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Dianionic bis(propionate)-naphthalenediimide (PCNDI2–) formed simple 2:1 cation–anion salts of (M+)2(PCNDI2–)·(H2O)n(M+= Li+, Na+, K+, Rb+, and Cs+), which exhibited reversible H2O adsorption–desorption behavior because of the presence of their electrostatically binding crystal lattices. The maximum H2O adsorption amounts (n) for M+= Li+, Na+, K+, Rb+, and Cs+were 0.25, 6.0, 4.0, 6.0, and 2.0, respectively, whereas the reversible gate-opening (gate-closing) H2O adsorption–desorption isotherms were observed at 273 and 298 K, except for M+= Li+. High ionic conductivities of around 10–4–10–5S cm–1were observed in M+= Na+and K+salts, whereas short-range thermal fluctuations occurred in large cations of M+= Rb+and Cs+. The change in the electrostatic lattice energy for M+= Na+and K+salts during the H2O adsorption–desorption cycles was significantly larger than those for M+= Rb+and Cs+. Therefore, the Na+and K+salts had a considerably flexible electrostatic crystal lattice with a large amplitude of lattice modulation during the H2O sorption cycle. In contrast, the lattice modulation for M+= Rb+and Cs+salts involved a low magnitude of ion displacements, forming a relatively rigid cation–anion electrostatic crystal lattice. The flash-photolysis time-resolved microwave conductivity and transition absorption spectroscopy results revealed the high electron mobility of H2O-adsorbed thin films, wherein the crystallized H2O molecules did not act as electron-trapping sites. The values of electron mobility increased in the order of Cs+≈ Rb+> K+> Na+> Li+.

Polar H2O molecules generally act as trapping sites and suppress the electron mobility of n-type organic semiconductors, making chemical design of H2O-tolerant and responsive n-type semiconductors an important step toward multifunctional electron–ion coupling devices. The introduction of effective electrostatic interactions between potassium ions (K+) and carboxylate (−COO–) anions into the electron-transporting naphthalenediimide π-framework enables the design of high-performance H2O-tolerant n-type semiconductors with a reversible H2O adsorption–desorption ability, where the electron mobility and K+ionic conductivity were coupled with the reversible H2O sorption behavior. The reversible H2O adsorption into the crystals enhanced the electron mobility from 0.04 to 0.28 cm2V–1s–1, whereas the K+ionic conductivity decreased from 3.4 × 10–5to 4.7 × 10–7S cm–1. Because this reversible electron–ion conducting switch is responsive to H2O sorption behavior, it is a strong candidate for H2O gating carrier transport systems.

Herein, we report a novel porphyrin/fullerene supramolecular cocrystal using a shape-persistent zinc-metalated porphyrin box (Zn-PB) and C60/C70. An unprecedented arrangement of a tightly packed square-planar core of four C60or C70surrounded by six cube-shaped Zn-PBs was observed. This unique packing promotes strong charge transfer (CT) interactions between the two components in the ground state and formation of charge-separated states with very long lifetimes in the excited state and enables unusually high photoconductivity. Quantum chemical calculations show that these features are enabled by delocalized orbitals that promote the CT, on one hand, and that are spatially separated from each other, on the other hand. This work may open a new avenue to design novel electron donor/acceptor architectures for artificial photosynthesis.

Visible-light-driven hydrogen (H2) production from water is a promising strategy to convert and store solar energy as chemical energy. Covalent organic frameworks (COFs) are front runners among different classes of organic photocatalysts. The photocatalytic activity of COFs depends on numerous factors such as the electronic band gap, crystallinity, surface area, exciton migration, stability of transient species, charge separation and transport, etc. However, it is challenging to fine tune all of these factors simultaneously to enhance the photocatalytic activity. Hence, in this report, an effort has been made to understand the interplay of these factors and identify the key factors for efficient photocatalytic H2production through a structure–property–activity relationship. Careful molecular engineering allowed us to optimize all of the above plausible factors impacting the overall catalytic activities of a series of isoreticular COFs. The present study determines three prime factors: light absorption, charge carrier generation, and its transport, which influence the photocatalytic H2production of COFs to a much greater extent than the other factors.

