Modified Donor End Caps for Binary-to-Ternary WORM Memory Conversion in N-Heteroaromatic Systems

A series of novel D-π-A type organic small molecules have been designed, synthesized, and demonstrated for non-volatile resistive switching WORM memory application. The electron-deficient phenazine and quinoxaline units were coupled with various functionalized triphenylamine end caps to explore the structure-property correlations. The photophysical investigations displayed considerable intramolecular charge transfer, and the electrochemical analysis revealed an optimum band gap of 2.44 to 2.83 eV. These factors and the thin film morphological studies suggest the feasibility of the compounds as better resistive memory devices. All the compounds indicated potent non-volatile resistive switching memory capabilities with ON/OFF ratios ranging from 103 to 104, and the lowest threshold voltage recorded stands at -0.74 V. A longer retention time of 103 s marks the substantial stability of the devices. The phenazine-based compounds outperformed the others in terms of memory performance. Exceptionally, the compound with -CHO substituted triphenylamine exhibited ternary memory performance owing to its multiple traps. The resistive switching mechanism for the devices was validated using density functional theory calculations, which revealed that the integrated effect of charge transfer and charge trapping contributes significantly to the resistive switching phenomena.

A direct entry to polycyclic quinoxaline derivatives via I2-DMSO mediated oxidative decarboxylation of α-amino acids and the subsequent Pictet-Spengler cyclization reaction

A facile and highly efficient iodine-promoted strategy has been delineated for the synthesis of indolo and pyrrolo[1,2-a]quinoxaline derivatives via an oxidative Pictet-Spengler type amino cyclo-annulation reaction using ∝-amino acids as aldehyde surrogates. The concomitant benzylic oxidation and the compatibility of different starting materials under standard conditions made the current method versatile. The salient features of the protocol such as readily available starting materials, inexpensive promoters, environmental benignity, broad substrate scope, scalability, and good to excellent yield make the method more attractive to practitioners of organic synthesis.

LC-BLYP Calculations of the Structures and Photophysical Properties of [1,3]Thiazolo[4,5-b]pyrazine Derivatives in Cyclohexane and Methanol

Applications of the B3LYP and LC-BLYP functionals with the 6-311+G(d,p) basis set for predicting absorption and fluorescence spectra of benzothiazole and 11 [1,3]thiazolo[4,5-b]pyrazine (TPy) derivatives in implicit solvents (cyclohexane and methanol) were tested and compared with experimental results. The damping parameter of LC-BLYP was tuned for simulating absorption and fluorescence spectra of each compound. For the 11 TPy derivatives, four and seven compounds are small- and medium-sized TPy derivatives, respectively. From this calculation, TD-B3LYP can be used to simulate the absorption spectra of the small-sized compounds in cyclohexane and methanol, but it gives poor results for the fluorescence spectra in cyclohexane and methanol. Contrarily, the LC-BLYP functional with the optimal damping parameter can reproduce the absorption and fluorescence spectra of all compounds in cyclohexane and methanol. The values of the damping parameter of LC-BLYP depend on the types of substituents and solvents. Moreover, the conformations of the compounds do not affect the spectra, and the molecular size and molecular dipole moment do not affect the damping parameter. In addition, types and the number of substitutions attached to the phenyl rings of TPy as well as solvent polarity play the key roles in the long-wavelength fluorescence emission and fluorescence brightness of the compounds. The intramolecular charge transfer of the compounds containing the -NMe₂ and -CN groups is predominant in methanol, resulting in a large Stokes shift and oscillator strength.

Theoretical study on the electronic structure and second-order nonlinear optical properties of benzannulated or selenophene-annulated expanded helicenes

Currently, discovering new materials with superior second-order nonlinear optical (NLO) performance has become a very hot research topic in the fields of chemistry and materials science. Now, density functional theory (DFT) has become a powerful tool to predict the performance of novel materials. In this paper, based on benzannulated and selenophene-annulated expanded helicenes, twenty-six helicenes are designed by introduction donor/acceptor moieties and their combinations at different substituent positions. The geometrical/electronic structures, electronic transition, and second-order NLO properties of these helicenes are full investigated by DFT/TDDFT theory. The investigations show that these helicenes have large first hyperpolarizability values (β HRS). For instance, the β HRS value (29.95 × 10-30 esu) of helicene H24 is about 7 times larger than that of the highly π-delocalized phenyliminomethyl ferrocene complex. In addition, the introduction of acceptor NO2 unit at R7 and R8 positions for helicenes H1 and H15 can obtain the largest β HRS value, which is attributed to the enhancement of electron acceptor ability. In view of large NLO response and intrinsic asymmetric structures, the studied helicenes have the possibility to be excellent second-order NLO materials.

Electronic and Vibrational Hyperpolarizabilities of Lithium Substituted (Aza)benzenes and (Aza)naphthalenes

In this article we report results for the electronic and vibrational hyperpolarizabilities of ten molecules: Li@benzene, Li@pyridine, Li@pyrimidine, and Li@pyrazine; Li@naphthalene, Li@quinoline, Li@isoquinoline, Li@cinnolin, Li@quinazoline, and Li@quinoxaline. An electron correlation study shows that second-order many-body perturbation theory and density functional theory with CAM-B3LYP and M05-2X functionals give results for the electronic hyperpolarizabilities in good agreement with coupled cluster with single and doubles reference values. Static and dynamic vibrational corrections were computed through the perturbation theoretical method of Bishop and Kirtman and using a variational approach. In general, we obtained notable discrepancies between the results obtained by the two methods for the pure vibrational corrections because of the deficiency of the perturbation method to properly treat low-frequency normal modes present in the investigated systems. However, both methods give results similar to the zero-point vibrational average corrections.

Theoretical study on thiophene-based double helicenes with intrinsic large second-order nonlinear optical response

In view of the intrinsic non-centrosymmetric electronic structures, high transparency, and the large second-order NLO response values, the studied thiophene-based double helicenes are expected to be excellent second-order NLO materials.

Understanding the photophysical properties of chiral dinuclear Re(i) complexes and the role of Re(i) in their complexes

We have investigated the electronic structure, UV-Vis/CD spectra and the second-order NLO properties of chiral dinuclear Re(i) complexes and elucidated structure–property relationships with the aid of DFT calculations.