Stacking Distances Research Articles

Color-tunable single-fluorophore supramolecular system with assembly-encoded emission

Regulating the fluorescent properties of organic small molecules in a controlled and dynamic manner has been a fundamental research goal. Although several strategies have been exploited, realizing multi-color molecular emission from a single fluorophore remains challenging. Herein, we demonstrate an emissive system by combining pyrene fluorophore and acylhydrazone units, which can generate multi-color switchable fluorescent emissions at different assembled states. Two kinds of supramolecular tools, amphiphilic self-assembly and γ-cyclodextrin mediated host-guest recognition, are used to manipulate the intermolecular aromatic stacking distances, resulting in the tunable fluorescent emission ranging from blue to yellow, including a pure white-light emission. Moreover, an external chemical signal, amylase, is introduced to control the assembly states of the system on a time scale, generating a distinct dynamic emission system. The dynamic properties of this multi-color fluorescent system can be also enabled in a hydrogel network, exhibiting a promising potential for intelligent fluorescent materials.

Probing the structural and electronic response of Magnus green salt compounds [Pt(NH2R)4][PtCl4] (R = H, CH3) to pressure.

Despite possessing the desirable crystal packing and short PtPt stacking distances required for a large piezoresistive response, the conductivity-pressure response of the Magnus green salt [Pt(NH3)4][PtCl4] is extremely sluggish. Through a combination of high-pressure X-ray diffraction and hybrid-DFT solid state calculations this study demonstrates that the poor conductivity-pressure response is due to a low volumetric compression anisotropy, a relatively large ambient pressure band gap and a lack of dispersion in the conduction band. Ligand modification (from NH3 to NH2CH3) does not enhance the piezoresistive response, causing even lower anisotropy of the volumetric compression and an unexpected phase transition at above 2 GPa. This study demonstrates that consideration of frontier band dispersion is a key design criterion, alongside crystal packing and PtPt stacking distances, for piezoresistive materials.

Sodium(I)-doped graphitic carbon nitride with appropriate interlayer distance as a highly selective sorbent for strontium(II) prior to its determination by ICP-OES.

Multilayered and porous sodium-doped graphitic carbon nitride (GCN-Na) was prepared and employed to the solid-phase extraction of Sr(II). The sorbent exhibits high adsorption capacity and excellent selectivity for Sr(II). This is due to its small interplanar stacking distance caused by doping with Na(I) which matches the size of Sr(II) better than blank GCN. An original solid-phase extraction method based on GCN-Na coupled with ICP-OES was established for Sr(II), the calibration plots are linear ranging from 0.05-10mg·kg-1 with the correlation coefficients (R2) above 0.999, the limits of detection are in the range of 0.57-1.52μg·kg-1 and the preconcentration factor of 80 is achieved using 48mL sample. It was successfully applied in the extraction and detection of trace Sr(II) in tap water, rice and sea fish. Graphical abstractA multilayer porous sodium(I) doped graphitic carbon nitride nanosheet (GCN-Na) was synthesized and exhibited excellent adsorption capability and selectivity for Sr(II).

Ultrastructural modeling of small angle scattering from photosynthetic membranes

The last decade has seen a range of studies using non-invasive neutron and X-ray techniques to probe the ultrastructure of a variety of photosynthetic membrane systems. A common denominator in this work is the lack of an explicitly formulated underlying structural model, ultimately leading to ambiguity in the data interpretation. Here we formulate and implement a full mathematical model of the scattering from a stacked double bilayer membrane system taking instrumental resolution and polydispersity into account. We validate our model by direct simulation of scattering patterns from 3D structural models. Most importantly, we demonstrate that the full scattering curves from three structurally typical cyanobacterial thylakoid membrane systems measured in vivo can all be described within this framework. The model provides realistic estimates of key structural parameters in the thylakoid membrane, in particular the overall stacking distance and how this is divided between membranes, lumen and cytoplasmic liquid. Finally, from fitted scattering length densities it becomes clear that the protein content in the inner lumen has to be lower than in the outer cytoplasmic liquid and we extract the first quantitative measure of the luminal protein content in a living cyanobacteria.

