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In dynamic data structures, one is interested in efficiently facilitating queries to a data set, while being able to efficiently perform updates as the data set undergoes changes. Often, relaxing the efficiency measure to the amortised setting allows for simpler algorithms. A well-known example of a data structure with amortised guarantees is the splay tree by Sleator and Tarjan [Daniel D. Sleator and Robert E. Tarjan, 1985]. Similarly, in data structures for dynamic graphs, one is interested in efficiently maintaining some information about the graph, or facilitating queries, as the graph undergoes changes in the form of insertion and deletion of edges. Examples of such information include connectivity, planarity, and approximate sparsity of the graph: is the graph presently connected? Is it planar? Has its arboricity grossly exceeded some specified number α̃? The related queries could be: is a connected to b? Are the edges uv and uw consecutive in the ordering around u in its current planar embedding? Or, report the O(α) out-edges of vertex x. In this talk, we will see Brodal and Fagerberg’s amortised algorithm for orienting sparse graphs (i.e. of arboricity ≤ α), so that each vertex has O(α) out-edges [Gerth Stølting Brodal and Rolf Fagerberg, 1999]. The algorithm itself is extremely simple, and uses an elegant amortised argument in its analysis. Then, we will visit the problem of dynamic planarity testing: is the graph presently planar? Here, we will see an elegant amortised reduction to the seemingly easier problem, where planarity-violating edges may be detected and rejected [Eppstein et al., 1996]. We will see a sketch of how the current state-of-the-art algorithm for efficient planarity testing [Jacob Holm and Eva Rotenberg, 2020] uses ideas similar to those in [Gerth Stølting Brodal and Rolf Fagerberg, 1999] to analyse the behaviour of a greedy algorithm via a possibly inefficient algorithm with provably low recourse [Jacob Holm and Eva Rotenberg, 2020]. If time permits, we will touch upon a recent simple amortised data structure for maintaining information in dynamic forests [Jacob Holm et al., 2023], which builds on ideas from splay trees. The talk concludes with some open questions in the area., LIPIcs, Vol. 254, 40th International Symposium on Theoretical Aspects of Computer Science (STACS 2023), pages 2:1-2:2

The question if a given partial solution to a problem can be extended reasonably occurs in many algorithmic approaches for optimization problems. For instance, when enumerating minimal dominating sets of a graph $G=(V,E)$, one usually arrives at the problem to decide for a vertex set $U \subseteq V$, if there exists a \textit{minimal} dominating set $S$ with $U\subseteq S$. We propose a general, partial-order based formulation of such extension problems and study a number of specific problems which can be expressed in this framework. Possibly contradicting intuition, these problems tend to be NP-hard, even for problems where the underlying optimisation problem can be solved in polynomial time. This raises the question of how fixing a partial solution causes this increase in difficulty. In this regard, we study the parameterised complexity of extension problems with respect to parameters related to the partial solution, as well as the optimality of simple exact algorithms under the Exponential-Time Hypothesis. All complexity considerations are also carried out in very restricted scenarios, be it degree restrictions or topological restrictions (planarity) for graph problems or the size of the given partition for the considered extension variant of Bin Packing.

Highly crystalline covalent organic frameworks (COFs) or conjugated polymers (CPs) are very important and highly desirable because these materials would display better performance in diverse devices and provide more structure-property related information. However, how to achieve highly crystalline or single-crystal COFs and CPs is very challenging. Recently, many research studies have demonstrated the possibility of enhancing the crystallinity of COFs and CPs. Thus, it is timely to offer an overview of the important progress in improving the crystallinity of COFs and CPs from the viewpoint of design strategies. These strategies include polycondensation reaction optimization, improving the planarity, fluorine substitution, side chain engineering, and so on. Furthermore, the challenges and perspectives are also discussed to promote the realization of highly crystalline or single-crystal COFs and CPs.

