A series of multistimuli-responsive 2rotaxanes with a naphthalimide-functionalized macrocycle threaded through an axle containing a photochromic spiropyran (SP) or merocyanine (MC) stopper were ...fabricated and studied for their distinct photophysical properties in semiaqueous solutions. By different combinations of chemical and photochemical switchable stimuli, these 2rotaxanes could be interconverted between multiple states, including monofluorophoric 2rotaxanes with the close form of the SP unit, i.e., Rot-H-SP and Rot-SP before and after shuttling upon acid–base controls, respectively, along with their corresponding bifluorophoric 2rotaxanes possessing the open form of the MC unit, i.e., Rot-H-MC and Rot-MC after UV exposure. Interestingly, the photoinduced electron-transfer (PET) effects appeared between nonemissive SP and aggregation-caused quenching (ACQ) naphthalimide units in 2rotaxanes Rot-H-SP and Rot-SP, whereas the Förster resonance energy transfer (FRET)/Dexter energy transfer occurred in 2rotaxanes Rot-H-MC and Rot-MC between green-emissive naphthalimide donor (λem = 528 nm) and red-emissive MC acceptor (λem = 648 nm) moieties after UV exposure. Moreover, the PET as well as FRET/Dexter energy-transfer processes and the speculated molecular arrangements (with/without macrocyclic tilting) of all 2rotaxanes and related derivatives were verified by time-resolved photoluminescence (TRPL) measurements and theoretical studies. Among all 2rotaxanes and derivatives, Rot-MC in tetrahydrofuran (THF)/H2O (2:8, v/v) revealed the strongest red MC emission with the most effective FRET process that possessed attractive ratiometric photoluminescence (PL) due to the ideal shortest donor–acceptor distance. Regardless of pH and temperature effects, the highest red MC emissions with the optimum FRET processes of all compounds were maintained at room temperature in near-neutral conditions (i.e., pH = 5–9). Importantly, the red-emissive 2rotaxane Rot-MC showed high selectivity and sensitivity toward sulfite-ion sensing to recover green donor emission via FRET-OFF behavior owing to the Michael reaction of the MC moiety with the sulfite ion, which had an excellent limit of detection (LOD) value of 0.76 μM to be further utilized for the cellular imaging of sulfite detection in living cells. Accordingly, the novel ratiometric sensor approaches of bifluorophoric 2rotaxane systems have been well developed in this study as the first rotaxane application of FRET processes toward sulfite detection with higher sensitivities than those of their monofluorophoric analogues. Various LOD values could be evaluated to realize the sulfite-sensing mechanisms of well-designed 2rotaxane systems by the shuttling of macrocyclic fluorophores along with photoswitchable FRET behaviors via alternative UV–vis exposures.
Whether tetra‐tert‐butyl‐s‐indacene is a symmetric D2h structure or a bond‐alternating C2h structure remains a standing puzzle. Close agreement between experimental and computed proton chemical ...shifts based on minima structures optimized at the M06‐2X, ωB97X‐D, and M11 levels confirm a bond‐localized C2h symmetry, which is consistent with the expected strong antiaromaticity of TtB‐s‐indacene.
The structure of tetra‐tert‐butyl‐s‐indacene is a computational challenge. Highly correlated methods and popular DFT functionals predict a bond‐delocalized D2h symmetry, but excellent agreement between experimental and computed proton chemical shifts suggests a true C2h geometry.
We examine the effects of fusing two benzofurans to s‐indacene (indacenodibenzofurans, IDBFs) and dicyclopentab,gnaphthalene (indenoindenodibenzofurans, IIDBFs) to control the strong antiaromaticity ...and diradical character of these core units. Synthesis via 3‐functionalized benzofuran yields syn‐IDBF and syn‐IIDBF. syn‐IDBF possesses a high degree of paratropicity, exceeding that of the parent hydrocarbon, which in turn results in strong diradical character for syn‐IIDBF. In the case of the anti‐isomers, synthesized via 2‐substituted benzofurans, these effects are decreased; however, both derivatives undergo an unexpected ring‐opening reaction during the final dearomatization step. All the results are compared to the benzothiophene‐fused analogues and show that the increased electronegativity of oxygen in the syn‐fused derivatives leads to enhancement of the antiaromatic core causing greater paratropicity. For syn‐IIDBF increased diradical character results from rearomati‐zation of the core naphthalene unit in order to relieve this paratropicity.