Unsymmetric Side Chains of Indacenodithiophene Copolymers Lead to Improved Packing and Device Performance

Two conjugated polymers (PuIDTBD and PuIDTQ) with unsymmetric side chains have been prepared for polymer solar cells using two other polymers (PIDTBD and PIDTQ) with symmetric side chains as control compounds. The combination of methyl and 4-hexylphenyl side chains on the same bridged carbon can ensure good solubility, decrease π-π stacking distances, and bring proper miscibility with PC71BM simultaneously. Therefore, the corresponding polymer solar cells (PSCs) based on donor polymers with unsymmetric side chains exhibited enhanced short-circuit current density (JSC) and power conversion efficiency (PCE) compared with those of control polymers. The PIDTBD and PIDTQ based devices possessed low PCE of 2.13% and 1.48%, while PCEs of devices based on PuIDTBD and PuIDTQ were improved to 3.93% and 4.12%, respectively. The results demonstrate that unsymmetric side chain engineering of conjugated polymers is an effective approach to achieve high performance PSCs.

π-π Stacking Distance and Phase Separation Controlled Efficiency in Stable All-Polymer Solar Cells.

The morphology of the active layer plays a crucial role in determining device performance and stability for organic solar cells. All-polymer solar cells (All-PSCs), showing robust and stable morphologies, have been proven to give better thermal stability than their fullerene counterparts. However, outstanding thermal stability is not always the case for polymer blends, and the limiting factors responsible for the poor thermal stability in some All-PSCs, and how to obtain higher efficiency without losing stability, still remain unclear. By studying the morphology of poly [2,3-bis (3-octyloxyphenyl) quinoxaline-5,8-diyl-alt-thiophene-2,5-diyl](TQ1)/poly[4,8-bis[5-(2-ethylhexyl)-2-thienyl]benzo[1,2-b:4,5-b′]dithiophene-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2-carboxylate-2-6-diyl]] (PCE10)/PNDI-T10 blend systems, we found that the rearranged molecular packing structure and phase separation were mainly responsible for the poor thermal stability in devices containing PCE10. The TQ1/PNDI-T10 devices exhibited an improved PCE with a decreased π–π stacking distance after thermal annealing; PCE10/PNDI-T10 devices showed a better pristine PCE, however, thermal annealing induced the increased π–π stacking distance and thus inferior hole conductivity, leading to a decreased PCE. Thus, a maximum PCE could be achieved in a TQ1/PCE10/PNDI-T10 (1/1/1) ternary system after thermal annealing resulting from their favorable molecular interaction and the trade-off of molecular packing structure variations between TQ1 and PCE10. This indicates that a route to efficient and thermal stable All-PSCs can be achieved in a ternary blend by using material with excellent pristine efficiency, combined with another material showing improved efficiency under thermal annealing.

Impact of the Siloxane-Terminated Side Chain on Photovoltaic Performances of the Dithienylbenzodithiophene-Difluorobenzotriazole-Based Wide Band Gap Polymer Donor in Non-Fullerene Polymer Solar Cells.

To thoroughly disclose the role of the siloxane-terminated side chain with different substituent positions, three difluorobenzotriazole-dithienylbenzodithiophene (FTAZ-BDTT)-based polymers PBZ-1Si, PBZ-2Si, and PBZ-3Si with the siloxane-terminated side chain on the FTAZ unit (PBZ-1Si), on the BDTT unit (PBZ-2Si), and both on BDTT and FTAZ units (PBZ-3Si), respectively, were synthesized. The different side chain substitutions have slight influences on absorption behavior, thermal stability, and frontier molecular orbitals but have shown a great effect on the aggregation of the polymers. Grazing-incidence wide-angle X-ray scattering measurements reveal that, relative to PBZ-1Si with branched alkyl on the BDTT unit, polymers PBZ-2Si and PBZ-3Si, bearing the siloxane-terminated side chains on the BDTT unit, exhibit smaller π-π stacking distances and larger crystal coherence lengths, suggesting that adopting the siloxane-terminated side chain on the BDTT unit can promote the interchain π-π interaction and the ordering of molecular packing. With IT-M as the non-fullerene acceptor, among the three polymers, the PBZ-2Si-based active layer possesses the highest ordered crystals for both polymers and IT-M as well as the purest domain, which affords efficient exciton dissociation, the most balanced hole-electron transport, and reduced recombination, leading to the highest short-circuit current density (Jsc) and fill factor (FF) and then the highest power conversion efficiency (PCE) of 11.14%. In contrast, PBZ-1Si- and PBZ-3Si-based devices show lower PCEs of 8.98 and 9.92%, respectively. Moreover, PBZ-2Si:IT-M also exhibits good thickness tolerance, and its thick active layer of 240 nm shows the most limited decrease of efficiency after 77 days of storage, supplying good potential for mass fabrication. Our work suggests that the fine pairing of a siloxane-terminated side chain and an alkyl side chain is beneficial for the optimizing of a conjugated polymer donor toward high-performance non-fullerene polymer solar cells.

