Organic Semiconductors and Conductors with tert-Butyl Substituents

Innovative Implementation of an Alternative Tetrathiafulvene Derivative for Flexible Indium Phthalocyanine Chloride-Based Solar Cells

Herein, we present the photovoltaic properties of an indium phthalocyanine chloride (InClPc)-based flexible planar heterojunction device, introducing the tetrathiafulvene derivative 4,4′-Dimethyl-5,5′-diphenyltetrathiafulvalene (DMDP-TTF) as the electron donor layer. UV-vis spectroscopy is widely used to characterize the electronic behavior of the InClPc/DMDP-TTF active layer. The interactions between the DMDP-TTF and phthalocyanine are predominantly intermolecular and the result of the aggregation of InClPc. Tauc bands were obtained at 1.41 and 2.8 eV; these energy peaks can result in a charge transfer ascribed to the transition from the DMDP-TTF to π-orbitals that are associated with the phthalocyanine ring or even with the same indium metal center. Conductive carbon (CC) was used for the cathode. Finally, an indium tin oxide (ITO)/InClPc/DMDP-TTF/CC device was fabricated by high-vacuum thermal evaporation onto a flexible substrate and the photovoltaic properties were evaluated. A diode type I-V curve behavior was observed with a photovoltaic response under illumination. A generated photocurrent of 2.25 × 10⁻² A/cm² was measured. A conductivity reduction with the incident photon energy from 1.61 × 10⁻⁷ S/cm to 1.43 × 10⁻⁷ S/cm is observed. The diode resistance presents two different behaviors with the applied voltage. A V_TFL of 5.39 V, trap concentration of 7.74 × 10¹⁶ cm⁻³, and carrier mobility values of ~10⁻⁶ cm²/V s were calculated, showing improved characteristics via the innovative implementation of an alternative TTF-derivative, indicating that the DMDP-TTF has a strong interaction at the junction where free available states are increased, thus inducing higher mobilities due to the large number of π-orbitals, which indicates the feasibility of its use in solar cells technology.

Synthesis of Diaminopyrimidine Sulfonate Derivatives and Exploration of Their Structural and Quantum Chemical Insights via SC-XRD and the DFT Approach

Two heterocyclic compounds named 2,6-diaminopyrimidin-4-ylnaphthalene-2-sulfonate (A) and 2,6-diaminopyrimidin-4-yl4-methylbenzene sulfonate (B) were synthesized. The structures of heterocyclic molecules were established by the X-ray crystallographic technique, which showed several noncovalent interactions as N···H···N, N···H···O, and C-H···O bonding and parallel offset stacking interaction. Hydrogen-bonding interactions were further explored by the Hirshfeld surface (HS) analysis. Nonlinear optical (NLO) and natural bond orbital (NBO) properties were calculated utilizing the B3LYP/6-311G(d,p) level. Frontier molecular orbitals (FMOs) and molecular electrostatic potential (MEP) were calculated utilizing the time-dependent density functional theory (TD-DFT) at the same level. The NBO analysis showed that the molecular stabilities of compounds A and B were attributed to their large stabilization energy values. The second hyperpolarizability (γ_tot) values for A and B were obtained as 3.7 × 10⁴ and 2.7 × 10⁴ au, respectively. The experimental X-ray crystallographic and theoretical structural parameters of A and B were found to be in close correspondence. Both the molecules reveal substantial NLO responses that can be significant for their utilization in advanced applications.

The Stoichiometry of TCNQ-Based Organic Charge-Transfer Cocrystals

Organic charge-transfer cocrystals (CTCs) have attracted significant research attention due to their wide range of potential applications in organic optoelectronic devices, organic magnetic devices, organic energy devices, pharmaceutical industry, etc. The physical properties of organic charge transfer cocrystals can be tuned not only by changing the donor and acceptor molecules, but also by varying the stoichiometry between the donor and the acceptor. However, the importance of the stoichiometry on tuning the properties of CTCs has still been underestimated. In this review, single-crystal growth methods of organic CTCs with different stoichiometries are first introduced, and their physical properties, including the degree of charge transfer, electrical conductivity, and field-effect mobility, are then discussed. Finally, a perspective of this research direction is provided to give the readers a general understanding of the concept.

