Computed nucleus-independent chemical shifts (NICS), contour plots of isotropic magnetic shielding (IMS), and gauge-including magnetically induced current (GIMIC) plots suggest that polarization of ...the π-system of acridones may perturb the numbers and positions of Clar sextet rings. Decreasing numbers of Clar sextets are connected to experimental observations of a narrowing HOMO-LUMO gap and increased charge mobility in solid-state assemblies of quinacridone and epindolidione.
Magnetic evaluations of aromaticity suggest that hydrogen bonding interactions can perturb the Clar sextet characters of acridones, which have implications for their electronic properties.
A supramolecular 2pseudo-rotaxane containing a naphthalimide-based pillararene host and a spiropyran-based imidazole guest was synthesized and investigated in a semiaqueous solution with 90% water ...fraction. Upon UV exposure, the close-form structure of nonemissive spiropyran guest could be transformed into the open-form structure of red-emissive merocyanine guest reversibly, which was utilized as a monofluorophoric sensor to detect copper(II) and cyanide ions. Moreover, the naphthalimide host as an energy donor with green photoluminescence (PL) emission at 505 nm was complexed with the merocyanine guest as an energy acceptor with red PL emission at 650 nm in 1:1 molar ratio to generate a 2pseudo-rotaxane polymer, which was further verified by the diffusion coefficients of DOSY nuclear magnetic resonance (NMR) measurements. Due to the Förster resonance energy transfer (FRET) processes, the bifluorophoric 2pseudo-rotaxane produced more efficient ratiometric PL behavior to induce a stronger red PL emission than that of the monofluorophoric guest; therefore, the PL sensor responses of the supramolecular 2pseudo-rotaxane toward copper(II) and cyanide ions could be further amplified via the FRET-OFF processes to turn off red PL emission of the reacted merocyanine acceptor and to recover green PL emission of the naphthalimide donor. Accordingly, the best and prominent values of the limit of detection (LOD) for the host–guest detections toward Cu2+ and CN– were 0.53 and 1.34 μM, respectively. The highest red MC emission with the optimum FRET processes of 2pseudo-rotaxane was maintained around room temperature (20–40 °C) in wide pH conditions (pH = 3–13), which can be utilized in the cell viability tests to prove the nontoxic and remarkable biomarker of 2pseudo-rotaxane to detect Cu2+ and CN– in living cells. The developed FRET-OFF processes with ratiometric PL behavior of the bifluorophoric supramolecular 2pseudo-rotaxane polymer will open a new avenue to the future applications of chemo- and biosensors.
Deformable energy-harvesting devices that are self-repairable and possess broad working temperatures remain a challenge for autonomous flexible electronics. Herein, the self-healable, stretchable, ...and anti-freezing entirely gel-based triboelectric nanogenerator (TENG) with a wide working temperature range from − 40 to 80 °C is reported in this study. Initially, an electrode gel was prepared by mixing poly(lipoic acid) with supramolecular crosslinkers of Fe3+ and phytic acid (PA), and the conductive polymer poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) was added. Secondly, a triboelectric gel was synthesized using amino- and hydroxy-terminated poly(dimethylsiloxane) (PDMS) along with isophorone diisocyanate and silicone oil. These gel networks were constructed by supramolecular interactions of reversible physical bonds and able to contribute high stretchability up to 50 times strain with fast self-healability (4 min for electrode gel and 24 h for tribolayer gel). The resulting gel-based TENG maintained excellent performance even after 5000 cyclic operations and showed stable performance after multiple cut/self-healing processes. Its outputs were increased as it was biaxially stretched up to 150% strain to retain its elasticity, ensuring its applicability in flexible uses. Moreover, the energy-harvesting capability was verified to be applicable from − 40 to 80 °C. Last, the gathered energy from the gel-based TENG was demonstrated to power up commercial electronics.