Polycyclic aromatic hydrocarbons (PAHs) are widely used in organic electronic devices. The electronic, magnetic, and optical properties of PAHs can be tuned by structural modifications to the aromatic backbone to introduce an inherent distortion from planarity, such as bending or twisting. However, it remains difficult to isolate and control the effects of such distortions. Here, we sought to understand how backbone twisting and bending affect the electronic properties of acenes, as models for larger PAHs. We found that, even when highly distorted from planarity (30° per ring), acenes maintain their aromatic character and π orbital delocalization with minor mixing of the σ and π orbitals. In addition, the energy gap between the HOMO and LUMO decreases with increasing twist, while the gap is hardly affected by bending, since the energy of both orbitals increase to a similar extent. For bent acenes in the triplet state, the spin becomes more localized with increasing bend, whereas twisting produces an evenly distributed spin delocalization. These findings can guide the synthesis of PAHs with tailored properties., A computational study performed on nonplanar acenes demonstrates the different effects of bending and twisting on the effect on their electronic properties.

Structural design of organic π-conjugated small molecules allows the energy band structure and electronic properties of the molecules to be tuned as needed, which provides a feasible strategy for enhancing the performance of optoelectronic devices. The introduction of bridging structures is a common structural modification method to adjust the rigidity and coplanarity of the molecular backbone, thus affecting the molecular packing. However, patterning of organic single-crystalline microstructures based on conjugated ladder molecules with different bridging structures still remains challenging for large-area integration of optoelectronic devices. In this paper, a controlled dewetting process is applied to obtain organic single-crystalline arrays with precise positioning and a regular morphology based on two isomers with silicon-oxygen bridging and their two carbon-oxygen-bridged analogues. Molecules with different bridging structures show disparate packing models due to the difference of dihedral angles and ring tensions. A microwire-array ultraviolet photodetector based on the oxygen-silicon-bridging ladder molecule exhibits a high light on/off ratio of 24 and a responsivity of 0.63 mA W-1 owing to the effective π-π stacking governed by the molecular planarity. This work not only provides a universal method for the integration of organic optoelectronic devices but also explains the effect of bridging structure engineering on molecular assembly and optoelectronic performance.

Fluorophores with emission in the second near-infrared window (NIR-II) have displayed salient advantages for biomedical applications. However, the common strategy of reducing the energy bandgap of fluorophores so as to achieve red-shifted wavelengths always leads to compromised fluorescent brightness. Herein, we propose a molecular design concept of "ring-fusion" to modify the acceptor of AIEgen that can extend the luminous wavelength from NIR-I to NIR-II. The fused-acceptor-containing fluorophore yielded, TTQP, has an enhanced absorption coefficient with a higher brightness in nanoparticle formation compared to its NIR-I emissive counterpart (TTQ-DP) with a non-fused acceptor. Theoretical calculation further confirms that the ring fusion can efficiently promote the rigidity and planarity of the electron-deficient core, leading to a lower reorganization energy and nonradiative decay. The TTQP NPs yielded thus allow sensitive NIR-II fluorescence imaging of vasculature and intestinal inflammation in mice models. Therefore, we anticipate that our work will provide a promising molecular-engineering strategy to enrich the library and broaden the application scope of NIR-II fluorophores.

Summary The structure and reactivity of silicon(IV), the second most abundant element in our Earth's crust, is determined by its invariant tetrahedral coordination geometry. Silicon(IV) with a square-planar configuration (ptSiIV) represents a transition state. Quantum theory supported the feasibility of stabilizing ptSiIV by structural constraint, but its isolation has not been achieved yet. Here, we present the synthesis and full characterization of the first square-planar coordinated silicon(IV). The planarity provokes an extremely low-lying unoccupied molecular orbital that induces unusual silicon redox chemistry and CH-agostic interactions. The small separation of the frontier molecular orbitals enables visible-light ligand-element charge transfer and bond-activation reactivity. Previously, such characteristics have been reserved for d-block metals or low-valent p-block elements. Planarization transfers them, for the first time, to a p-block element in the normal valence state., Graphical abstract, Highlights • The first square-planar silicon(IV) is isolated • A low-lying LUMO provokes CH-agostic interaction and visible-light absorption • Transition metals are mimicked without leaving the natural oxidation state, The bigger picture Tetrahedral silicon(IV) compounds are the building blocks of our Earth’s crust. Here, we describe the first species of silicon(IV) with a square-planar configuration. The structural deformation has substantial consequences for the compounds’ physicochemical properties and imparts features usually associated with transition metals. Upon planarization, the frontier molecular orbital gap shrinks by more than 50% and enables ligand-element charge transfer, CH-bond agostic interactions, and spontaneous reactivity with inert bonds. Small frontier molecular orbital gaps are critical for bond-activation reactivity, catalysis, and photochemistry with transition metals. Traditional approaches to mimic these characteristics with the more abundant p-block elements rely on unusual valence or oxidation states. With the realization of square-planar silicon(IV), these peculiarities start reaching p-block elements in their natural oxidation states., Our Earth’s crust is covered with compounds of silicon(IV). In each, tetracoordinated silicon(IV) arranges its four substituents in a tetrahedral fashion, while other environments are unknown. This work describes the isolation and properties of a molecular complex with square-planar silicon(IV). The flattened structural motif provokes a range of features that primes the second most abundant element for new applications in catalysis and materials science.