Fusion of benzofuran to either s‐indacene or dicyclopentab,gnaphthalene results in two dramatically different outcomes depending upon heterocycle orientation. Whereas the “anti” isomers are unstable and hydrolyze readily to ring‐opened products, the “syn” isomers are quite stable and afford molecules that either possess a high degree of antiaromaticity or exhibit pronounced diradical character.
A novel type of substrate for quantitative surface enhanced Raman spectroscopy (SERS) composed of chemical vapor deposition (CVD) graphene and in-situ fabricated rounded gold nanoparticles (AuNPs) ...was designed. SERS was measured on samples of different concentrations of Rhodamine 6G (R6G) on the AuNPs/graphene substrates using a low power 632.8 nm laser. Finite element simulations were carried out for a system of two gold hemiellipsoids under various conditions such as with R6G analyte covering the surface and with graphene underneath the nanoparticles. Graphene or R6G being present between the two nanoparticles caused a redshift in the plasmonic resonance frequency, and the graphene dampened the electric field of the surface. Regardless of the weakened electric field, the synergy of the AuNPs and graphene still enhanced the Raman signature of R6G to a greater extent than the nanoparticles or graphene alone could, which is attributed to the charge transferring mechanism effect of graphene on SERS. The lowest concentration of solid phase R6G deposited in this manner that could be detected was 8 × 10−7 M. Higher analyte concentrations and the characteristic peak intensities of the analyte showed a logarithmic relation as anticipated from the plasmonically enhanced Raman scattering.
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The self-trapping nano-loop structures of 1rotaxanes exhibited multiple Förster resonance energy transfer (FRET) patterns
via
dual and sequential locking/unlocking of pH-gated and UV exposure ...processes. As a tightened and constrained nano-loop in the acidic condition, dithienylethene (DTE) unit was locked in the highly bending open form to forbid ring closure upon UV irradiation.
The self-trapping nano-loop structures of 1rotaxanes exhibited multiple Förster resonance energy transfer (FRET) OFF/ON patterns
via
dual and sequential locking/unlocking upon UV exposure.
The novel multistimuli-responsive monofluorophoric supramolecular polymer Poly(TPE-DBC)/FL-DBA and pseudo3rotaxane TPE-DBC/FL-DBA consisted of the closed form of nonemissive fluorescein guest ...FL-DBA along with TPE-based main-chain macrocyclic polymer Poly(TPE-DBC) and TPE-functionalized macrocycle TPE-DBC hosts, respectively. By the combination of various external stimuli, these fluorescent supramolecular host–guest systems could reveal interesting photoluminescence (PL) properties in DMF/H2O (1:1, v/v) solutions, including bifluorophoric host–guest systems after the complexation of Al3+ ion, i.e., TPE-DBC/FL-DBA-Al 3+ and Poly(TPE-DBC)/FL-DBA-Al 3+ with their corresponding open form of fluorescein guest FL-DBA-Al 3+ . Importantly, the Förster resonance energy transfer (FRET) processes occurred in both bifluorophoric host–guest systems between blue-emissive TPE donors (λem = 470 nm) and green-emissive fluorescein acceptors (λem = 527 nm) after aluminum detection, which were further verified by time-resolved photoluminescence (TRPL) measurements to acquire their FRET efficiencies of 40.4 and 31.1%, respectively. Both supramolecular host–guest systems exhibited stronger green fluorescein emissions as well as appealing ratiometric PL behaviors within the desirable donor–acceptor distances of FRET processes in comparison with their detached analogous mixtures. Regarding the pH effects, the optimum green fluorescein emissions with effective FRET processes of all compounds and host–guest systems were sustained in the range pH = 7–10. Interestingly, both host–guest systems TPE-DBC/FL-DBA and Poly(TPE-DBC)/FL-DBA possessed high sensitivities and selectivities toward aluminum ion to display their strong green emissions via FRET-ON behaviors due to the chelation-induced ring opening of spirolactam moieties to become green-emissive guest acceptor FL-DBA-Al 3+ , which offered excellent limit of detection (LOD) values of 50.61 and 38.59 nM, respectively, to be further applied for the fabrication of facile test strips toward aluminum detection. Accordingly, the inventive ratiometric PL and FRET sensor approaches of supramolecular host–guest systems toward aluminum ion with prominent sensitivities and selectivities were well-established in this study.
