2-anthracenecarboxylic Acid Research Articles

Supramolecular Architecture of an Amphiphilic Amino Alcohol as a Versatile Chiral Environment for Stereocontrolled Photoreaction of Various Anthracenes.

The photocyclodimerization of 2-anthracenecarboxylic acid has been extensively studied as a model reaction of asymmetric photochemistry. So far, numerous chiral environments have been employed to control this photoreaction, while the scope of photoreactants has been limited only to 2-anthracenecarboxylic acid and its simple esters and amides. Here, we developed a systematic series of photoreactants (2 a-d) by introducing various substituents to 2-anthracenecarboxylic acid, which showed different reactivities and selectivities depending on the substituents. By using the photoreactants 2 a-d, we evaluated the performance of a chiral environment composed of an amphiphilic amino alcohol (1), where the photocyclodimerization of 2 a-d generally proceeded in excellent regio- and enantioselectivities (71-98 % regio ratio, 76-86 % ee). Furthermore, by reacting 2 a and 2 b together in the chiral environment of 1, we succeeded in the first stereocontrolled cross-photocyclodimerization between two prochiral anthracenes (58 % chemo ratio, 83 % regio ratio, 90 % ee).

PH-Controlled enantioselectivity switching of irregular photodimers in photocyclodimerization of 2-anthracenecarboxylic acid mediated with β-cyclodextrin derivatives

β-CDx derivatives invert the stereochemical outcome of syn-head-to-tail-photodimers, upon changing solution pH, solving the problem of antipodal-chiral hosts not being available.

Supramolecular Enantiodifferentiating Photocyclodimerization of 2-Anthracenecarboxylic Acid Mediated by Bridged β-Cyclodextrins: Critical Effects of the Host Structure, pH and Co-Solvents.

Several sulfoxide- and sulfone-bridged β-cyclodextrin (CD) dimers were synthesized for mediating the enantiodifferentiating [4+4] photocyclodimerization of 2-anthracenecarboxylic acid (AC). The complexation behavior of these chiral hosts with AC was investigated by UV-vis, circular dichroism, fluorescence, and NMR spectroscopies and certified the formation of 1 : 1 and 1 : 2 host-guest complexes. The product distribution and enantioselectivity of the photoreaction turned out to be a critical function of the chemical structure of bridged CDs. Comparing to the sulfur-bridged 2AX -3GX β-CD dimer 7, the conversion of the photolyzes with sulfoxide-bridged was significantly improved, and the ee of cyclodimer 2 was remarkably increased from -82.8% with 7 to -96.7% with the sulfoxide-bridged 2AX -3GX β-CD dimer 8. The relative yields and ee values of the slipped cyclodimers 5 and 6 were greatly enhanced in the presence of 6 M CsCl. The reaction selectivity is susceptible to the pH variation of the aqueous buffer solution, demonstrating that the supramolecular photochirogenesis is controlled by multidimensional factors, including the chemical structure of the chiral host, solvent, and pH conditions.

Realizing Dynamic Diffraction Gratings Based on Light-Direct Writing of Responsive 2D Ordered Patterns

A dynamic diffraction grating (DDG) can realize on-demand in-situ regulation of light diffraction and is highly necessary in the next-generation optical devices; however, its fabrication remains challenging because of difficulties in generating a responsive pattern in the bulk material or on the surface. In this study, a facile and general approach to construct DDG is developed based on the near-infrared radiation (NIR)-driven responsive 2D ordered surface pattern, which is fabricated by light-direct writing of wrinkles on a thin film of a photosensitive supramolecular polymer network comprised of a copolymer containing amino groups, anthracene carboxylic acid (ANA), and carbon nanotubes. The resulting surface pattern, which exhibits a height dependence on the NIR irradiation, can be used as the DDG whose optical diffraction can be regulated in-situ by NIR. Furthermore, because of the presence of a reversible ANA photodimer and hydrogen bonding in the supramolecular network, the patterned surface can be erased and rewritten by UV light with different wavelengths and self-healed by NIR irradiation. The results demonstrate a simple strategy for DDGs that will have a broad application in the fields of optics, electronics, and intelligent sensing.

PH-Controlled Chirality Inversion in Enantiodifferentiating Photocyclodimerization of 2-Antharacenecarboxylic Acid Mediated by γ-Cyclodextrin Derivatives.