In comparison with the common-used electron donor (D)-electron acceptor (A) type symmetric polymers with regular structures, their asymmetric counterparts have received much less attention and seldom been applied in polymer solar cells. Since the precise modulation of π bridge can significantly influence the photoelectric properties of D-A type polymers, π bridges of tailorable thiophenes are introduced into benzodithiophene (BDT)-benzodithiophene-4,8-dione (BDD) copolymers in both symmetric and asymmetric patterns. Together with the halogen substituent of fluorine or chlorine on BDT, four polymer donors are designed and synthesized. As expected, PTB2T-F and PTB2T-Cl with the asymmetric π bridges of thiophene and hexyl-bithiophene exhibit better planarity, stronger intermolecular interaction and higher hole mobility than P2TB2T-F and P2TB2T-Cl with the symmetric π bridges of hexyl-bithiophene. The more suitable phase separation and optimized nanomorphology is determined by the reasonable miscibility between asymmetric polymer and acceptor, which is evaluated by Flory-Huggins interaction, contributing to the extremely higher performance than that of symmetric counterpart. Moreover, paired with IT-4F as the acceptor, PTB2T-F affords better device performances than the reference BDT-BDD polymer PM6 with the symmetry π bridge of thiophene. These results demonstrate that the precise modulation of asymmetric π bridges is a promising strategy to construct high-efficiency D-A type polymer donors.

The correlation of the rotation about the Cα-C' bond and the pyramidalization of the sp2-hybridized carbon atom C' and its three bonding partners to a flattened tetrahedron in the substructure Cβ-CαH-C'(═O)-OMe of substituted methyl acetates revealed that the two processes are not independent of each other but parts of a common molecular motion, as outlined in the preceding back-to-back paper. In the present study, we generalized the substructure to Xβ-CαH-C'(═Y)-Z with X, Y, and Z = O, N, C, and S, extending the analysis to several hundred thousand structures of the type carboxylates, carboxamides, ketones, imines, olefins, peptides, lactates, carbothioates, and phenyl derivatives, retrieved from the Cambridge Structural Database. ψ/θ Scatter plots of the individual structure points and their averaging in ψ/θav curves result in wavelike patterns with three maxima and minima and inversion symmetry at ψ = 0° and ±180 for a 360° rotation of Cβ about the Cα-C' bond. The pyramidalization of the sp2-hybridized group CαCiCoCo', which is part of the aromatic system, even disturbs the planarity of phenyl rings. Density functional theory calculations confirm the results of the CSD search.

The correlation of the rotation about the bond C'-Cα and the pyramidalization of the sp2 hybridized carbon atom C' and its three bonding partners to a flattened tetrahedron was investigated for the substructure Cβ-CαH-C'(═O)-OMe. A search in the Cambridge Structural Database (CSD) gave 15,295 structures with a substituted methyl acetate group at the end of the molecules. The scatter plot of the rotation angle ψ = O═C'-Cα-Cβ versus the pyramidalization angle θ = O(MeO)C'Cα and the ψ/θav curve show an unusual undulating pattern with three maxima and minima for a 360° rotation about the bond C'-Cα. There is no net chiral induction from the (Mψ)/(Pψ) conformations of the bond C'-Cα to the (Rθ)/(Sθ) configurations of the flattened tetrahedron because the contributions of the three maxima and minima cancel each other. The wavelike ψ/θav curve demonstrates that the rotation about the bond C'-Cα and the pyramidalization of the group C'(═O)(OMe)Cα are not independent processes. They are coupled with each other in one common molecular motion. The ψ/θav curve appears as the third harmonic of a sinusoidal fundamental frequency. DFT calculations of the propanoate anion, methyl propanoate, and methyl 2-methylpropanoate confirm the results of the CSD search.

