共查询到20条相似文献,搜索用时 31 毫秒
1.
Efficient photoswitching in the solid-state remains rare, yet is highly desirable for the design of functional solid materials. In particular, for molecular solar thermal energy storage materials high conversion to the metastable isomer is crucial to achieve high energy density. Herein, we report that 4-methoxyazobenzene (MOAB) can be occluded into the pores of a metal–organic framework Zn2(BDC)2(DABCO), where BDC = 1,4-benzenedicarboxylate and DABCO = 1,4-diazabicyclo[2.2.2]octane. The occluded MOAB guest molecules show near-quantitative E → Z photoisomerization under irradiation with 365 nm light. The energy stored within the metastable Z-MOAB molecules can be retrieved as heat during thermally-driven relaxation to the ground-state E-isomer. The energy density of the composite is 101 J g−1 and the half-life of the Z-isomer is 6 days when stored in the dark at ambient temperature.4-Methoxyazobenzene can be occluded into the pores of a MOF and show near-quantitative E → Z photoisomerization under irradiation with 365 nm light. The energy density of the composite is 101 J g−1 and the half-life of the Z-isomer is 6 days. 相似文献
2.
The chromophore of the green fluorescent protein (GFP) is critical for probing environmental influences on fluorescent protein behavior. Using the aqueous system as a bridge between the unconfined vacuum system and a constricting protein scaffold, we investigate the steric and electronic effects of the environment on the photodynamical behavior of the chromophore. Specifically, we apply ab initio multiple spawning to simulate five picoseconds of nonadiabatic dynamics after photoexcitation, resolving the excited-state pathways responsible for internal conversion in the aqueous chromophore. We identify an ultrafast pathway that proceeds through a short-lived (sub-picosecond) imidazolinone-twisted (I-twisted) species and a slower (several picoseconds) channel that proceeds through a long-lived phenolate-twisted (P-twisted) intermediate. The molecule navigates the non-equilibrium energy landscape via an aborted hula-twist-like motion toward the one-bond-flip dominated conical intersection seams, as opposed to following the pure one-bond-flip paths proposed by the excited-state equilibrium picture. We interpret our simulations in the context of time-resolved fluorescence experiments, which use short- and long-time components to describe the fluorescence decay of the aqueous GFP chromophore. Our results suggest that the longer time component is caused by an energetically uphill approach to the P-twisted intersection seam rather than an excited-state barrier to reach the twisted intramolecular charge-transfer species. Irrespective of the location of the nonadiabatic population events, the twisted intersection seams are inefficient at facilitating isomerization in aqueous solution. The disordered and homogeneous nature of the aqueous solvent environment facilitates non-selective stabilization with respect to I- and P-twisted species, offering an important foundation for understanding the consequences of selective stabilization in heterogeneous and rigid protein environments.Simulations on the aqueous green fluorescent protein (GFP) chromophore (in the equilibrium and non-equilibrium regimes) reveal that observed biexponential fluorescence originates from two competing torsional deactivation pathways. 相似文献
3.
Cheng Chen Jasmine N. Tutol Longteng Tang Liangdong Zhu Whitney S. Y. Ong Sheel C. Dodani Chong Fang 《Chemical science》2021,12(34):11382
Natural and laboratory-guided evolution has created a rich diversity of fluorescent protein (FP)-based sensors for chloride (Cl−). To date, such sensors have been limited to the Aequorea victoria green fluorescent protein (avGFP) family, and fusions with other FPs have unlocked ratiometric imaging applications. Recently, we identified the yellow fluorescent protein from jellyfish Phialidium sp. (phiYFP) as a fluorescent turn-on, self-ratiometric Cl− sensor. To elucidate its working mechanism as a rare example of a single FP with this capability, we tracked the excited-state dynamics of phiYFP using femtosecond transient absorption (fs-TA) spectroscopy and target analysis. The photoexcited neutral chromophore undergoes bifurcated pathways with the twisting-motion-induced nonradiative decay and barrierless excited-state proton transfer. The latter pathway yields a weakly fluorescent anionic intermediate , followed by the formation of a red-shifted fluorescent state that enables the ratiometric response on the tens of picoseconds timescale. The redshift results from the optimized π–π stacking between chromophore Y66 and nearby Y203, an ultrafast molecular event. The anion binding leads to an increase of the chromophore pKa and ESPT population, and the hindrance of conversion. The interplay between these two effects determines the turn-on fluorescence response to halides such as Cl− but turn-off response to other anions such as nitrate as governed by different binding affinities. These deep mechanistic insights lay the foundation for guiding the targeted engineering of phiYFP and its derivatives for ratiometric imaging of cellular chloride with high selectivity.We discovered an interplay between proton transfer and conformational reorganization that powers a standalone fluorescent-protein-based excitation-ratiometric biosensor for chloride imaging. 相似文献
4.
