Synthesis and Strong π-π Interaction of Hexaazatriphenylene Derivatives with Alternating Electron-Withdrawing and -Donating Groups.

Introduction: The development of sustainable energy systems critically depends on efficient hydrogen storage materials. Conventional physisorption frameworks, such as MOFs and COFs, are constrained by weak binding energies and limited tunability, necessitating new molecular platforms with superior adsorption characteristics. Methods: We employed density functional theory (DFT) calculations with dispersion corrections to investigate the strategic functionalization of 2D hexaazatriphenylene (HAT), a nitrogen-rich, π- conjugated macrocycle, as a next-generation hydrogen storage platform. Various substituents, including electron-donating (−Bpin, −OH), electron-withdrawing (−NO2, −COH), and ambiphilic (−SF5, −SO3H) groups, were systematically incorporated to modulate adsorption properties. Results: Our findings reveal that functionalized HAT derivatives synergize van der Waals interactions, quadrupole coupling, and substituent-induced polarization, achieving hydrogen binding energies of up to −8.6 kJ·mol?¹, approaching the U.S. DOE target of 15 kJ·mol?¹ for physisorption-based materials. The HAT-PB (−Bpin) derivative exhibited optimal non-dissociative physisorption, maintaining an H–H bond length of 0.74 Å, minimal charge transfer (−0.041 e), and tunable HOMOLUMO gaps (6.4–7.2 eV). Discussion: This work closes a significant research gap by presenting the first systematic study of HAT derivatives for hydrogen storage. The nitrogen-enriched core of HAT enhances charge localization, while substituent engineering provides precise control over adsorption energy and reversibility. Conclusion: Our computational insights establish functionalized HAT frameworks as promising candidates for reversible hydrogen storage, offering a design blueprint that could accelerate the development of lightweight, high-capacity energy materials.

Synthesis and spectral properties of new fluorescent alkoxy-substituted thieno[3,2-b]indole derivatives

Five different alkenylgold(I) phosphane complexes were prepared and then investigated in [1,1′‐bis(diphenylphosphino)ferrocene]palladium(II) dichloride‐catalyzed cross‐coupling reactions with different aryl halides, heterocyclic halides, an alkenyl halide, an alkynyl halide, allylic substrates, benzyl bromide and an acid chloride. With regard to the halides, the iodides were highly reactive, bromides or chlorides gave significantly reduced yields or failed, allylic acetates failed, too. The cross‐coupling partners contained a number of different functional groups, while free carboxylic acids did not deliver cross‐coupling products and o,o‐disubstituted arenes failed as well, a broad range of other functional groups like nitro groups, nitrile groups, ester groups, α,β‐unsaturated ester groups and lactones, aldehydes, alkoxy groups, pyridyl groups, thienyl groups, unprotected phenols and anilines, even aryl azides were tolerated. The structures of one alkenylgold(I) species and of four of the cross‐coupling products were proved by crystal structure analyses.

Charge carrier mobility is an important primary parameter for the electronic conductive materials, and the intrinsic limit of the mobility has been hardly access by conventional direct-current evaluation methods. In the present study, intra-grain hole mobility of pentacene thin films was estimated quantitatively using microwave-based dielectric loss spectroscopy (time-resolved microwave conductivity measurement) in alternating current mode of charge carrier local motion. Metal-insulator-semiconductor devices were prepared with different insulating polymers or substrate temperature upon vacuum deposition of the pentacene layer, which afforded totally four different grain-size conditions of pentacene layers. Under the condition where the local motion was determined by interfacial traps at the pentacene grain boundaries (grain-grain interfaces), the observed hole mobilities were plotted against the grain sizes, giving an excellent correlation fit successfully by a parabolic function representative of the boarder length. Consequently, the intra-grain mobility and trap-release time of holes were estimated as 15 cm2 V−1 s−1 and 9.4 ps.