The objective of this work was to develop a synthesis, characterization, and conformational study of 4-hydroxychalcone. The chalcone was obtained using Claisen-Schmidt reaction. The product was characterized by IR and NMR spectroscopy. The latter technique was extremely important to verify the presence of the vinyl double bond formed in the reaction and to determine its trans configuration. The antioxidant activity of 4-hydroxychalcone showed a satisfactory result when compared to antioxidants already reported in the literature, with 63.4% inhibition of the DPPH radical. Also, theoretical calculations were performed to determine conformational preference. The s-cis (b) (52.0%) and the s-cis (a) (35.0%) conformers showed less energy when compared to s-trans conformers, due to the higher stabilizing effect of electron delocalization involving the p orbitals resulting from the higher planarity of s-cis conformers. However, the s-cis (a) conformer showed greater stabilization energy (510.37 kcal mol-1) in relation to the s-cis (b) conformer (505.32 kcal mol-1), this fact might be explained by the hydroxyl group interaction with the aromatic ring B, as observed by the NBO calculations. DOI: http://dx.doi.org/10.17807/orbital.v13i2.1485

Introducing two-dimensional (2D) conjugated structures to polymers is a feasible way for the design of functionalized polymers due to their good planarity, high electron/hole mobility, thermal stab...

A 1-planar graph is a graph which has a drawing on the plane such that each edge has at most one crossing. Czap and Hudak showed that every 1-planar graph with n vertices has crossing number at most $$n-2$$ . In this paper, we prove that every maximal 1-planar graph G with n vertices has crossing number at most $$n-2-(2\lambda _1+2\lambda _2+\lambda _3)/6$$ , where $$\lambda _1$$ and $$\lambda _2$$ are respectively the numbers of 2-degree and 4-degree vertices in G, and $$\lambda _3$$ is the number of odd vertices w in G such that either $$d_G(w)\le 9$$ or $$G-w$$ is 2-connected. Furthermore, we show that every 3-connected maximal 1-planar graph with n vertices and m edges has crossing number $$m-3n+6$$ .

In this work, three novel nonmetallic pentazole salts (6–8) based on furazan or 4-nitropyrazole were synthesized. Some coplanar groups were introduced into the compounds to improve the planarity of...

Upon cooling a solution of poly(2-methoxy-5- (2-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV), a phase transition occurs, leading to the formation of aggregates. We have studied the dynamics of singlet excitons in MEH-PPV solution below the critical temperature of the phase transition using steady-state photoluminescence measurements and pump−probe fs-spectroscopy at different temperatures. Spectral analysis indicates the coexistence of disordered chromophores with highly planarized chromophores. The high planarity is evidenced by a remarkably high 0−0/0−1 peak ratio in the spectra. By spectrally separating the contributions of either type of chromophore to the pump−probe signal we find that energy transfer takes place within less than 1 ps from disordered, unaggregated chain segments to highly planarized, aggregated chain segments. The short time scale of the energy transfer indicates intimate intermixing of the planarized and disordered polymeric chromophores.

Fully aromatic polyimides are amenable to efficient carbonization in thin two-dimensional (2D) films due to a complement of aromaticity and planarity of backbone repeating units. However, repeating unit rigidity traditionally imposes processing limitations, restricting many fully aromatic polyimides, e.g., pyromellitic dianhydride with 4,4'-oxidianiline (PMDA-ODA) polyimides, to a 2D form factor. Recently, research efforts in our laboratories enabled additive manufacturing of micron-scale resolution PMDA-ODA polyimide objects using vat photopolymerization (VP) and ultraviolet-assisted direct ink write (UV-DIW) following careful thermal postprocessing of the three-dimensional (3D) organogel precursors to 400 °C. Further thermal postprocessing of printed objects to 1000 °C induced pyrolysis of the PMDA-ODA objects to disordered carbon. The pyrolyzed objects retained excellent geometric resolution, and Raman spectroscopy displayed characteristic disordered (D) and graphitic (G) carbon bands. Scanning electron microscopy probed the cross-sectional homogeneity of the carbonized samples, revealing an absence of pore formation during carbonization. Likewise, impedance analysis of carbonized specimens indicated only a moderate decrease in conductivity compared to thin films that were pyrolyzed using an identical carbonization process. Facile pyrolysis of PMDA-ODA objects now enables the production of carbonaceous monoliths with complex and predictable three-dimensional geometries using commercially available starting materials.