Matthew J. Evans Mathew D. Anker Claire L. McMullin Samuel E. Neale Nasir A. Rajabi Martyn P. Coles 《Chemical science》2022,13(16):4635
Multiply-bonded main group metal compounds are of interest as a new class of reactive species able to activate and functionalize a wide range of substrates. The aluminium sulfido compound K[Al(NONDipp)(S)] (NONDipp = [O(SiMe2NDipp)2]2−, Dipp = 2,6-iPr2C6H3), completing the series of [Al(NONDipp)(E)]− anions containing Al–E{16} multiple bonds (E{16} = O, S, Se, Te), was accessed via desulfurisation of K[Al(NONDipp)(S4)] using triphenylphosphane. The crystal structure showed a tetrameric aggregate joined by multiple K⋯S and K⋯π(arene) interactions that were disrupted by the addition of 2.2.2-cryptand to form the separated ion pair, [K(2.2.2-crypt)][Al(NONDipp)(S)]. Analysis of the anion using density functional theory (DFT) confirmed multiple-bond character in the Al–S group. The reaction of the sulfido and selenido anions K[Al(NONDipp)(E)] (E = S, Se) with CO2 afforded K[Al(NONDipp)(κ2E,O-EC{O}O)] containing the thio- and seleno-carbonate groups respectively, consistent with a [2 + 2]-cycloaddition reaction and C–E bond formation. An analogous cycloaddition reaction took place with benzophenone affording compounds containing the diphenylsulfido- and diphenylselenido-methanolate ligands, [κ2E,O-EC{O}Ph2]2−. In contrast, when K[Al(NONDipp)(E)] (E = S, Se) was reacted with benzaldehyde, two equivalents of substrate were incorporated into the product accompanied by formation of a second C–E bond and complete cleavage of the Al–E{16} bonds. The products contained the hitherto unknown κ2O,O-thio- and κ2O,O-seleno-bis(phenylmethanolate) ligands, which were exclusively isolated as the cis-stereoisomers. The mechanisms of these cycloaddition reactions were investigated using DFT methods.Reaction of Al–E (E = S, Se) multiple bonds with C O functionalities generates new C–E bonds. 相似文献
5.
Yi Liu Haojie Xu Xitao Liu Shiguo Han Wuqian Guo Yu Ma Qingshun Fan Xinxin Hu Zhihua Sun Junhua Luo 《Chemical science》2022,13(45):13499
Molecular antiferroelectrics (AFEs) have taken a booming position in the miniaturization of energy storage devices due to their low critical electric fields. However, regarding intrinsic competitions between dipolar interaction and steric hindrance, it is a challenge to exploit room-temperature molecular AFEs with high energy storage efficiency. Here, we present a new 2D hybrid perovskite-type AFE, (i-BA)2(FA)Pb2Br7 (1), which shows ultrahigh energy storage efficiencies at room temperature. Most strikingly, the typical double P–E hysteresis loops afford an ultrahigh storage efficiency up to ∼91% at low critical electric fields (Ecr = 41 kV cm−1); this Ecr value is much lower than those of state-of-the-art AFE oxides, revealing the potential of 1 for miniaturized energy-storage devices. In terms of the energy storage mechanism, the dynamic ordering and antiparallel reorientation of organic cations trigger its AFE-type phase transition at 303 K, thus giving a large spontaneous electric polarization of ∼3.7 μC cm−2, while the increasement of steric hindrance of the organic branched-chain i-BA+ spacer cations stabilizes its antipolar sublattices. To the best of our knowledge, this exploration of achieving ultrahigh energy storage efficiency at such a low critical electric field is unprecedented in the AFE family, which paves a pathway for miniaturized energy storage applications.We report a room-temperature molecular AFE, (i-BA)2(FA)Pb2Br7, which shows ultrahigh η of ∼91% at quite low electric fields. This finding will be advantageous to the progress of high energy-storage applications. 相似文献
6.