To study the mobility and lifetime of charge carriers in thin film polycrystalline silicon deposited by hot-wire chemical vapor deposition, time-resolved microwave conductivity measurements have been performed. Using this technique the change in conductivity in the polycrystalline silicon films after pulsed excitation can be monitored on a nanosecond time scale, without the use of electrodes. Due to the different penetration depths of the laser wavelengths used (320, 500, and 690 nm) combined with illumination from different sides, the photoconductivity in different regions within the sample can be measured. Four different samples of polycrystalline silicon deposited on Corning glass have been studied: Poly1 (highly defective), Poly2 (device quality) and profiled layers of Poly1 and Poly2. For front or back illumination, the conductivity transients for the Poly1 film are very similar and show that lifetimes of the charge carriers generated are less than 1 ns. For the Poly2 film the mobility in the interfacial substrate region (μ=0.17 cm2/V s) is more than 1 order of magnitude lower than in the top region (μ=3.8 cm2/V s). The formation of a thin Poly1 film on the surface of the Corning substrate, acting as a seed layer for the Poly2 layer, followed by the deposition of the Poly2 layer, results in only a relatively small increase in the mobility in the region close to the substrate as compared to the bare Poly2 layer, while the mobility in the top region remains approximately constant.

Carrier multiplication-the generation of multiple electron-hole pairs by a single photon-is currently of great interest for the development of highly efficient photovoltaics. We study the effects of infilling PbSe quantum-dot solids with metal oxides by atomic layer deposition on carrier multiplication. Using time-resolved microwave conductivity measurements, we find, for the first time, that carrier multiplication occurs in 1,2-ethanedithiol-linked PbSe quantum-dot solids infilled with Al2O3 or Al2O3/ZnO, while it is negligible or absent in noninfilled films. The carrier-multiplication efficiency of the infilled quantum-dot solids is close to that of solution-dispersed PbSe quantum dots, and not significantly limited by Auger recombination.

To further understand the optoelectronic properties of metal halide perovskites, we investigate sub-bandgap absorption in methylammonium lead iodide (MAPbI3) films. Charge carrier dynamics are studied using time-resolved microwave conductivity measurements using sub-bandgap excitation. From changes in the decay dynamics as a function of excitation energy and intensity, we have identified three regimes: (i) Band-like charge transport at photon energies above 1.48 eV; (ii) a transitional regime between 1.48 and 1.40 eV; and (iii) below 1.40 eV localized optically active defects (8 × 1013 cm-3) dominate the absorption at low intensities, while two-photon absorption is observed at high intensities. We determined an Urbach energy of approximately 11.3 meV, indicative of a low structural and/or thermal disorder. Surprisingly, even excitation 120 meV below the bandgap leads to efficient charge transfer into electron (C60) or hole (spiro-OMeTAD) transport layers. Therefore, we conclude that for MAPbI3, the band tail states do not lead to nonradiative losses.

Transient photoconductivity measurements have been performed in situ during plasma-enhanced chemical vapor deposition of amorphous hydrogenated silicon by a contactless method that uses the change of the microwave reflection after laser pulse illumination. Through the use of the interference pattern of the amplitude of the transients of microwave reflection during the layer growth, the actual thickness of the amorphous film can be determined. In the case of crystalline silicon substrates, the change in the light absorption in the substrate modified by the growth of the amorphous layer is measured directly. An example of the optimization of antireflective layers on crystalline silicon substrates is shown. A good agreement is found between the experimental data and calculations of optical reflection and transmission on the multilayer structures.

Tin disulfide (SnS2) is a two-dimensional semiconducting van der Waals material with an indirect band gap. We measured the mobility and recombination dynamics of charge carriers as a function of temperature and charge density. Excess electrons and holes were generated by pulsed irradiation with 3 MeV electrons. The charge carriers were probed by time-resolved microwave conductivity measurements. The mobility and decay pathways of the charge carriers were determined by a global kinetic rate equation model including decay of charges by recombination and trapping. We found high mobilities for electrons and holes near 100 cm2 V–1 s–1. The mobility decreases at higher temperature, which is typical for bandlike transport. The second-order recombination rate constant is found to be thermally activated with an activation energy close to the energy difference of the direct and indirect band gap of SnS2. We demonstrate that the radiative recombination is reaction-limited and takes place via the Γ-point after thermal excitation of electrons from the M-point to the Γ-point, while a phonon emission-related recombination between the indirect band gap (M-point electrons and Γ-point holes) has no relevant contribution to the population decay. The observed effects result in an unusual increase of radiative electron–hole recombination constant with temperature.