An unexpected side product of a McMurry reaction was found to be a new [2.2]pyrenophane consisting of two pyrene units with different substitution patterns as well as different types and degrees of distortion from planarity. The new pyrenophane exhibits both monomer and intramolecular excimer fluorescence. Natural bond orbital (NBO) analysis revealed that there is an intramolecular charge-transfer interaction from the more distorted pyrene system to the less distorted one. The origin of the new pyrenophane was traced back to an impurity that was present a full five steps prior to the McMurry reaction from which it was isolated. The pathway to the pyrenophane shadowed that of the main synthetic route.

Dummy filling is widely applied to significantly improve the planarity of topographic patterns for the chemical mechanical polishing process in VLSI manufactures. The main challenge of dummy filling is balancing multiple objectives, such as fill amounts, planarity, parasitic capacitance, etc. An obvious drawback of traditional rule-based dummy filling methods is pattern densities, instead of post-chemical mechanical polishing (CMP) topographies, being included in optimization objectives. Although the quality of post-CMP topography strongly depends on pattern features of layouts, especially the density uniformity, however, experimental results show that chip surface variations are not exactly the same as density variations. In this article, a unified dummy fill insertion optimization framework is proposed, integrated with the multiple starting points-sequential quadratic programming (MSP-SQP) optimization solver, where all objectives are considered without approximation. Inside this framework, a full-chip CMP simulator is first integrated to evaluate the planarity of the chip surface. By selecting the initial points smartly with heuristic prior knowledge, the proposed method can be effectively accelerated. The effectiveness of the proposed algorithm is verified with the average 25.8% improvement of quality compared with rule-based methods.

Three spiro[fluorene-9,9′-xanthene] (SFX)-based organic molecules with different donor units were synthesized and used as dopant-free hole-transport materials (HTMs) in perovskite solar cells (PSCs). The end-capping donor units on the SFX core are two methoxydiphenylamine-substituted diphenylamine (MDDPA), two and four methoxydiphenylamine-substituted carbazole (MDCZ) for SFX-2DPA, SFX-2CZ and SFX-4CZ, respectively. The structure-function relationship is systematically investigated as the impact of the different donor units upon the optical, electrochemical and photophysical properties of SFX-based HTMs. The PSCs based on SFX-2CZ attain the higher power conversion efficiency (PCE) of 15.83% than that based on SFX-2DPA (14.25%), due to higher molecular planarity of SFX-2CZ with enhanced hole transporting ability and the downshifted HOMO level. On other hands, SFX-4CZ has the lowest efficiency (12.19%) among three HTMs mainly due to its inferior film-forming ability. The results provide not only the new molecular design of dopant-free organic HTMs based on SFX core, but also a promising strategy to develop efficient HTMs with both the molecular planarity and number of donor groups being considered.

We give a brief review of an upper limb movement model and a detailed plan of experimental study of rapid goal-directed force of upper limb movement during hammering nails. An experimental study is described. Statistical criteria for estimation of movement planarity are formulated. A conclusion about the applicability of a planar model for calculation of upper limb muscle forces is drawn, based on results of a performed trial experimental study.

In this study, the embedding of picture fuzzy graphs on the surface of spheres is introduced. The picture fuzzy genus graph with its genus value and strong (weak) picture fuzzy genus graphs are defined. Some important properties of picture fuzzy genus graphs are discussed. A relation between genus value and degree of planarity of picture fuzzy graph is established. The isomorphism properties of picture fuzzy genus graphs are studied. The Euler polyhedral equation in terms of genus value is established here. Finally, two real-life applications of picture fuzzy genus graph in traffic problem on road network and electronic circuit design on planar sheet are exhibited.