Two‐dimensional transition metal dichalcogenides (TMDs)/graphene van der Waals (vdW) heterostructures integrate the superior light–solid interaction in TMDs and charge mobility in graphene, and ...therefore are promising for surface‐enhanced Raman spectroscopy (SERS). Herein, a novel TMD (MoS2 and WS2) nanodome/graphene vdW heterostructure SERS substrate, on which an extraordinary SERS sensitivity is achieved, is reported. Using fluorescent Rhodamine 6G (R6G) as probe molecules, the SERS sensitivity is in the range of 10−11 to 10−12 m on the TMD nanodomes/graphene vdW heterostructure substrates using 532 nm Raman excitation, which is comparable to the best sensitivity reported so far using plasmonic metal nanostructures/graphene SERS substrates, and is more than three orders of magnitude higher than that on single‐layer TMD and graphene substrates. Density functional theory simulation reveals enhanced electric dipole moments and dipole–dipole interaction at the TMD/graphene vdW interface, yielding an effective means to facilitate an external electrostatic perturbation on the graphene surface and charge transfer. This not only promotes chemical enhancement on SERS, but also enables electromagnetic enhancement of SERS through the excitation of localized surface plasmonic resonance on the TMD nanodomes. This TMD nanodome/graphene vdW heterostructure is therefore promising for commercial applications in high‐performance optoelectronics and sensing.
The superior light–solid interaction in transition metal dichalcogenides (TMDs) and charge mobility in graphene are integrated in TMD nanodomes/graphene van der Waals heterostructures as a surface‐enhanced Raman spectroscopy (SERS) substrate. A Rhodamine 6G SERS sensitivity of 5 × 10‐12
m is demonstrated on these substrates. This enhancement is similar to the localized surface plasmonic resonance enhancement by metallic nanoparticles.
Manipulations of singlet oxygen (1O2) generations by the integration of both aggregation‐induced emission luminogen (AIEgen) photosensitizer and photochromic moieties have diversified features in ...photodynamic therapy applications. Through Förster resonance energy transfer (FRET) pathway to induce red PL emissions (at 595 nm) for 1O2 productions, 1rotaxane containing photosensitive tetraphenylethylene (TPE) donor and photochromic diarylethene (DAE) acceptor is introduced to achieve dual and sequential locked/unlocked photoswitching effects by pH‐controlled shuttling of its contracted/extended forms. Interestingly, the UV‐enabled DAE ring closure speeds follow the reversed trend of DAE self‐constraint degree as: contracted < extended < noninterlocked forms in 1rotaxane analogues, thus FRET processes can be adjusted in contracted/extended forms of 1rotaxane upon UV irradiations. Accordingly, the contracted form of 1rotaxane is FRET‐OFF locked and inert to UV exposure due to the larger bending conformation of DAE parallel (p‐)conformer, compared with its extended and noninterlocked analogues possessing switchable FRET‐OFF/ON behaviors activated by dual and sequential pH‐ and photoswitching. Owing to the advantages of 1O2 productions tuned by multistimuli inputs (pH, UV, and blue light), an useful logic circuit for toxicity outputs of the surface modified 1rotaxane nanoparticles (NPs) has been demonstrated to offer promising 1O2 productions and managements based on mechanically interlocked molecules for future bioapplications.
Through Förster resonance energy transfer (FRET) to induce red PL emissions and 1O2 productions, 1rotaxane containing a photosensitive tetraphenylethylene donor and a photochromic diarylethene (DAE) acceptor is introduced to achieve dual and sequential locked/unlocked photoswitching effects by pH‐controlled shuttling of its contracted/extended forms upon UV irradiations by following UV‐enabled DAE ring closure speeds of contracted < extended < noninterlocked forms.
Computed association strengths for 43 purine and pteridine quartets (38 to 100 kcal mol
−1
) show excellent linear correlation with π-conjugation gain in the assembled monomers (
r
2
= 0.965). Even ...quartets having the same secondary electrostatic interactions can display very different association strengths depending on the π-conjugation patterns of the monomeric units.
π-Conjugation patterns determine the association strengths of purine and pteridine quartets.
Aromaticity: Quo Vadis Merino, Gabriel; Solà, Miquel; Fernández, Israel ...
Chemical science,
05/2023, Letnik:
14, Številka:
21
Journal Article
Recenzirano
Odprti dostop
Aromaticity is one of the most deeply rooted concepts in chemistry. But why, if two-thirds of existing compounds can be classified as aromatic, is there no consensus on what aromaticity is? σ−, π−, ...δ−, spherical, Möbius, or all-metal aromaticity... why are so many attributes needed to specify a property? Is aromaticity a dubious concept? This perspective aims to reflect where the aromaticity community is and where it is going.
In this perspective, different expert opinions are gathered on the definition and concept of aromaticity.
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