Several γ-cyclodextrin (γ-CDx) derivatives were used as chiral hosts for the photocyclodimerization of 2-anthracenecarboxylic acid (AC). The effect of pH on photoreactivity and stereochemical outcome of photoproducts was investigated. Upon changing the solution pH, the stereochemical outcome of HH cyclodimer 3 was inverted from 25.2% to -64.4% and 41.2% to -76.2%, respectively, in the photocyclodimerization of AC mediated by bis-quinoline-modified γ-CDx 7 and its N-methylated derivative 8.

A Study of Photoprocesses of 3,3'-Diethyl-5,5'-Dichlorothiacarbocyanine in Water and Methanol

Photoprocesses in 3,3'-diethyl-5,5'-dichlorothiacarbocyanine have been studied in the cases of direct and sensitized photoexcitation in methanol and water in the absence and in the presence of cucurbit[7]uril. Under laser pulse excitation, trans–cis isomerization occurring via the excited singlet state of the dye (S*) takes place preferentially. The population of the dye triplet T state increases in the sensitized excitation as a result of triplet–triplet energy transfer from a triplet energy donor (anthracene and anthracenecarboxylic acid) to the dye (acceptor). Deactivation of the molecules in the T state occurs via electron transfer and back Т→S* intersystem crossing. The S* state formed in the Т→S* process decays via both conventional and delayed fluorescence. The presence of cucurbit[7]uril in the dye aqueous solution does not affect the mechanism of the photoprocesses in the dye, but it facilitates dimerization and increase in the yield into the T state, mainly of the dimers, and increases the lifetime of the dye cis-isomers.

Enantioselective photoinduced cyclodimerization of a prochiral anthracene derivative adsorbed on helical metal nanostructures.

The generation of molecular chirality in the absence of any molecular chiral inductor is challenging and of fundamental interest for developing a better understanding of homochirality. Here, we show the manipulation of molecular chirality through control of the handedness of helical metal nanostructures (referred to as nanohelices) that are produced by glancing angle deposition onto a substrate that rotates in either a clockwise or counterclockwise direction. A prochiral molecule, 2-anthracenecarboxylic acid, is stereoselectively adsorbed on the metal nanohelices as enantiomorphous anti-head-to-head dimers. The dimers show either Si-Si or Re-Re facial stacking depending on the handedness of the nanohelices, which results in a specific enantiopreference during their photoinduced cyclodimerization: a left-handed nanohelix leads to the formation of (+)-cyclodimers, whereas a right-handed one gives (-)-cyclodimers. Density functional theory calculations, in good agreement with the experimental results, point to the enantioselectivity mainly arising from the selective spatial matching of either Si-Si or Re-Re facial stacking at the helical surface; it may also be influenced by chiroplasmonic effects.

Synergetic effects in the enantiodifferentiating photocyclodimerization of 2-anthracenecarboxylic acid mediated by β-cyclodextrin-pillar[5]arene-hybridized hosts.

Tri-cavity hosts consisting of one pillar[5]arene (P5) sandwiched by two β-cyclodextrins (CDs) were synthesized, and their diastereoseparation was successfully accomplished. Photocyclodimerization of 2-anthracenecarboxylate with these hybrid hosts demonstrated the critical dependence of stereoselectivity on the absolute configuration of the central P5 and the conjugating positions on the β-CD, and gave the non-classical HT photodimers in up to 87% ee.

Primary amines enhance triplet energy transfer from both the band edge and trap state from CdSe nanocrystals.

In this study, the role that primary amines play during triplet energy transfer from photoexcited CdSe nanocrystals (NCs) was examined. Colloidally synthesized CdSe NCs were placed in varying concentrations of 1-propyl- or 1-octylamine, with and without 2-anthracenecarboxylic acid transmitter ligands attached. This primary amine increases upconversion quantum yield approximately 5-fold. Further addition of amine does not improve photon upconversion, as CdSe NC photoluminescence (PL) increases at the expense of triplet energy transfer. Transient absorption measurements show that the amine plays three key roles. Primary amines enhance NC PL by decreasing the nonradiative decay rate, increase the rate of triplet energy transfer, and enable the broad trap state in these CdSe NCs to participate in triplet photosensitization.