We have developed the synthesis of 1,3,6,8-tetramethoxy-2,7-diazapyrene through reductive aromatization of naphthalene diimide. The methoxy groups were readily converted to a variety of alkyl groups through Ni-catalyzed cross-coupling reaction with alkyl Grignard reagents. The peripheral substituents significantly influenced the packing structures of 2,7-diazapyrenes in the solid state.We have developed the synthesis of 1,3,6,8-tetramethoxy-2,7-diazapyrene through reductive aromatization of naphthalene diimide. The methoxy groups were readily converted to a variety of alkyl groups through Ni-catalyzed cross-coupling reaction with alkyl Grignard reagents. The peripheral substituents significantly influenced the packing structures of 2,7-diazapyrenes in the solid state. While 1,3,6,8-tetraethyl-2,7-diazapyrene adopted a slipped stacking arrangement, the corresponding methyl analogue exhibited face-to-face columnar stacking in crystal. Furthermore, FI-TRMC measurements revealed the high electron mobility of 1,3,6,8-tetramethyl-2,7-diazapyrene.

Dianionic bis(benzenesulfonate)–naphthalenediimide (BSNDI2–) formed simple 2:1 cation–anion salts of (NH4+)2(BSNDI2–) (1), (CH3NH3+)2(BSNDI2–) (2), (C2H5NH3+)2(BSNDI2–) (3), [(C2H5)2NH2+]2(BSNDI2–) (4), and [(C2H5)3NH+]2(BSNDI2–) (5). The thermal stability, crystal structure, electron transport properties, and dielectric response were evaluated for these systems in terms of π-electron density and dimensional crossover from two-dimensional (2D) and one-dimensional (1D) to zero-dimensional (0D) electronic structures. Systematic modification of the counter cations from NH4+to simple alkylammoniums (CH3NH3+, C2H5NH3+, (C2H5)2NH2+, and (C2H5)3NH+) for BSNDI2–salts affected the packing π-density and dimensionality of NDIπ-cores. All single crystals formed alternating cation–anion layers, where the intermolecular interactions in salts 1, 2, 3, 4, and 5were observed as dense 2D brickstone, 1D column, 1D column, dilute 2D herringbone, and isolated 0D monomer arrangements, respectively. The π-electron occupation percentage in the unit cell of salts 1, 2, 3, 4, and 5decreased in that order, at 96.2%, 87.8%, 83.8%, 78.8%, and 72.6%, respectively, where the intermolecular π–π interaction between BSINDI2–anions was gradually diluted on increasing in the cation volume. The transfer integrals between the lowest unoccupied molecular orbital in salts 1–5clearly indicated a dimensional crossover from 2D to 1D to 0D electronic structures. Flash-photolysis time-resolved microwave conductivity measurements of salts 1, 2, 3, and 4helped determine the magnitude of electron carrier mobility, which followed the order 1> 2≈ 3≈ 4. The dielectric response of salt 1being an order of magnitude higher than those of salts 2–5was associated with the protonic conductivity in the NH4+···–SO3– electrostatic hydrogen-bonding network layer. Simple cation exchange in dianionic BSNDI2–salts conventionally modified the intermolecular π–π interactions in terms of dimensionality, magnitude, and electron transport properties.

In bulk materials, positional isomers not only help in understanding how slight difference in molecular structure alters the crystal packing and optical properties, but also play a key role in developing new type of materials for functional applications. A detailed study on the photophysical properties of fluorene–HBT positional isomers in solution and in the solid state providing a molecular level understanding of the factors which influence fluorescence behavior is reported. Two molecules Iaand IIawere synthesized by Suzuki coupling reaction and their photophysical properties were compared to positional isomers Iband IIb. Crystal structure analyses and density functional theory (DFT) computation studies were performed to understand structure–properties relation and the results reveal that changing substitution pattern has a marked influence on their packing modes and luminescence properties. Strong noncovalent interactions (π–π) in the solid state hamper the excited state intramolecular proton transfer (ESIPT) process which causes fluorescence quenching in the solid state (Iaand IIa= Φf, 28–40%; Iband IIb= Φf, 55–67%). Compounds show solvent–responsive and aggregation induced emission (AIE) properties. Bent structures of Iawith double and symmetric substitution of ESIPT motifs exhibit particularly unique condensed phase upon heating, confirmed as a nematic liquid crystalline phase, and this is the first report on the ESIPT and AIE active liquid crystalline materials with a banana-shaped molecule.