A helically twisted ribbon-shaped nanographene 3 containing four pentagons, eighteen hexagons and four heptagons was synthesized by a cascade of classical Scholl and non-classical Scholl-type cycloheptatriene formation reactions. In the pivotal step of the synthesis, ten carbon-carbon bonds and four cycloheptatriene rings were formed in one single operation in 11% yield. In this way, the fenestrindane core 1 was annelated with two m-quaterphenyl units 4 at opposite rims, generating a unique helically twisted structure 3 with D-2-symmetry. X-ray crystallography confirmed this [5.5.5.5]fenestrane-based molecular topology and revealed the aggregation of a pair of antipodal enantiomers, (M)-3 and (P)-3, in the solid state. The torsion angles, planarity of hexagons in the two tribenzo[fg,ij,rst]pentaphene substructures and the local aromaticity of the hexagons were studied based on the crystal data. The optical and electronic properties of compound 3 were investigated by UV/Vis and fluorescence spectroscopy and cyclic voltammetry. Based on the reactions of several partially cyclized intermediates and DFT calculations, a mechanistic sequence of the reaction pathways towards the formation of the nanographene 3 is proposed. In particular, factors that affect the relative ease and the role of hydride abstraction from one of the sp(3)-hybridized benzhydrylic bridgeheads, giving rise to cycloheptatrien-7-ol side products, are unfolded in this study. It is demonstrated that this side track occurs exclusively at the most highly conjugated pi-electron system formed and efficiently competes with the classical and non-classical Scholl cyclodehydrogenation reactions in the last stage of the reaction sequence.

Let $ G $ be a finite group. A bipartite graph associated to elements and cosets of subgroups of $ G $ is the simple undirected graph $ \Gamma(G) $ with the vertex set $ V(\Gamma(G)) = A\cup B $, where $ A $ is the set of all elements of a group $ G $ and $ B $ is the set of all subgroups of a group $ G $ and two vertices $ x \in A $ and $ H \in B $ are adjacent if and only if $ xH = Hx $. In this article, several graph theoretical properties are investigated. Also, we obtain the diameter, girth, and the dominating number of $ \Gamma(G) $. We discuss the planarity and outer planarity for $ \Gamma(G) $. Finally, we prove that if $ p $ and $ q $ are distinct prime numbers and $ n = pq^k $, where $ p < q $ and $ k\geq 1 $, then $ \Gamma(D_{2n}) $ is not Hamiltonian.

Reaction of LiOCtBu2Ph with TlPF6 forms the dimeric Tl2(OCtBu2Ph)2 complex, a rare example of a homoleptic thallium alkoxide complex demonstrating formally two-coordinate metal centers. Characterization of Tl2(OCtBu2Ph)2 by 1H and 13C NMR spectroscopy and X-ray crystallography reveals the presence of two isomers differing by the mutual conformation of the alkoxide ligands, and by the planarity of the central Tl–O–Tl–O plane. Tl2(OCtBu2Ph)2 serves as a convenient precursor to the formation of old and new [M(OCtBu2Ph)n] complexes (M = Cr, Fe, Cu, Zn), including a rare example of T-shaped Zn(OCtBu2Ph)2(THF) complex, which could not be previously synthesized using more conventional LiOR/HOR precursors. The reaction of [Ru(cymene)Cl2]2 with Tl2(OCtBu2Ph)2 results in the formation of a ruthenium(II) alkoxide complex. For ruthenium, the initial coordination of the alkoxide triggers C–H activation at the ortho-H of [OCtBu2Ph] which results in its bidentate coordination. In addition to Tl2(OCtBu2Ph)2, related Tl2(OCtBu2(3,5-Me2C6H3))2 was also synthesized, characterized, and shown to exhibit similar reactivity with iron and ruthenium precursors. Synthetic, structural, and spectroscopic characterizations are presented.

All polymer solar cells (APSCs) have attracted considerable attention due to their unique advantages such as flexibility and mechanical stability. However, their poor charge mobility and difficulty in accurately optimizing phase separation structures have limited their performance improvement. Here, we achieved a multilength scale morphology control of the molecular local orientation and component distribution of the J51:N2200 blend by adding a volatilizable solid additive Bipy to the blend. Since Bipy was more compatible with J51 than N2200, J51 could be enriched on the bottom surface. During thermal annealing, with evaporation of Bipy across the thin thickness direction, Bipy has more chance to contact N2200. The repulsive force between Bipy and NDI2OD units of N2200 enhanced the chain planarity of N2200 and the connectivity between crystalline lamellae. This dual role of Bipy in J51:N2200 contributes to increases of the charge mobility and more balanced charge transfer simultaneously. Meanwhile, the rate of charge recombination decreases and charge extraction increases which result in an efficient PCE of 8.73%.