Reversal of Regioselectivity during Photodimerization of 2-Anthracenecarboxylic Acid in a Water-Soluble Organic Cavitand.

The value of octa acid (OA) as a reaction vessel in steering a photoreaction toward a less favored product was established. Photodimerization of 2-anthracenecarboxylic acid within OA yields exclusively head-to-head dimers, while in media such as solution, cyclodextrins (CD) and related hosts yield predominantly head-to-tail dimers. Further, OA enhances the chiral selectivity on the product dimers. The difference between OA and CD is attributed to the variation in the dimensions of their entry ports.

Effects of Temperature and Host Concentration on the Supramolecular Enantiodifferentiating [4 + 4] Photodimerization of 2-Anthracenecarboxylate through Triplet-Triplet Annihilation Catalyzed by Pt-Modified Cyclodextrins.

Visible-light-driven photocatalytic supramolecular enantiodifferentiating dimerization of 2-anthracenecarboxylic acid (AC) through triplet-triplet annihilation (TTA), mediated by the Schiff base Pt(II) complex (Pt-1, Pt-2, and Pt-3) was studied. The host concentration and the temperature effects on the stereoselectivity were comprehensively investigated. Increasing the concentration of sensitizers/hosts significantly enhanced the conversion of the photoreaction but led to reduced enantioselectivities of the chiral photodimers 2 and 3 when the photoreaction was triggered by a 532 nm laser, which was in contrast with the results obtained by direct irradiation of AC with a 365 nm light-emitting diode (LED) lamp, due to the aggregation of the sensitizer/host in water. The cyclization of AC through triplet-triplet annihilation displayed significant temperature dependency when Pt-3 was employed as the sensitizer/host. Increasing the temperature from 0 °C to 30 °C with 5% equiv. of Pt-3 led to a great increase of the ee of 2 from 2.1% to 31.6%. However, hardly any temperature dependency was observed when the photodimerization was mediated by other sensitizers and/or hosts, or the photoreaction was triggered directly with a 365 nm LED lamp.

Enhanced irregular photodimers and switched enantioselectivity by solvent and temperature in the photocyclodimerization of 2-anthracenecarboxylate with modified β-cyclodextrins

A series of primary-face- or secondary-face-modified β-cyclodextrins (CDs) 7-11 were prepared for mediating the enantiodifferentiating [4 + 4] photocyclodimerization reactions of 2-anthracenecarboxylic acid (AC). The complexation behavior of these hosts with AC was studied by 1H NMR, UV–vis, circular dichroism spectroscopy and ITC titration. The product distribution and product’s ee turned out to be a critical function of the skeleton and periphery modifications of β-CD. The combined yields of slipped cyclodimers 5 and 6 were greatly enhanced in the presence of modified β-CDs. In contrast to native β-CD and other β-CD derivatives, host 9, in which a phenyltriazolyl group was introduced on the primary face of β-CD, afforded antipodal cyclodimer 6 in a much higher enantioselectivity of 46% ee. The influence of temperature and salt additives were investigated in depth. Intriguingly, product chirality was switched by temperature in the presence of 6 M CsCl. Under an optimized condition, host 8 gave slipped cyclodimer 6 in 70% ee, which is the highest enantioselectivity ever reported for the slipped cyclodimer.

Galvanic Replacement of Chiral Hosts for Generating Helical Nanoparticles with Engineerable Compositions and Optical Activity