Synthetic challenges toward anomalous structures and electronic states often involve handling problems such as insolubility in common organic solvents and oxidative degradation under aerobic conditions. We designed benzo-annulated aza[n]helicenes, which benefit from both the suppressed elevation of highest occupied molecular orbital (HOMO) energies and high solubility due to hydrogen bonding with solvent molecules to overcome these challenges. This strategy enabled the synthesis of six new aza[n]helicenes ([n]AHs) of different lengths (n= 9–19) from acyclic precursors via one-pot intramolecular oxidative fusion reactions. The structures of all of the synthesized aza[n]helicenes were determined by X-ray diffraction (XRD) analysis, and their electrochemical potentials were measured by cyclic voltammetry. Among the synthesized aza[n]helicenes, [17]AHand [19]AHare the first heterohelicenes with a triple-layered helix. The noncovalent interaction (NCI) plots confirm the existence of an effective π–π interaction between the layers. The absorption and fluorescence spectra red-shifted as the helical lengths increased, without any distinct saturation points. The optical resolutions of N-butylated [9]AH, [11]AH, [13]AH, and [15]AHwere accomplished, and their circular dichroism (CD) and circularly polarized luminescence (CPL) were measured. Thus, the structural, (chir)optical, and electrochemical properties of the aza[n]helicenes were comprehensively analyzed.

Alkylamide-substituted [1]benzothieno[3,2-b][1]benzothiophene (BTBT) derivative of BTBT-NHCOC14H29(1), which has ferroelectric N–H···O= hydrogen-bonding network of alkylamide group and two-dimensional (2D) electric structure of BTBTπ-cores, was prepared to design the external electric field-responsive organic semiconductors. The short-chain derivative of BTBT-NHCOC3H7(1’) revealed the coexistence of a 2D electronic band structure based on the herringbone BTBTarrangement and the one-dimensional (1D) hydrogen-bonding chain. 1formed a smectic E (SmE) liquid crystal phase above 412 K and showed ferroelectric hysteresis in the electric field–polarization (P–E) curves at 403–433 K. The remanent polarization (Pr) and coercive electric field (Ec) of 1at 408 K, 0.1 Hz were 24.0 μC cm–2and 5.54 V μm–1, respectively. By thermal annealing of thin-film 1at 443 K, the molecular assembly structure of 1changed from a monolayer to a bilayer structure with high crystallinity, resulting in conducting layers of BTBTparallel to the substrate surface. The organic field-effect transistor (OFET) device with thermally annealed thin-film 1showed p-type semiconducting behavior with the hole mobility of 1.0 × 10–3cm2V–1s–1. Furthermore, device 1showed switching behavior of semiconducting properties by electric field poling and thermal annealing cycle. The electric field response of ferroelectrics modulated the molecular orientation and conduction properties of organic semiconductors, resulting in external electric field control of carrier transport properties.

Spontaneous organizations of designed elements with explicit shape and symmetry are essential for developing useful structures and materials. We report the topologically directed assemblies of four categories (a total of 24) of sphere–rod conjugates, composed of a sphere-like fullerene (C60) derivative and a rod-like oligofluorene(s) (OF), both of which are promising organic semiconductor materials. Although the packing of either spheres or rods has been well-studied, conjugates having both shapes substantially enrich resultant assembled structures. Mandated by their shapes and topologies, directed assemblies of these conjugates result not only in diverse unconventional semiconducting supramolecular lattices with controlled domain sizes but also in tunable charge transport properties of the resulting structures. These results demonstrate the importance of persistent molecular topology on hierarchically assembled structures and their final properties.

Boraphenalenes, compounds in which one carbon atom in the phenalenyl skeleton is replaced with a boron atom, have attracted attention for their solid-state and electronic structures; however, the construction of boraphenalene skeletons remains challenging because of the lack of suitable methods. Through this study, we showed that the tandem borylative cyclization of C3-symmetric dehydrobenzo[12]annulenes produces a new class of fully fused boron-atom-embedded polycyclic hydrocarbons possessing a 9b-boraphenalene skeleton. The obtained compounds exhibited high electron-accepting characteristics, and their two-step redox process was reversible in the reductive region, involving interconversion of 9b-boraphenalene between Hückel aromaticity and antiaromaticity. Notably, the benzo[b]fluorene-fused derivative exhibited a stepwise single-crystal-to-single-crystal (SCSC) phase transition triggered by thermal annealing. Intermolecular electron coupling calculation of the crystal structures suggested a significant improvement of charge transporting ability associated with the SCSC phase transition. Moreover, adequate photoconductivity was observed for the single crystals before and after the SCSC phase transition through flash photolysis-time-resolved microwave conductivity.

A two-dimensional conjugated polymer is synthesized that demonstrates low electron effective masses and high mobility. These properties show that this material could act as a viable alternative to silicon-based semiconductors.