An entirely gel-based triboelectric nanogenerator (TENG) featuring self-healable, stretchable, and anti-freezing properties is presented. The device outputs are explored by cut/self-healing processes of three complete layers, biaxial stretching along with anti-freezing performances in a wide temperature range of − 40 to 80 °C. This gel-based TENG can serve as a power source for electronic devices (e.g., watch and calculator). Display omitted
•An entirely gel-based TENG with a wide working temperature range from − 40 to 80 °C is reported.•An electrode gel was prepared by mixing poly(lipoic acid) with supramolecular crosslinkers of Fe3+, PA, and PEDOT:PSS.•A triboelectric gel was synthesized using amino- and hydroxy-terminated PDMS along with IPDI and silicone oil.•The resulting gel-based TENG maintained excellent performance even after multiple cut/self-healing processes.•Its outputs were increased as it was biaxially stretched up to 150% strain, ensuring its applicability in flexible uses.
Dewar proposed the σ‐aromaticity concept to explain the seemingly anomalous energetic and magnetic behavior of cyclopropane in 1979. While a detailed, but indirect energetic evaluation in 1986 raised ...doubts—“There is no need to involve ‘σ‐aromaticity’,”—other analyses, also indirect, resulted in wide‐ranging estimates of the σ‐aromatic stabilization energy. Moreover, the aromatic character of “in‐plane”, “double”, and cyclically delocalized σ‐electron systems now seems well established in many types of molecules. Nevertheless, the most recent analysis of the magnetic properties of cyclopropane (S. Pelloni, P. Lazzeretti, R. Zanasi, J. Phys. Chem. A 2007, 111, 8163–8169) challenged the existence of an induced σ‐ring current, and provided alternative explanations for the abnormal magnetic behavior. Likewise, the present study, which evaluates the σ‐aromatic stabilization of cyclopropane directly for the first time, fails to find evidence for a significant energetic effect. According to ab initio valence bond (VB) computations at the VBSCF/cc‐PVTZ level, the σ‐aromatic stabilization energy of cyclopropane is, at most, 3.5 kcal mol−1 relative to propane, and is close to zero when n‐butane is used as reference. Trisilacyclopropane also has very little σ‐aromatic stabilization, compared to Si3H8 (6.3 kcal mol−1) and Si4H10 (4.2 kcal mol−1). Alternative interpretations of the energetic behavior of cyclopropane (and of cyclobutane, as well as their silicon counterparts) are supported.
The existence of σ aromaticity in cyclopropane (see picture) has been challenged by recent magnetic analysis. Ab initio valence bond computations reveal directly that the σ‐aromatic stabilization energy of cyclopropane is at most 3.5 kcal mol−1 relative to propane. This small energy difference raises the question whether there is any need to invoke the concept of σ aromaticity for cyclopropane.
Creating stimuli-responsive materials with switchable solid-state luminescence remains a challenge. We report that the solvation of a novel organic fluorophore can be utilized to prepare such a ...material, which emits in the blue (442-446 nm) region when wet and in the green (497-503 nm) region when dry.
Switchable solid-state fluorescence has been observed as a consequence of reversible solvation.
Aromaticity in transition structures Schleyer, Paul von Ragué; Wu, Judy I; Cossío, Fernando P ...
Chemical Society reviews,
07/2014, Letnik:
43, Številka:
14
Journal Article
Recenzirano
Aromaticity is an essential concept in chemistry, employed to account for the unusual stability, reactivity, molecular structures, and other properties of many unsaturated organic compounds. This ...concept was later extended to inorganic molecules and to saturated systems with mobile electrons, as well as to transition structures, the focus of the present review. Although transition structures are inherently delocalized, not all exhibit aromaticity. We contrast here examples of pericyclic reaction transition structures (where aromaticity is significant) with those for illustrative pseudo-pericyclic reactions (where aromaticity is less or not important). Non-pericyclic reactions may also have aromatic transition structures. State-of-the-art computational methods to evaluate the aromaticity of transition structures are described briefly.
This tutorial review presents interpretative computational tools to describe and quantify the different manifestations of aromaticity in transition structures.