Molecular engineering enabling reversible transformation between helical and planar conformations is described herein. Starting from easily available 2-(pyridin-2-yl)anilines and alkynes, a one-pot strategy is set up for the synthesis of aza[4]helicenes via two successive rhodium-catalyzed C–H activation/cyclizations. Helical pyrrolophenanthridiziniums can be transformed into planar conformations through the cleavage of acidic pyrrole N–H, leading to turn-off fluorescence. NMR spectra, single crystal X-ray diffraction and DFT calculations demonstrate that the formation of an intramolecular C–H⋯N hydrogen bond is beneficial to stabilize the pyrrole nitrogen anion of the planar molecule and provide increased planarity. The reversible conformation transformations can be finely adjusted by the electron-donating and -withdrawing groups on the π+-fused pyrrole skeleton in the physiological pH range, thus affording an opportunity for pH-controlled intracellular selective fluorescence imaging. Pyrrolophenanthridiziniums show turn-on fluorescence in lysosomes owing to the acidic environment of lysosomes and turn-off fluorescence out of lysosomes, indicating the occurrence of the deprotonation reaction outside lysosomes and the corresponding transformation from helical to planar conformations., One-pot synthesis of aza[4]helicenes is accomplished through two successive C–H activation/cyclizations, which exhibit on/off fluorescence switching through reversible transformation between helical and planar conformations.

Organic solar cells (OSCs) based on non-fullerene acceptor (NFA) Y6 have drawn tremendous attention due to the great progress in their power conversion efficiencies (PCEs). Recently, experimental researchers found that the performance of BTPT-4F (like Y6 but having different side alkyl chains and a shorter fused-ring skeleton simultaneously) based OSCs is much worse than that of Y6 based OSCs. However, it is still confusing how the individual change of the fused-ring skeleton length or side alkyl chains of Y6 affects the photovoltaic properties, especially molecular arrangements and electron mobility. Therefore, we have modelled possible molecular arrangements of Y6, BTPT-4F, and two new intermediate NFAs, named BTPTT-4F-C8 and BTPTT-4F-C12, to systematically study the effects. The computed results could explain the experiment well, and show that terminal/central side alkyl chains and the length of the fused-ring skeleton all have noticeable influences on molecular planarity and arrangements. The outputs also illustrate that extending the fused-ring skeleton can increase electron mobility more than engineering side alkyl chains, and high electron mobility mainly depends on the formation of close face-on stacking of end groups and overlapping of partially flat backbones. Last but not least, both BTPTT-4F-C12 and BTPTT-4F-C8 are superior to Y6 in dipole moment, absorption spectra, charge separation, and electron mobility.

In this text based on the 2018 Lonsdale lecture, beginning with early work by Kathleen Lonsdale, instructive examples are given of unusual and unexpected structures derived from X-ray crystallography, not all of which are genuine results., This feature article is derived from the author’s presentation of the Lonsdale lecture at the BCA Spring Meeting in 2018. One of the research results for which Kathleen Lonsdale is best known was her 1929 demonstration that the benzene ring in crystalline hexa­methyl­benzene is planar and has essentially hexagonal symmetry, resolving decades of dispute among organic chemists. More recent crystallographic studies of hexa­methyl­benzene have shown that there are actually small deviations from planarity. Such deviations for aromatic compounds may be due to electronic, steric, and/or intermolecular factors. Some substituted benzene molecules display remarkably large deviations, both from a planar ring structure and from regular hexagonal angular geometry around the ring. Starting from this specific connection with Kathleen Lonsdale’s research, a number of stories are recounted of structural distortions and deviations from expected results and explanations that have been suggested for them, across a wide range of chemical topics including macrocycles, metal clusters, unusual coordination geometry and isomerism. On the way we find genuine surprises and results that have led to new understanding, but also examples of poor experiments, misinterpretation of data, scientific bias and preconceived ideas, incompetence and even deliberate fraud. Some aspects of structure validation are discussed. While showcasing some interesting research in its own right, this account also serves an educational purpose.