Redetermination of the crystal structure of tetrammineplatinum(II) dichloride – A microporous hydrogen-bonded 3D network exhibiting a temperature-dependent order-disorder phase transition

The title compound [Pt(NH3)4]Cl2 (1), prepared by reaction of (NH4)2[PtCl4] with an excess of NH3 in aqueous solution, was crystallized from water and its structure redetermined by single-crystal X-ray diffraction at four different temperatures in the range from 273 K down to 100 K. 1 is composed of square-planar [Pt(NH3)4]2+ complex cations and Cl− anions and crystallizes in the tetragonal crystal system. Remarkably, the solid state structure is porous (approx. 18% of the crystal volume is void space) and features one-dimensional open channels of a diameter of ∼3–4 Å. Unexpectedly, these channels are free of solvent molecules, although the crystals were obtained from aqueous solutions. NH⋯Cl hydrogen bonding interactions between the square-planar [Pt(NH3)4]2+ dications and the Cl− counter ions result in a three-dimensional hydrogen bonding network that stabilizes the porous solid state structure. The hydrogen atoms of the ammonia ligands and their corresponding NH⋯Cl hydrogen bonds are localized at low temperature (space group I4/mmm) but disorder dynamically above 173 K (space group P4/mmm). The order-disorder transition is accompanied by significant changes in the Pt–Pt stacking distances and a fourfold reduction of the unit cell volume.

Enhancing optical absorption and charge transfer: Synthesis of S-doped h-BN with tunable band structures for metal-free visible-light-driven photocatalysis

Two-dimensional materials, especially metal-free two-dimensional materials such as graphene, carbon nitride and boron nitride have attracted significant attention for photocatalysis technology due to their unique charge mobility. Herein, S-doped h-BN with tunable band structure and layer stacking distance has been developed via a facile heat treatment strategy. Compared to the pristine h-BN, the optimized S-doped h-BN exhibited enhanced optical absorption, charge transfer, surface reactivity and hydrophilicity, which greatly improved its ability for photocatalytic degradation of 2,4-DCP. It is clearly demonstrated, by means of various experiments and characterizations, that the bandgap and layer spacing of h-BN can be adjusted by controlling the S doping amount. DFT calculations exposed that the p-orbitals and d-orbitals from sulfur are involved in the formation of the new valence and conduction band edges, which gradually reduced the CB potential, narrowed the bandgap and enhanced the optical absorption property of h-BN. And the shortened layer stacking distance and abundant S doping sites may be the main reason for the promotion of charge mobility and surface reactivity. Through this strategy, h-BN was vested with the ability of visible light response, which provides insights for the modification of other semiconductor materials with wide bandgap, and the study on the compression compaction phenomenon of interlayer stacking distance can open up a new feasible route to enhance charge mobility of other two-dimensional semiconductor materials.