We have studied the real and imaginary parts of the complex intrachain mobility of charge carriers on solid samples of ladder-type polymers using time-resolved microwave conductivity measurements. Experiments on samples with a different average polymer chain length show that the motion of charge carriers is limited by the chain ends. The experimental results can be described by one-dimensional diffusive motion along the polymer backbone. The intrachain mobility deduced for an infinitely long ladder-type polymer chain (with no barriers to charge transport such as defects or conjugation breaks) subject to interchain interactions is $30\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{2}∕\mathrm{V}\phantom{\rule{0.2em}{0ex}}\mathrm{s}$. This value is 20 times lower than the intrachain mobility found for charges along infinitely long isolated ladder-type polymer chains in dilute solution. Thus we find that interchain interactions in solid samples severely decrease the intrachain charge carrier mobility. However, the intrachain mobility of $30\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{2}∕\mathrm{V}\phantom{\rule{0.2em}{0ex}}\mathrm{s}$ is more than four orders of magnitude higher than mobility values obtained from time of flight measurements reported in the literature. Hence, the performance of ladder-type polymers in optoelectronic devices can be significantly improved.

Organic semiconductors have revolutionized electronics, but their amorphous nature hinders performance and stability. Crystallinity overcomes these limitations; however, the design of materials that combine high crystallinity, optimal thermal properties, and ease of synthesis remains a significant challenge. A machine learning (ML)‐assisted approach combined with the density functional theory (DFT) study was employed to generate a vast chemical space of crystallizable organic semiconductors. By breaking retrosynthetically interesting chemical species (BRICS), over 1700 new organic semiconductors with promising synthetic accessibility (SA) were designed. ML algorithms, specifically extra trees (ET) and random forest, were used to predict the melting temperatures ( T m ) of these semiconductors, yielding good R ‐squared ( R 2 ) values of 0.94–0.96. Dimensionality reduction analysis reveals that the t‐distributed stochastic neighbor embedding (t‐SNE) components 1 and 2 of these semiconductors ranged within the same value (−5 to 5), indicating a high degree of similarity. Furthermore, analysis of SA showed that new organic semiconductors with SMILES lengths between 15 and 40 are more likely to be easily synthesized. Based on these findings, 20 new candidate semiconductors were identified for practical synthesis and analysis. DFT calculations were employed to study the optoelectronic properties of chromophores. This study demonstrates the power of ML‐assisted design in generating crystallizable organic semiconductors with enhanced SA. The findings are expected to contribute significantly to the development of high‐performance organic electronics.

The field of synthetic metals is, and remains, highly influential for the development of organic semiconductor materials. Yet, with the passing of time and the rapid development of conjugated materials in recent years, the link between synthetic metals and organic semiconductors is at risk of being forgotten. This review reflectson one of the key concepts developed in synthetic metals - heteroatom interactions. The application of this strategy in recent organic semiconductor materials, small molecules and polymers, is highlighted, with analysis of X-ray crystal structures and comparisons with model systems used to determine the influence of these non-covalent short contacts. The case is made that the wide range of effective heteroatom interactions and the high performance that has been achieved in devices from organic solar cells to transistors is testament to the seeds sown by the synthetic metals research community.

Mechanochemical fabrication of Se-doped poly(triazine imide) with donor-acceptor motifs for photocatalytic cleavage of C-C bonds in lignin.

A theoretical approach for simulations of anisotropic charge carrier mobility in organic single crystal semiconductors

Organic semiconductors (OSCs) have garnered significant attention due to their potential use in flexible, lightweight, and cost‐effective electronic devices. Despite their promise, the assembly of organic molecules into the condensed phase promotes a diverse set of lattice dynamics that introduce a detrimental modulation in the intermolecular electronic structure—termed dynamic disorder—that results in charge carrier mobilities that are orders of magnitude lower than inorganic semiconductors. This dynamic disorder is generally associated with low‐frequency phonons, yet whether a small subset of modes or a broad range of phonons drives dynamic disorder remains contested. Resolving this debate is critical for defining how targeted phonon engineering could practically improve OSC performance. In this review, we explore progress toward uncovering the interplay between lattice dynamics and charge transport in OSCs, focusing on the critical role of thermally activated phonons. We describe the powerful insight that mode‐resolved analyses of electron–phonon interactions lends toward the rational design of new materials. We highlight recent efforts to achieve this, showcasing proposed strategies to mitigate dynamic disorder through molecular and crystal design. This work offers an overview of the insight gained toward understanding the fundamental mechanisms governing charge transport in OSCs and outlines pathways for enhancing performance via targeted manipulation of interatomic/intermolecular interactions and resulting phonon modes.