Graphical abstract, The non-natural ethynylmethylpyridone C-nucleoside (W), a thymidine (T) analogue that can be incorporated in oligonucleotides by automated synthesis, has recently been reported to form a high fidelity base pair with adenosine (A) and to be well accommodated in B-DNA duplexes. The enhanced binding affinity for A of W, as compared to T, makes it an ideal modification for biotechnological applications, such as efficient probe hybridization for the parallel detection of multiple DNA strands. In order to complement the experimental study and rationalize the impact of the non-natural W nucleoside on the structure, stability and dynamics of DNA structures, we performed quantum mechanics (QM) calculations along with molecular dynamics (MD) simulations. Consistently with the experimental study, our QM calculations show that the A:W base pair has an increased stability as compared to the natural A:T pair, due to an additional CH-π interaction. Furthermore, we show that mispairing between W and guanine (G) causes a distortion in the planarity of the base pair, thus explaining the destabilization of DNA duplexes featuring a G:W pair. MD simulations show that incorporation of single or multiple consecutive A:W pairs in DNA duplexes causes minor changes to the intra- and inter-base geometrical parameters, while a moderate widening/shrinking of the major/minor groove of the duplexes is observed. QM calculations applied to selected stacks from the MD simulations also show an increased stacking energy for W, over T, with the neighboring bases.

Interfacial charge-transfer is the critical process during the operation of dye-sensitized solar cells, determining the photovoltaic performance of the cell. Interfacial charge-transfer processes a...

As demonstrated in previous spectroscopic studies of 1,3-dioxole [ J. Am. Chem. Soc., 1993, 115, 12132-12136] and 1,3-benzodioxole [ J. Am. Chem. Soc., 1999, 121, 5056-5062], analysis of the ring-puckering potential energy function (PEF) of a "pseudo-four-membered ring" molecule can provide insight into understanding the magnitude of the anomeric effect. In the present study, high-level CCSD/cc-pVTZ and somewhat lower-level MP2/cc-pVTZ ab initio computations have been utilized to calculate the PEFs for 1,3-dioxole and 1,3-benzodioxole and 10 related molecules containing sulfur and selenium atoms and possessing the anomeric effect. The potential energy parameters derived for the PEFs directly provide a comparison of the relative magnitudes of the anomeric effect for molecules possessing OCO, OCS, OCSe, SCS, SCSe, and SeCSe linkages. The torsional potential energies produced by the anomeric effect for these linkages were estimated to range from 5.97 to 1.91 kcal/mol. The ab initio calculations also yielded the structural parameters, barriers to planarity, and ring-puckering angles for each of the 12 molecules studied. Based on the refined structural parameters for 1,3-dioxole and 1,3-benzodioxole, improved PEFs for these molecules were also calculated. The calculations also support the conclusion that the relatively low barrier to planarity of 1,3-benzodioxole results from competitive interactions between its benzene ring and the oxygen atom p orbitals.

Many of the process steps used in semiconductor chip manufacturing require planar (smooth) surfaces on the wafer to ensure correct pattern printing and generation of multilevel interconnections in the chips during manufacturing. Chemical-mechanical polishing/planarization (CMP) is the primary process used to achieve these surface planarity requirements. Modeling of CMP processes allows users to detect and fix large surface planarity variations (hotspots) in the layout prior to manufacturing. Fixing hotspots before tape-out may significantly reduce turnaround time and the cost of manufacturing. Creating an accurate CMP model that takes into account complicated chemical and mechanical polishing mechanisms is challenging. Measured data analysis and extraction of erosion and dishing data from profile linescans from test chips are important steps in CMP model building. Measured linescans are often tilted and noisy, which makes the extraction of erosion and dishing data more difficult. The development and implementation of algorithms used to perform automated linescan analysis may significantly reduce CMP model building time and improve the accuracy of the models. In this work, an automated linescan analysis (ALSA) tool is presented that performs automated linescan delineation, test pattern separation, and automatic extraction of erosion and dishing values from linescan data.