The Effect of Pressure on Halogen Bonding in 4-Iodobenzonitrile

The crystal structure of 4-iodobenzonitrile, which is monoclinic (space group I2/a) under ambient conditions, contains chains of molecules linked through C≡N···I halogen-bonds. The chains interact through CH···I, CH···N and π-stacking contacts. The crystal structure remains in the same phase up to 5.0 GPa, the b axis compressing by 3.3%, and the a and c axes by 12.3 and 10.9 %. Since the chains are exactly aligned with the crystallographic b axis these data characterise the compressibility of the I···N interaction relative to the inter-chain interactions, and indicate that the halogen bond is the most robust intermolecular interaction in the structure, shortening from 3.168(4) at ambient pressure to 2.840(1) Å at 5.0 GPa. The π∙∙∙π contacts are most sensitive to pressure, and in one case the perpendicular stacking distance shortens from 3.6420(8) to 3.139(4) Å. Packing energy calculations (PIXEL) indicate that the π∙∙∙π interactions have been distorted into a destabilising region of their potentials at 5.0 GPa. The structure undergoes a transition to a triclinic () phase at 5.5 GPa. Over the course of the transition, the initially colourless and transparent crystal darkens on account of formation of microscopic cracks. The resistance drops by 10% and the optical transmittance drops by almost two orders of magnitude. The I···N bond increases in length to 2.928(10) Å and become less linear [<C−I∙∙∙N = 166.2(5)°]; the energy stabilises by 2.5 kJ mol−1 and the mixed C-I/I..N stretching frequency observed by Raman spectroscopy increases from 249 to 252 cm−1. The driving force of the transition is shown to be relief of strain built-up in the π∙∙∙π interactions rather than minimisation of the molar volume. The triclinic phase persists up to 8.1 GPa.

Organic nanoparticles with efficient and adjustable exciplex emission for biological imaging

The mixing of donor and acceptor molecules in fluorescent nanoparticles offers an effective route to adjusting the emission properties of the nanoparticles. In this work, the electron donor 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) and the electron acceptor 2,4-bis[4-(diphenylphosphinyl)phenyl]-6-[4-(hexyloxy)phenyl]-1,3,5-triazine (BPOTZ-OR) were coprecipitated to form fluorescent nanoparticles. Efficient exciplex emission occurred in the nanoparticles owing to the good electron affinity and appropriate stacking distance between TAPC and BPOTZ-OR. The exciplex emission and monomer emission were easily tuned by simply changing the BPOTZ-OR/TAPC molar ratio. An appropriate combination produced white-light emission. The large red-shift of the emission from the exciplex, good stability under physiological conditions, and low toxicity suggest potential for this kind of nanoparticle to be an effective fluorescent probe for cell imaging.

Fine‐Tuning Aromatic Stacking and Single‐Crystal Photoluminescence Through Coordination Chemistry

Organic aromatics usually show a decrease in fluorescence efficiency in the solid state on account of well‐known aggregation induced quenching. We have found that single crystals of coordination polymers consisting of γ‐aminobutyric acid functionalized naphthalenediimide ligand (H2GABA‐NDI) can give rise to highly emissive, broad, and red‐shifted photoluminescence (PL) in the solid state. To better understand the origin of the bandwidth broadening with the π–π stacking distances, we performed time‐resolved PL studies in a series of polymers with a variety of metal centers. We conclude that the broad steady‐state PL signals is originated from a superposition of two emissive states with differing energy and lifetimes, with the lower energy one produced by the interchromophoric interactions mediated by π–π stacking of neighboring NDI units. Our work demonstrates that coordination chemistry is an effective tool to modulate interchromophoric couplings and that simple PL analysis can be used as a measure of the degree of π‐stacking.

Mixed-Valent Cyanoplatinates Featuring Neptunyl-Neptunyl Cation-Cation Interactions.

The tetracyanoplatinate ligand was employed in synthesizing the first neptunyl cyanoplatinate complexes. Results indicate in situ oxidation of Pt(II) by Np(V/VI) to form mixed-valent Pt-Pt stacked columnar chains linked by cation-cation interaction induced chains of Np(V) polyhedra into a two-dimensional sheet structure. The Pt-Pt stacking distances of 3.04-3.05 Å are the longest reported columnar platinophilic interactions among mixed-valent tetracyanoplatinate structures. These complexes further illustrate the marked chemical differences and structural diversity of solid-state Np(V) coordination complexes with regard to Np(VI) and U(VI).