Green Synthesis, SC-XRD, Non-Covalent Interactive Potential and Electronic Communication via DFT Exploration of Pyridine-Based Hydrazone

Ultrasound-based synthesis at room temperature produces valuable compounds greener and safer than most other methods. This study presents the sonochemical fabrication and characterization of a pyridine-based halogenated hydrazone, (E)-2-((6-chloropyridin-2-yl)oxy)-N′-(2-hydroxybenzylidene) acetohydrazide (HBPAH). The NMR spectroscopic technique was used to determine the structure, while SC-XRD confirmed its crystalline nature. Our structural studies revealed that strong, inter-molecular attractive forces stabilize this crystalline organic compound. Moreover, the compound was optimized at the B3LYP/6-311G(d,p) level using the Crystallographic Information File (CIF). Natural bonding orbital (NBO) and natural population analysis (NPA) were performed at the same level using optimized geometry. Time-dependent density functional theory (DFT) was performed at the B3LYP/6-311G (d,p) method to calculate the frontier molecular orbitals (FMOs) and molecular electrostatic potential (MEP). The global reactivity descriptors were determined using HOMO and LUMO energy gaps. Theoretical calculations based on the Quantum Theory of Atoms in Molecules (QT-AIM) and Hirshfeld analyses identified the non-covalent and covalent interactions of the HBPAH compound. Consequently, QT-AIM and Hirshfeld analyses agree with experimental results.

Large Area Free-Standing Single Crystalline Films of p-Quinquephenyl: Growth, Structure and Photoluminescence Properties

Studies of the growth of large-area free-standing single-crystalline films of p-quinquephenyl are presented. High-quality crystals were grown by slow cooling of a hot chlorobenzene solution. Worse quality large-area free-standing single crystals of p-quinquephenyl were also grown by using physical vapor transport and used for comparison. The crystal structure of p-quinquephenyl at 293 K and 85 K was refined by single-crystal X-ray diffraction. The optical absorption and photoluminescence spectra of solutions and crystalline films were obtained and analyzed; a positive solvatochromic effect was detected.

Architecting layered molecular packing in substituted benzobisbenzothiophene (BBBT) semiconductor crystals

The construction of layered molecular packing structures in a non-layered crystalline material, benzobisbenzothiophene (BBBT), was achieved by employing long-alkyl and phenyl substituents, leading to high-performance organic thin-film transistors.

Electronic engineering of a tetrathiafulvalene charge-transfer salt via reduced symmetry induced by combined substituents

A 1 : 1 metallic charge-transfer salt is obtained by cosublimation of (Z,E)-(SMe)2Me2TTF and TCNQ. X-ray diffraction studies confirm the formation of segregated stacks comprising donor and acceptor molecules in [(E)-(SMe)2Me2TTF](TCNQ). The crystal packing features lateral SS interactions between TTF stacks, which is in sharp contrast to that in (TTF)(TCNQ). Structural analysis and theoretical studies afford a partial charge-transfer (ρ ≈ 0.52), leading to a system with the electronic structure close to quarter-filled. Resistivity measurements reveal that this material behaves as a metal down to 56 K and 22 K at 1 bar and 14.9 kbar, respectively. The thermopower is negative in the metallic regime, indicating the dominant role of the acceptor stacks for the observed conducting behavior. Analysis of single-crystal EPR spectra shows the remaining spin susceptibility at 4.3 K, suggesting the importance of the Hubbard U correction. These results highlight the judicious engineering of electronic and geometrical effects on the TTF core; the combined use of methyl and thiomethyl groups has decreased the TCNQ bandwidth while maintaining the segregated stacks, converting the metal to insulator (M-I) transition to more 4kF like. In addition, the enhanced SS contacts between the TTF stacks lead to more rapidly decreasing M-I transition temperature under various pressures.

