Optoelectronic and nonlinear optical properties of triarylamine helicenes: a DFT study

Giant NLO response and deep ultraviolet transparency of dual (alkali/alkaline earth) metals doped C6O6Li6 electrides

The designing of new materials having outstanding nonlinear optical (NLO) response is much needed for use in latest optics. Herein, the geometric, electronic and NLO properties of alkali and alkaline earth metals doped C6O6Li6 (alk-C6O6Li6-alkearth, alkearth = Ca, Mg, Be and alk = K, Na, Li) electrides is studied via quantum chemical approach. The interaction energies (Eint) are examined to illustrate their thermodynamic stability. The strong interaction energy of -39.99 kcal mol-1 is observed for Ca-C6O6Li6-Li electride in comparison to others. Frontier molecular orbitals (FMOs) energy gap of considered complexes is changed due to the electronic density shifting between metals and C6O6Li6 surface, which notifies the semi conducting properties of these electrides. The FMOs isodensities and natural bond orbital (NBO) charge analysis are performed to justify charge transfer between dopants and complexant. UV-Visible study also confirmed the application of these electrides as deep ultra-violet laser devices. NLO response is studied through calculation of first hyperpolarizability (βo). The highest βo value of 1.68 × 105 au is calculated for Mg-C6O6Li6-K electride. NLO response is further rationalized by three- and two-level models approach.

Azatriseptanes: Strained Framework Analogs of [7,7,7]Circulenes

The synthesis and characterization of heptagon-embedded polycyclic aromatic compounds are essential for understanding the effect of negative curvature on carbon allotropes such as fullerenes and graphenes that have applications in functional organic materials. However, owing to the synthetic difficulties in functionalizing and embedding seven-membered rings, these strain-challenged structures are relatively unexplored. We report here the synthesis, characterization, and properties of a triarylamine core bridged with ethano chains at the 2,2'-positions. In doing so, we provide access to the first heterocycle containing three fused heptagon rings with a nitrogen at its core (BATA-NHAc). X-ray crystallographic analysis and DFT calculations revealed a remarkably strained structure wherein two of the bridged aryl units approach coplanarity, while the third ring is twisted out of plane at 70°. UV-vis and emission spectroscopies identify red-shifted absorption and concentration-dependent emission profiles, respectively, as a result of the unique conformation and self-assembly properties of BATA-NHAc. Furthermore, cyclic voltammetry shows a decrease in the oxidation potential for BATA-NHAc in comparison to the non-bridged analog. This study opens new avenues in understanding the structure-property relationships of curved π-aromatics and the construction of π-frameworks of increasing complexity.

Demonstrating the Potential of Alkali Metal-Doped Cyclic C6O6Li6 Organometallics as Electrides and High-Performance NLO Materials

In this report, the geometric and electronic properties and static and dynamic hyperpolarizabilities of alkali metal-doped C6O6Li6 organometallics are analyzed via density functional theory methods. The thermal stability of the considered complexes is examined through interaction energy (E int) calculations. Doping of alkali metal derives diffuse excess electrons, which generate the electride characteristics in the respective systems (electrons@complexant, e-@M@C6O6Li6, M = Li, Na, and K). The electronic density shifting is also supported by natural bond orbital charge analysis. These electrides are further investigated for their nonlinear optical (NLO) responses through static and dynamic hyperpolarizability analyses. The potassium-doped C6O6Li6 (K@C6O6Li6) complex has high values of second- (βtot = 2.9 × 105 au) and third-order NLO responses (γtot = 1.6 × 108 au) along with a high refractive index at 1064 nm, indicating that the NLO response of the corresponding complex increases at a higher wavelength. UV-vis absorption analysis is used to confirm the electronic excitations, which occur from the metal toward C6O6Li6. We assume that these newly designed organometallic electrides can be used in optical and optoelectronic fields for achieving better second-harmonic-generation-based NLO materials.

In-Fjord Substitution in Expanded Helicenes: Effects of the Insert on the Inversion Barrier and Helical Pitch

A series of expanded helicenes of different sizes and shapes incorporating phenyl- and biphenyl-substituents at the deepest part of their fjord have been synthesized via sequential Au-catalyzed hydroarylation of appropriately designed diynes, and their racemization barriers have been calculated employing electronic structure methods. These show that the overall profile of the inversions (energies, number of transition states and intermediates, and their relative position) is intensively affected by the interplay of steric and attractive London dispersion interactions. Hence, in-fjord substitution constitutes an additional tool to handle the mechanical properties in helicenes of uncommonly large diameter. The photochemical characterization of the newly prepared helical structures is also reported.

Bacterial Antifouling Characteristics of Helicene-Graphene Films

Herein, we describe interfacially-assembled [7]helicene films that were deposited on graphene monolayer using the Langmuir-Schaefer deposition by utilizing the interactions of nonplanar (helicene) and planar (graphene) π–π interactions as functional antifouling coatings. Bacterial adhesion of Staphylococcus aureus on helicene—graphene films was noticeably lower than that on bare graphene, up to 96.8% reductions in bacterial adhesion. The promising bacterial antifouling characteristics of helicene films was attributed to the unique molecular geometry of helicene, i.e., nano-helix, which can hinder the nanoscale bacterial docking processes on a surface. We envision that helicene—graphene films may eventually be used as protective coatings against bacterial antifouling on the electronic components of clinical and biomedical devices.

Computational Studies on Optoelectronic and Nonlinear Properties of Octaphyrin Derivatives

The electronic and nonlinear optical (NLO) properties of octaphyrin derivatives were studied by employing the DFT/TDFT at CAM-B3LYP/6-311++G (2d, 2p) level of the theory. Thiophene, phenyl, methyl and cyano moieties were substituted on the molecular framework of octaphyrin core, in order to observe the change in optoelectronic and nonlinear response of these systems. The frontier molecular orbital studies and values of electron affinity reveals that the studied compounds are stable against the oxygen and moisture present in air. The calculated ionization energies, adiabatic electron affinity and reorganization energy values indicate that octaphyrin derivatives can be employed as effective n-type material for Organic Light Emitting Diodes (OLEDs). This character shows an enhancement with the introduction of an electron withdrawing group in the octaphyrin framework. The polarizability and hyperpolarizability values of octaphyrin derivatives demonstrate that they are good candidates for NLO devices. The nonlinear response of these systems shows enhancement on the introduction of electron donating groups on octaphyrin moiety. However, these claims needs further experimental verification.

Photophysical properties of quinoxaline-fused [7]carbohelicene derivatives

The electronic circular dichroism, UV-Vis absorption, nonlinear optics, and charge transport properties of novel quinoxaline-fused 7-carbohelicene derivatives have been investigated for the first time.