Enhanced thermoelectric properties of two-dimensional conjugated polymers

Organic thermoelectric materials have drawn great attention in the past years. In this study, we report the thermoelectric properties of ferric salt bis(trifluoromethane)sulfonimide (TFSI−) doped two-dimensional (2D) conjugated polymer, poly[[4,8-bis[(5-ethylhexyl)thienyl]benzo[1,2-b;3,3-b]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7-DT). It is found that the electrical conductivities of TFSI− doped 2D PTB7-DT are nearly 100 times larger than those of TFSI− doped one-dimensional (1D) corresponding conjugate polymer, poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7) at the same doping levels. Moreover, TFSI− doped 2D PTB7-DT possess over 20 times larger power factor (79.8 μW/mK2) than that of TFSI− doped 1D PTB7. The enhancement of electrical conductivities of TFSI− doped 2D PTB7-DT is attributed to enhanced charge carrier densities and polaron densities. The studies of grazing incidence wide angle X-ray scattering further indicate that the π-π stacking distances of TFSI− doped 2D PTB7-DT along the in-plane direction are largely reduced compared to that of TFSI− doped 1D PTB7, which would facilitate the inter-chain and the intra-chain charge carrier transport, resulting in enhanced electrical conductivities. All these results demonstrate that 2D conjugated polymers are promising candidate materials for approaching high performance organic thermoelectric electronics.

Micro‐Layer and Lattice Structure Effects on Impedance of Titanium Oxide Phthalocyanine

In this study, the authors employ synchrotron techniques to characterize multi‐scale microstructure in elucidating how the modified crystal lattices at angstrom level and molecular stacking at micrometer scale of titanium oxide phthalocyanine (TiOPc) thin film tuning the impedance. The a and c lattice lengths of the TiOPc reveal a positive correlation with the impedance because of the π‐π stacking distances of TiOPc molecules arrangements. Our results suggest a promising dip coating method to tailor the charge storage capability of TiOPc through controlling the crystal lattice sizes of TiOPc.

Polythiophenes with carboxylate side chains and vinylene linkers in main chain for polymer solar cells

Two polythiophenes with carboxylate side chains and vinylene linkers in conjugated backbones, i.e., poly[5,5′-(E)-bis(2-hexyldecyl)-2,2′-(ethene-1,2-diyl)bis(thiophene-3-carboxylate)-alt-5,5′- 2,2′-bithiophene] (PBT) and poly[5,5′-(E)-bis(2-hexyldecyl)-2,2′-(ethene-1,2-diyl) bis(thiophene-3-carboxylate)-alt-5,5′-thieno[3,2-b]thiophene] (PTT), were synthesized and characterized. Compared to poly(3-hexylthiophene) (P3HT), both polymers displayed deeper HOMO energy levels caused by the introduction of the electron-withdrawing carboxylate group and lower band gaps and shorter π-π stacking distances (ca. 3.5 Å) due to the incorporation of vinylene linkers in the conjugated backbones. Polymer PBT possesses greater self-organization ability and thereby more ordered intermolecular packing in solid state. Consequently, organic field-effect transistors (OFETs) based on PBT showed a hole mobility of 0.24 cm2 V−1s−1, much higher than that (0.073 cm2 V−1s−1) of PTT. Polymer solar cells (PSCs) with the two polymers as donor materials and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as acceptor material were fabricated, and both PBT- and PTT-based PSCs showed open circuit voltage (Voc) above 0.8 V. Owing to the better hole transport property and more ordered nano-fibrillar film morphology, PBT-based PSCs exhibited a superior photovoltaic performance with power conversion efficiency (PCE) of 6.25%, higher than that of PTT-based PSCs (PCE = 5.53%). This study indicates that simultaneously introducing electron-withdrawing carboxylate in side chains and vinylene linkers in conjugated backbones could efficiently tune the energy levels and enhance the π-π interactions between conjugated backbones.