Gold and Nickel Extended Thiophenic-TTF Bisdithiolene Complexes

Gold and nickel bisdithiolene complexes with methyl and tert-butyl substituted thiophenetetrathiafulavalenedithiolate ligands (α-mtdt and α-tbtdt) were prepared and characterized. These complexes were obtained, under anaerobic conditions, as tetrabutylammonium salts. The diamagnetic gold monoanion (n-Bu₄N)[Au(α-mtdt)₂] (3) and nickel dianionic species (n-Bu₄N)_x[Ni(α-mtdt)₂] (x = 1,2) (4) were similar to the related non-substituted extended thiophenic-TTF (TTF = tetrathiafulvalene) bisdithiolenes. However the introduction of the large, bulky substituent tert-butyl, led to the formation of a Au (I) dinuclear complex, (n-Bu₄N)₂[Au₂(α-tbtdt)₂] (5). The neutral methyl substituted gold and nickel complexes were easily obtained through air or iodine exposure as polycrystalline or amorphous fine powder. [Au(α-mtdt)₂] (6) and [Ni(α-mtdt)₂] (7) polycrystalline samples display properties of a metallic system with a room temperature electrical conductivity of 0.32 S/cm and ≈4 S/cm and a thermoelectric power of ≈5 µV/K and ≈32 µV/K, respectively. While [Au(α-mtdt)₂] (6) presented a Pauli-like magnetic susceptibility typical of conducting systems, in [Ni(α-mtdt)₂] (7) large magnetic susceptibilities indicative of high spin states were observed. Both electric transport properties and magnetic properties for gold and nickel [M(α-mtdt)₂] are indicative that these compounds are single component molecular conductors.

Single-Component Conductors: A Sturdy Electronic Structure Generated by Bulky Substituents

While the introduction of large, bulky substituents such as tert-butyl, -SiMe3, or -Si(isopropyl)3 has been used recently to control the solid state structures and charge mobility of organic semiconductors, this crystal engineering strategy is usually avoided in molecular metals where a maximized overlap is sought. In order to investigate such steric effects in single component conductors, the ethyl group of the known [Au(Et-thiazdt)2] radical complex has been replaced by an isopropyl one to give a novel single component molecular conductor denoted [Au(iPr-thiazdt)2] (iPr-thiazdt: N-isopropyl-1,3-thiazoline-2-thione-4,5-dithiolate). It exhibits a very original stacked structure of crisscross molecules interacting laterally to give a truly three-dimensional network. This system is weakly conducting at ambient pressure (5 S·cm(-1)), and both transport and optical measurements evidence a slowly decreasing energy gap under applied pressure with a regime change around 1.5 GPa. In contrast with other conducting systems amenable to a metallic state under physical or chemical pressure, the Mott insulating state is stable here up to 4 GPa, a consequence of its peculiar electronic structure.

Correlating conduction properties with the molecular symmetry: segregation of Z and E isomers in the charge-assisted, halogen-bonded cocrystal [(Z,E)-Me2I2TTF]2Br

Co-crystallization of theZandEisomers of Me₂I₂TTF in a mixed-valence bromide salt leads to segregated stacks with two different charge order patterns and associated charge-assisted halogen bonding.

Gold dithiolene complexes: easy access to 2-alkylthio-thiazoledithiolate complexes

In the presence of MeI or EtI, N-tert-butyl-1,3-thiazoline-2-thione derivatives undergo a transformation to 2-alkylthio-thiazoledithiolate pro-ligands with elimination of the tert-butyl substituent. The corresponding Au(III) dithiolene complexes [Au(RS-tzdt)2](-) (R = Me, Et) oxidize readily to the neutral radical species, such as the semi-conducting [Au(EtS-tzdt)2]˙, which organizes into dimers in the solid state.