The optical properties of stoichiometric iron pyrite (FeS2) nanocrystals (NCs) are characterized by strong UV-Visible (UV-Vis) absorption within the cutoff while negligible absorption beyond the ...cutoff in near-infrared and longer wavelengths. Herein, we show this bandgap limitation can be broken through controllable synthesis of nonstoichiometric Fe1- xS2 NCs ( x = 0.01-0.107) to induce localized surface plasmonic resonance (LSPR) absorption beyond the cutoff to short-wave infrared spectrum (SWIR, 1-3 μm) with remarkably enhanced broadband absorption across UV-Vis-SWIR spectra. To illustrate the benefit of the broadband absorption, colloidal LSPR Fe1- xS2 NCs were printed on graphene to form LSPR Fe1- xS2 NCs/graphene heterostructure photodetectors. Extraordinary photoresponsivity in exceeding 4.32 × 106 A/W and figure-of-merit detectivity D* > 7.50 × 1012 Jones have been demonstrated in the broadband of UV-Vis-SWIR at room temperature. These Fe1- xS2 NCs/graphene heterostructures are printable and flexible and therefore promising for practical optical and optoelectronic applications.
Description of Aromaticity in Porphyrinoids Wu, Judy I; Fernández, Israel; Schleyer, Paul v. R
Journal of the American Chemical Society,
01/2013, Letnik:
135, Številka:
1
Journal Article
Recenzirano
Like the larger nonplanar Möbius rings, porphyrinoid aromaticity is not due primarily to the macrocyclic π conjugation of the corresponding annulene perimeters. The block-localized wave function ...(BLW)-derived aromatic stabilization energies (ASE) of several porphyrinoids reveal that, on a per atom basis, the appended 6π electron heterocycles of porphyrinoids confer aromaticity much more effectively than the macrocyclic 4n+2 π electron conjugations. There is no direct relationship between thermochemical stability of porphyrinoids and their macrocyclic 4n or 4n+2 π electron counts. Porphyrinoids having an “antiaromatic” macrocyclic 4n+2 π electron conjugation pathway (e.g., 4) as well as those having no macrocyclic conjugation (e.g., 9) can be stabilized by aromaticity. Computed nucleus independent chemical shifts (NICS) and the anisotropy of the induced current density (ACID) disclose the intricate local versus macrocyclic circulation interplay for several porphyrinoids.
The ability to alter optoelectronic and magnetic properties of molecules at a late stage in their preparation is in general a nontrivial feat. Here, we report the late-stage oxidation of ...benzothiophene-fused indacenes and dicyclopentanaphthalenes to their corresponding sulfone derivatives. We find that while such modifications increase the highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) energy gap to a small degree, other properties such as HOMO and LUMO energy levels, molecule paratropicity, and singlet-triplet energy gaps are influenced to a greater degree. The most surprising finding is a change of the bond alternation pattern within the s-indacene core of the sulfones. Computations corroborate the experimental findings and offer plausible explanations for these changes in molecular properties.
A combined computational and experimental study reveals that
ortho
-,
meta
- and
para
-aminobiphenyl isomers undergo distinctly different photochemical reactions involving proton transfer. Deuterium ...exchange experiments show that the
ortho
-isomer undergoes a facile photoprotonation at a carbon atom
via
excited-state intramolecular proton transfer (ESIPT). The
meta
-isomer undergoes water-assisted excited-state proton transfer (ESPT) and a photoredox reaction
via
proton-coupled electron transfer (PCET). The
para
-isomer undergoes a water-assisted ESPT reaction. All three reactions take place in the singlet excited-state, except for the photoredox process of the
meta
-isomer, which involves a triplet excited-state. Computations illustrate the important role of excited-state antiaromaticity relief in these photoreactions.
ortho
-,
meta
- and
para
-aminobiphenyl isomers undergo distinctly different photochemical reactions involving proton transfer, which are driven by excited-state antiaromaticity relief.