Nonmetal element doped g-C3N4with enhanced H2evolution under visible light irradiation

Abstract

High-performance FDTE-based polymer semiconductors with F⋯H intramolecular noncovalent interactions: Synthesis, characterization, and their field-effect properties

Herein, we report two novel donor-acceptor copolymers, PFDTE1 and PFDTE2, based on (E)-1,2-bis(3-fluorothiophen-2-yl)ethene (FDTE) moiety. X-ray diffraction crystallography indicated that F⋯H hydrogen bonds exist in single FDTE unit. Theoretical simulation results revealed that the FDTE unit owns increased torsional potential due to the presence of fluorine-induced intramolecular noncovalent interactions. The two copolymers exhibited ambipolar carrier transport characteristics, with hole/electron mobilities of 4.24/0.30 cm2 V−1 s−1 for PFDTE1 and 5.42/0.36 cm2 V−1 s−1 for PFDTE2. The complementary-like inverters based on PFDTE2 were also successfully fabricated and showed high gain values of 104 and 115, respectively, providing potential in ambipolar complementary-like inverters. AFM and 2D-GIXRD analyses revealed that the two copolymers formed lamellar, edge-on molecular packing, and crystalline thin films with small π–π stacking distances down to 3.55 Å.

Electronic structure, lattice dynamics, and optical properties of a novel van der Waals semiconductor heterostructure: InGaSe2

There is a growing interest in the property dependence of transition metal dichalcogenides as a function of the number of layers and formation of heterostructures. Depending on the stacking, doping, edge effects, and interlayer distance, the properties can be modified, which opens the door to novel applications that require a detailed understanding of the atomic mechanisms responsible for those changes. In this work, we analyze the electronic properties and lattice dynamics of a heterostructure constructed by simultaneously stacking InSe layers and GaSe layers bounded by van der Waals forces. We have assumed the same space group of GaSe, $P\overline{6}m2$ as it becomes the lower energy configuration for other considered stackings. The structural, vibrational, and optical properties of this layered compound have been calculated using density functional theory. The structure is shown to be energetically, thermally, and elastically stable, which indicates its possible chemical synthesis. A correlation of the theoretical physical properties with respect to its parent compounds is extensively discussed. One of the most interesting properties is the low thermal conductivity, which indicates its potential use in thermolectric applications. Additionally, we discuss the possibility of using electronic gap engineering methods, which can help us to tune the optical emission in a variable range close to that used in the field of biological systems (NIR). Finally, the importance of considering properly van der Waals dispersion in layered materials has been emphasized as included in the exchange correlation functional. As for the presence of atoms with important spin-orbit coupling, relativistic corrections have been included.

Studies on complex π-π and T-stacking features of imidazole and phenyl/p-halophenyl units in series of 5-amino-1-(phenyl/p-halophenyl)imidazole-4-carboxamides and their carbonitrile derivatives: Role of halogens in tuning of conformation

5-amino-1-(phenyl/p-halophenyl)imidazole-4-carboxamides (N-phenyl AICA) (2a-e) and 5-amino-1-(phenyl/p-halophenyl)imidazole-4-carbonitriles (N-phenyl AICN) (3a-e) had been synthesized. X-ray crystallographic studies of 2a-e and 3a-e had been performed to identify any distinct change in stacking patterns in their crystal lattice. Single crystal X-ray diffraction studies of 2a-e revealed π-π stack formations with both imidazole and phenyl/p-halophenyl units in anti and syn parallel-displaced (PD)-type dispositions. No π-π stacking of imidazole occurred when the halogen substituent is bromo or iodo; π-π stacking in these cases occurred involving phenyl rings only. The presence of an additional T-stacking had been observed in crystal lattices of 3a-e. Vertical π-π stacking distances in anti-parallel PD-type arrangements as well as T-stacking distances had shown stacking distances short enough to impart stabilization whereas syn-parallel stacking arrangements had got much larger π-π stacking distances to belie any syn-parallel stacking stabilization. DFT studies had been pursued for quantifying the π-π stacking and T-stacking stabilization. The plotted curves for anti-parallel and T-stacked moieties had similarities to the ‘Morse potential energy curve for diatomic molecule’. The minima of the curves corresponded to the most stable stacking distances and related energy values indicated stacking stabilization. Similar DFT studies on syn-parallel systems of 2b corresponded to no π-π stacking stabilization at all. Halogen-halogen interactions had also been observed to stabilize the compounds 2d, 2e and 3d. Nano-structural behaviour of the series of compounds 2a-e and 3a-e were thoroughly investigated.