Chen Chen Meng-hui Wang Lin-Yan Feng Lian-Qing Zhao Jin-Chang Guo Hua-Jin Zhai Zhong-hua Cui Sudip Pan Gabriel Merino 《Chemical science》2022,13(27):8045
The occurrence of planar hexacoordination is very rare in main group elements. We report here a class of clusters containing a planar hexacoordinate silicon (phSi) atom with the formula SiSb3M3+ (M = Ca, Sr, Ba), which have D3h (1A1′) symmetry in their global minimum structure. The unique ability of heavier alkaline-earth atoms to use their vacant d atomic orbitals in bonding effectively stabilizes the peripheral ring and is responsible for covalent interaction with the Si center. Although the interaction between Si and Sb is significantly stronger than the Si–M one, sizable stabilization energies (−27.4 to −35.4 kcal mol−1) also originated from the combined electrostatic and covalent attraction between Si and M centers. The lighter homologues, SiE3M3+ (E = N, P, As; M = Ca, Sr, Ba) clusters, also possess similar D3h symmetric structures as the global minima. However, the repulsive electrostatic interaction between Si and M dominates over covalent attraction making the Si–M contacts repulsive in nature. Most interestingly, the planarity of the phSi core and the attractive nature of all the six contacts of phSi are maintained in N-heterocyclic carbene (NHC) and benzene (Bz) bound SiSb3M3(NHC)6+ and SiSb3M3(Bz)6+ (M = Ca, Sr, Ba) complexes. Therefore, bare and ligand-protected SiSb3M3+ clusters are suitable candidates for gas-phase detection and large-scale synthesis, respectively.The global minimum of SiSb3M3+ (M = Ca, Sr, Ba) is a D3h symmetric structure containing an elusive planar hexacoordinate silicon (phSi) atom. Most importantly, the phSi core remains intact in ligand protected environment as well.Exploring the bonding capacity of main-group elements (such as carbon or silicon) beyond the traditional tetrahedral concept has been a fascinating subject in chemistry for five decades. The 1970 pioneering work of Hoffmann and coworkers1 initiated the field of planar tetracoordinate carbons (ptCs), or more generally, planar hypercoordinate carbons. The past 50 years have witnessed the design and characterization of an array of ptC and planar pentacoordinate carbon (ppC) species.2–14 However, it turned out to be rather challenging to go beyond ptC and ppC systems. The celebrated CB62− cluster and relevant species15,16 were merely model systems because C avoids planar hypercoordination in such systems.17,18 In 2012, the first genuine global minimum D3h CO3Li3+ cluster was reported to have six interactions with carbon in planar form, although electrostatic repulsion between positively charged phC and Li centers and the absence of any significant orbital interaction between them make this hexacoordinate assignment questionable.19 It was only very recently that a series of planar hexacoordinate carbon (phC) species, CE3M3+ (E = S–Te; M = Li–Cs), were designed computationally by the groups of Tiznado and Merino (Fig. 1; left panel),20 in which there exist pure electrostatic interactions between the negative Cδ− center and positive Mδ+ ligands. These phC clusters were achieved following the so-called “proper polarization of ligand” strategy.Open in a separate windowFig. 1The pictorial depiction of previously reported phC CE3M3+ (E = S–Te; M = Li–Cs) clusters and the present SiE3M3+ (E = S–Te and N–Sb; M = Li–Cs and Ca–Ba) clusters. Herein the solid and dashed lines represent covalent and ionic bonding, respectively. The opposite double arrows illustrate electrostatic repulsion.The concept of planar hypercoordinate carbons has been naturally extended to their next heavier congener, silicon-based systems. Although the steric repulsion between ligands decreases due to the larger size, the strength of π- and σ-bonding between the central atom and peripheral ligands dramatically decreases, which is crucial for stability. Planar tetracoordinate silicon (ptSi) was first experimentally observed in a pentaatomic C2v SiAl4− cluster by Wang and coworkers in 2000.21 Very recently, this topic got a huge boost by the room-temperature, large-scale syntheses of complexes containing a ptSi unit.22 A recent computational study also predicted the global minimum of SiMg4Y− (Y = In, Tl) and SiMg3In2 to have unprecendented planar pentacoordinate Si (ppSi) units.23 Planar hexacoordinate Si (phSi) systems seem to be even more