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To shed the light about the effect of the linkers of the small organic molecules on their optical properties, we examine herein the linear, and nonlinear optical properties of the two easy synthesized push–pull compounds 1 and 2 bearing similar donor and acceptor moieties based on stilbene derivatives, but differ in the spacer group, namely 4-cyano-4′-(N-dihexylamino) stilbene (1), and 4-cyanobenzal-4′-(N,N-diethyl) aniline (2). The optical studies were initially examined using various spectroscopic techniques. Compounds 1 and 2 exhibited strong absorption bands in the visible spectra with maxima at 400 and 429 nm, respectively. The steady-state emission measurements of 1 with its π–π* transition showed a strong emission band at 500 nm with a fluorescence quantum yield (Φf) of 0.30, which is much higher than that of 2 with its n–π* transition (Φf = 0.004) reflecting the nature of singlet state on the optical emission properties. The cyclic voltammograms showed the oxidation potentials of 1 and 2 at 670 and 840 mV versus Ag/AgCl, respectively, confirm the effect of the inkers on their electrochemical properties. Unlike compound 2, the thin film of 1 exhibited a sharp absorption edge at 360 nm suggesting its usefulness as an excellent UV-cut optical filter. The nonlinear absorption coefficients of the examined compounds were measured using the Z-scan technique. Compounds 1 and 2 were both exposed to 100 fs laser pulses using different excitation wavelengths. The obtained positive nonlinear absorption coefficient values of 1 and 2, such positive values may be caused by reverse saturable absorption. The influence of the laser parameters (in particular, excitation wavelength, and incident peak intensity) on the nonlinear absorption coefficient of 1 and 2 has been examined. These observations suggest the significant effect of linkers on both the photophysical, linear, and nonlinear optical features of 1 (with C=C linker) compared to 2 (with C=N linker). Furthermore, the DFT/TD-DFT methods at 6-31+G(d,p) were performed to predict the geometric, electronic, and optical properties of 1 and 2. [ABSTRACT FROM AUTHOR]

2-Mercaptobenzothiazole (2-MBT) in a solution of 0.5 M HCl is an effective corrosion inhibitor for aluminum and aluminum–titanium alloys. Tafel polarization and electrochemical impedance spectroscopy (EIS) were employed to assess this heterocyclic compound's anticorrosive potential and complementary by scanning electron microscope (SEM) and calculating porosity percentage in the absence and presence of various inhibitor concentrations. Inhibition efficiency (IE%) was strongly related to concentration (10–6–10–3 M). Temperature's effect on corrosion behavior was investigated. The data exhibited that the IE% decreases as the temperature increases. An increase in activation energy (Ea) with increasing the inhibitor concentration and the decrease in the IE% value of the mentioned compound with raising the temperature indicates that the inhibitor molecules are adsorbed physically on the surface. Thermodynamic activation parameters for Al and Al–Ti alloy dissolution in both 0.5 M HCl and the inhibited solution were calculated and discussed. According to Langmuir's adsorption isotherm, the inhibitor molecules were adsorbed. The evaluated standard values of the enthalpy ( Δ H a d s. o) , entropy ( Δ S a d s. o) and free energy changes ( Δ G a d s. o) showed that Δ H a d s. o and Δ G a d s. o are negative, while Δ S a d s. o was positive. The formation of a protective layer adsorbed on the surfaces of the substrates was confirmed with the surface analysis (SEM). The porosity percentage is significantly reduced in the inhibitor presence and gradually decreased with increasing concentration. Furthermore, the density functional theory (DFT) and Monte Carlo (MC) simulations were employed to explain the variance in protecting the Al surface from corrosion. Interestingly, the theoretical findings align with their experimental counterparts. The planarity of 2-MBT and the presence of heteroatoms are the playmakers in the adsorption process. [ABSTRACT FROM AUTHOR]

The benzothiadiazole/hexylthiophene, benzothiadiazole/hexylthiophene/N–hexylphenothiazine, benzothiadiazole/N-hexylphenothiazine alternating π-conjugated copolymers were synthesized via Pd-catalyzed cross-coupling reaction. The main structural differences among the three copolymers are the type of donor moiety (hexylthiophene and/or hexylphenothiazine). The polymer structures and photophysical properties were characterized by 1H NMR, 13C NMR, GPC, TGA, DSC, UV–vis absorption spectroscopy, PL spectroscopy, CV, and XRD measurement. The work is aimed at exploring the structural factors that could control the photophysical properties of copolymers in order to help in the rational design of polymers having specific physical properties used in optoelectronic devices. XRD of all copolymers showed a d-spacing range of 4.04 ~ 3.91 Å, reflecting the π-π stacking and some degree of crystallinity in their structure. Their PL spectra showed red and near infrared light, which nominates them as potential red and near infrared light-emitting materials for PLEDs. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations were employed in an attempt to supplement and explained the experimental measurement. The preliminary photovoltaic prediction of the studied copolymers was also reported. [ABSTRACT FROM AUTHOR]

Electronic interactions between the cationic N,N′-bis(2(trimethylammonium iodide) ethylene)perylene-3,4,9,10-tetracarboxyldiimide (TAIPDI) with two electron donors, namely, pyrene (Py) and 1-pyrenesulfonic acid sodium salt (PySA), have been investigated. The spectroscopic studies showed the formation of the supramolecular conjugate between TAIPDI and PySA via ionic interaction, but not with Py. Density functional theory (DFT) combined with a natural energy decomposition analysis (NEDA) technique showed an S-like structure of the supramolecular conjugate TAIPDI–PySA via an ionic interaction. The formation constant of the TAIPDI–PySA supramolecular conjugate was determined to be 3.0 × 104 M−1, suggesting a fairly stable complex formation. The excited state events were monitored by both steady state and time-resolved emission techniques. Upon excitation, the quenching pathways via the singlet-excited states of TAIPDI and PySA involved the intramolecular electron transfer from the electron donating PySA to the electron accepting TAIPDI with a rate constant of 1.10 × 1011 s−1 and a quantum yield of 0.99. The thermodynamic parameters of the supramolecular TAIPDI–PySA conjugate have been determined using the stopped-flow technique. [ABSTRACT FROM AUTHOR]

The effect of ring size on the photophysics and photochemistry of styrylbenzothiazole has been investigated via systematic replacement of the phenyl ring of 1-phenyl-2-(2-benzothiazolyl)ethene with naphthyl and phenanthryl rings. Steady state absorption and fluorescence techniques have been employed to record the spectra in a variety of solvents, in conjunction with density functional theory (DFT) calculations, to probe absorption spectra and other properties of relevance to photo-excitation. Important experimental parameters were determined, such as fluorescence quantum yield and quantum yields of photochemical E–Z isomerisation. In addition, the computed potential energy surfaces of the ground and excited states were constructed using DFT/TD-DFT methods that showed that the photo-reaction is based on an adiabatic mechanism, in the sense that the reaction occurs via the excited-state potential energy surface. Based on the significant blue shift of the Z-isomer absorption maximum relative to that of the E-isomer, and the high percentage of Z-isomers in the photo-stationary state, these compounds may serve as potential promising candidates for optical data storage applications. [ABSTRACT FROM AUTHOR]