamine with propyleneglycol.     

Bochner–Riesz Means with Respect to a Generalized Cylinder

We study the L ^p boundedness of the generalized Bochner–Riesz means S ^λ which are defined as $$S^{\lambda}f(x) = \mathcal{F}^{-1} \left[\left(1 - \rho \right)_{+}^{\lambda} \widehat{f} \right](x)$$ where ${\rho(\xi) = {\rm max}\{|\xi_{1}|, \ldots, |\xi_{\ell}|\}}$ for ${\xi = (\xi_{1},\ldots, \xi_{\ell}) \in \mathbb{R}^{{d}_{1}} \times \cdots \times \mathbb{R}^{{d}_{\ell}}}$ and ${\mathcal{F}^{-1}}$ is the inverse Fourier transform.     

Morphology and crystal phase evolution of doctor-blade coated CuInSe2 thin films

CuInSe₂ (CIS) chalcopyrite thin films were prepared using a low-cost, non-vacuum doctor-blade coating and the thermal annealing method. An acetone-based precursor solution containing copper chloride, indium chloride, selenium chloride, and an organic binder was deposited onto a Mo-sputtered soda lime glass substrate using a doctor-blade coating method. After coating, the precursor films were annealed in a quartz tube furnace under low vacuum without the use of a Se atmosphere or reduction conditions. Evolution of the morphology, crystal structure, and thermal decomposition behavior of the films was analyzed by X-ray diffraction, scanning electron microscopy, and thermogravimetric analysis, and the film formation mechanism was suggested. The as-deposited precursor film gradually decomposed with increase in temperature and formed Cu_2−xSe and In₂Se₃ nuclei on the surface of the film. Incorporation of Cu_2−xSe with In₂Se₃ yielded a chalcopyrite CIS phase, which crystallized on annealing above 400 °C. The obtained CIS film showed low-resistive ohmic behavior with a Mo electrode and a high absorption efficiency for visible–infrared (IR) light, making it suitable for use in photovoltaic applications.