difficult to stabilize. Previously, a C2v symmetric Cu6H6Si cluster was predicted as the true minimum,24 albeit its potential energy surface was not fully explored. A kinetically viable phSi SiAl3Mg3H2+ cluster cation was also predicted.25 However, these phSi systems24,25 are only local minima and not likely to be observed experimentally. In 2018, the group of Chen identified the Ca4Si22− building block containing a ppSi center and constructed an infinite CaSi monolayer, which is essentially a two-dimensional lattice of the Ca4Si2 motif.26 Thus, it is still an open question to achieve a phSi atom to date.Herein we have tried to find the correct combination towards a phSi system as the most stable isomer. Gratifyingly, we found a series of clusters, SiE3M3+ (E = N, P, As, Sb; M = Ca, Sr, Ba), having planar D3h symmetry with Si at the center of the six membered ring, as true global minimum forms. Si–E bonds are very strong in all the clusters, and alkaline-earth metals interact with the Si center by employing their d orbitals. However, electrostatic repulsion originated from the positively charged Si and M centers for E = N, P, and As dominates over attractive covalent interaction, making individual Si–M contacts repulsive in nature. This makes the assignment of SiE3M3+ (E = N, P, As; M = Ca, Sr, Ba) as genuine phSi somewhat skeptical. SiSb3M3+ (M = Ca, Sr, Ba) clusters are the sole candidates which possess genuine phSi centers as both electrostatic and covalent interactions in Si–M bonds are attractive. The d orbitals of M ligands play a crucial role in stabilizing the ligand framework and forming covalent bonds with phSi. Such planar hypercoordinate atoms are, in general, susceptible to external perturbations. However, the present title clusters maintain the planarity and the attractive nature of the bonds even after multiple ligand binding at M centers in SiSb3M3(NHC)6+ and SiSb3M3(Bz)6+. This would open the door for large-scale synthesis of phSi as well.Two major computational efforts were made before reaching our title phSi clusters. The first one is to examine SiE3M3+ (E = S–Po; M = Li–Cs) clusters, which adopt D3h or C3v structures as true minima (see Table S1 in ESI†), being isoelectronic to the previous phC CE3M3+ (E = S–Po; M = Li–Cs) clusters. In the SiE3M3+ (E = S–Po; M = Li–Cs) clusters, the Si center always carries a positive charge ranging from 0.01 to +1.03|e|, in contrast to the corresponding phC species (see Fig. 1). Thus, electrostatic interactions between the Siδ+ and Mδ+ centers would be repulsive (Fig. 1). Given that the possibility of covalent interaction with an alkali metal is minimal, it would be a matter of debate whether they could be called true coordination. A second effort is to tune the electronegativity difference between Si and M centers so that the covalent contribution in Si–M bonding becomes substantial. Along this line, we consider the combinations of SiE3M3+ (E = N, P, As, Sb; M = Be, Mg, Ca, Sr, Ba). The results in Fig. S1† show that for E = Be and Mg, the phSi geometry has a large out-of-plane imaginary frequency mode, which indicates a size mismatch between the Si center and peripheral E3M3 (E = N–Bi; M = Be, Mg) ring. On the other hand, the use of larger M = Ca, Sr, Ba atoms effectively expands the size of the cavity and eventually leads to perfect planar geometry with Si atoms at the center as minima. In the case of SiBi3M3+, the planar isomer possesses a small imaginary frequency for M = Ca. Although planar SiBi3Sr3+ and SiBi3Ba3+ are true minima, they are 2.2 and 2.5 kcal mol−1 higher in energy than the lowest energy isomer, respectively (Fig. S2†). Fig. 2 displays some selected low-lying isomers of SiE3M3+ (E = N, P, As, Sb; M = Ca, Sr, Ba) clusters (see Fig. S3–S6† for additional isomers). The global minimum structure is a D3h symmetric phSi with an 1A1′ electronic state for all the twelve cases. The second lowest energy isomer, a ppSi, is located more than 49 kcal mol−1 above phSi for E = N. This relative energy between the most stable and nearest energy isomer gradually decreases upon moving from N to Sb. In the case of SiSb3M3+ clusters, the second-lowest energy isomer is 4.6–6.1 kcal mol−1 higher in energy than phSi. The nearest triplet state isomer is very high in energy (by 36–53 kcal mol−1, Fig. S3–S6†) with respect to the global minimum.Open in a separate windowFig. 2The structures of low-lying isomers of SiE3M3+ (E = N, P, As, Sb; M = Ca, Sr, Ba) clusters. Relative energies (in kcal mol−1) are shown at the single-point CCSD(T)/def2-TZVP//PBE0/def2-TZVP level, followed by a zero-energy correction at PBE0. The values from left to right refer to Ca, Sr, and Ba in sequence. The group symmetries and electronic states are also given.Born–Oppenheimer molecular dynamics (BOMD) simulations at room temperature (298 K), taking SiE3Ca3+ clusters as case studies, were also performed. The results are displayed in Fig. S7.† All trajectories show no isomerization or other structural alterations during the simulation time, as indicated by the small root mean square deviation (RMSD) values. The BOMD data suggest that the global minimum also has reasonable kinetic stability against isomerization and decomposition.The bond distances, natural atomic charges, and bond indices for SiE3Ca3+ clusters are given in † for M = Sr, Ba). The Si–E bond distances are shorter than the typical Si–E single bond distance computed using the self-consistent covalent radii proposed by Pyykkö.27 In contrast, the Si–M bond distance is almost equal to the single bond distance. This gives the first hint of the presence of covalent bonding therein. However, the Wiberg bond indices (WBIs) for the Si–M links are surprisingly low (0.02–0.04). We then checked the Mayer bond order (MBO), which can be seen as a generalization of WBIs and is more acceptable since the approach of WBI calculations assumes orthonormal conditions of basis functions while the MBO considers an overlap matrix. The MBO values for the Si–M links are now sizable (0.13–0.18). These values are reasonable considering the large difference in electronegativity between Si and M, and, therefore, only a very polar bond is expected between them. In fact, the calculations of WBIs after orthogonalization of basis functions by the Löwdin method gives significantly large bond orders (0.48–0.55), which is known to overestimate the bond orders somewhat. The above results indicate that the presence of covalent bonding cannot be ruled out only by looking at WBI values.Bond distances (r, in Å), different bond orders (WBIs) {MBOs} [WBI in orthogonalized basis], and natural atomic charges (q, in |e|) of SiE3Ca3+ (E = N, P, As, Sb) clusters at the PBE0/def2-TZVP level
Open in a separate windowOur following argument regarding the presence of covalent Si–M bonding is based on energy decomposition analysis (EDA) in combination with natural orbital for chemical valence (NOCV) theory. We first performed EDA by taking Ca and SiE3Ca2 in different charge and electronic states as interacting fragments to get the optimum fragmentation scheme that suits the best to describe the bonding situation (see Tables S6–S9†). The size of orbital interaction (ΔEorb) is used as a probe.28 For all cases, Ca+ (D, 4s1) and SiE3Ca2 (D) in their doublet spin states turn out to be the best schemes, which give the lowest ΔEorb value. Energy term Interaction Ca+ (D, 4s1) + SiN3Ca2 (D) Ca+ (D, 4s1) + SiP3Ca2 (D) Ca+ (D, 4s1) + SiAs3Ca2 (D) Ca+ (D, 4s1) + SiSb3Ca2 (D) ΔEint −192.9 −153.0 −144.9 −129.9 ΔEPauli 139.8 115.2 115.7 110.9 ΔEelstata −162.0 (48.7%) −116.4 (43.4%) −113.0 (43.4%) −100.9 (41.9%) ΔEorba −170.7 (51.3%) −151.8 (56.6%) −147.6 (56.6%) −140.0 (58.1%) ΔEorb(1)b SiE3Ca2–Ca+(s) electron-sharing σ-bond −89.2 (52.3%) −79.4 (52.3%) −74.3 (50.3%) −66.9 (47.8%) ΔEorb(2)b SiE3Ca2 → Ca+(d) π‖-donation −32.9 (19.3%) −32.0 (21.1%) −31.8 (21.5%) −30.8 (22.0%) ΔEorb(3)b SiE3Ca2 → Ca+(d) σ-donation −13.1 (7.7%) −11.9 (7.8%) −12.0 (8.1%) −11.9 (8.5%) ΔEorb(4)b SiE3Ca2 → Ca+(d) π⊥-donation −12.3 (7.2%) −12.2 (8.0%) −12.5 (8.5%) −12.5 (8.9%) ΔEorb(5)b SiE3Ca2 → Ca+(d) δ-donation −8.1 (4.7%) −9.9 (6.5%) −10.9 (7.4%) −11.8 (8.4%) ΔEorb(rest)b −15.1 (8.8%) −6.4 (4.2%) −6.1 (4.1%) −6.1 (4.4%)
r Si–E | r Si–Ca | r E–Ca | q Si | q E | q Ca | |
---|---|---|---|---|---|---|
E = N | 1.669 | 2.555 | 2.246 | 1.57 | −1.93 | 1.74 |
(1.14) {1.23} [1.84] | (0.02) {0.13} [0.51] | (0.22) {0.67} [0.84] | ||||
E = P | 2.180 | 2.935 | 2.640 | 0.25 | −1.42 | 1.67 |
(1.34) {1.11} [1.52] | (0.03) {0.14} [0.54] | (0.27) {0.74} [1.05] | ||||
E = As | 2.301 | 3.004 | 2.721 | 0.07 | −1.34 | 1.65 |
(1.33) {1.10} [1.45] | (0.03) {0.15} [0.55] | (0.29) {0.71} [1.12] | ||||
E = Sb | 2.538 | 3.155 | 2.896 | −0.39 | −1.16 | 1.62 |
(1.29) {1.01} [1.33] | (0.04) {0.18} [0.48] | (0.30) {0.78} [1.14] |