Metallic helices with a characteristic helical pitch (P) in the micro- or nano-scale have been proposed to develop diverse chirality-related primary applications. However, limit development of nanofabrication techniques leads to P > 20 nm; molecules are too small in size to effectively perceive the helical chirality, and such the dimensional mismatch will substantially prohibit the development of those applications. Currently, we devise glancing angle deposition (GLAD) with fast substrate rotation to successfully generate metallic helical nanoparticles (HNPs) with a sub-10-nm P. The sub-10-nm P is compatible with the molecular scale, such that we use the sub-10-nm-P HNPs to amplify optical activity of enantiomers that are grafted on the HNPs in roughly one order of magnitude, and to effectively mediate the enantioselective photocyclodimerization of 2-Anthracenecarboxylic acid. However, GLAD is operated at an extremely oblique deposition angle of > 85° with respect to the direction of substrate normal, resulting in an evidently low deposition yield given that most of evaporated atoms will not condense on the substrate. From the production cost point of view, low deposition yield tends to severely limit the application of such the technique to generate HNPs made of noble metals, which typically function as heterogeneous asymmetric catalysts. It is of practical demand on developing an economic method to produce noble metal HNPs with high production yield. In this talk, we will present a two-step fabrication of noble metal HNPs, composed of fast-substrate-rotation GLAD of HNPs made of low-cost metals (such as Cu, denoted as chiral host) and galvanic replacement of chiral hosts with noble metals (such as Ag, Au, Pt, and so on). Limit, controllable usage of noble metal salts in the galvanic replacement reaction not only reduces the production cost of noble metals, but also leads to generating alloy HNPs with tunable alloy composition. Systematic characterizations of nanostructure, material and optical activity are operated to study the galvanic replacement processes and dynamics. This work paves the way to generating novel asymmetric catalysts to operate heterogeneous asymmetric catalysis with high enantioselectivity, and to dramatically enhancing enantiodifferentiation by amplifying optical activity of enantiomers.

Photocatalytic Supramolecular Enantiodifferentiating Dimerization of 2-Anthracenecarboxylic Acid through Triplet-Triplet Annihilation.

Visible-light-driven enantiodifferentiating photodimerization of 2-anthracenecarboxylic acid (AC) sensitized by Schiff base Pt(II) complex-grafted γ-cyclodextrins leads the first triplet-triplet annihilation-based catalytic photochirogenesis. The syn-head-to-tail (HT) photodimer 2 was achieved in up to 31.4% ee at 61.0% conversion in the presence of 0.5% equiv of the photocatalyst.

Light Harvesting and Direct Electron Injection by Interfacial Charge-Transfer Transitions between TiO2 and Carboxy-Anchor Dye LEG4 in Dye-Sensitized Solar Cells

Dye-sensitized solar cells (DSSC) have attracted much attention as a promising candidate for next-generation solar cells. Recently, the solar-to-electrical energy conversion efficiency of DSSC was improved up to ca. 14%. Nevertheless, further improvement of the solar energy conversion is required for practical applications of DSSC. The performance of DSSC is limited by energy loss larger than ca. 0.3 eV in the electron injection from photoexcited dyes to TiO2. Interfacial charge-transfer transitions (ICT) between TiO2 and dyes provide a direct electron-injection mechanism with internal quantum efficiency of 100% and without energy loss. Recently, we demonstrated efficient photoelectric conversion due to ICT transitions between TiO2 nanoparticles and 2-anthracenecarboxylic acid. In this paper, we report that ICT transitions between TiO2 nanoparticles and a donor–acceptor organic dye called LEG4 bearing a carboxy anchor group extend the spectral sensitivity of the LEG4-based DSSC to the near IR region. Our ...

Switched enantioselectivity by solvent components and temperature in photocyclodimerization of 2-anthracenecarboxylate with 6A,6X-diguanidio−γ-cyclodextrins

A series of 6A,6X-diguanidio-γ-cyclodextrins (CDs) were used as chiral hosts for mediating the enantiodifferentiating [4+4] photocyclodimerization of 2-anthracenecarboxylic acid (AC). These γ-CD derivatives form stable 1:2 ternary complexes with AC in aqueous ammonia solutions and the head-to-head photodimers 3 and 4 were greatly enhanced in the presence of these diguanidio-γ-CDs. The enantioselectivity of chiral photodimers 2 and 3 is a critical function of the temperature and the ammonia contents, showing inverted product chirality by changing these external factors.

Regioselective Molecularly Imprinted Reaction Field for [4 + 4] Photocyclodimerization of 2-Anthracenecarboxylic Acid.

Molecularly imprinted cavities have functioned as a regioselective reaction field for the [4 + 4] photocyclodimerization of 2-anthracenecarboxylic acid (2-AC). Molecularly imprinted polymers were prepared by precipitation polymerization of N-methacryloyl-4-aminobenzamidine as a functional monomer to form a complex with template 2-AC and ethylene glycol dimethacrylate as a crosslinking monomer. The 2-AC-imprinted cavities thus constructed preferentially bound 2-AC with an affinity greater than that toward structurally related 9-anthracenecarboxylic acid, 2-aminoanthracene, and unsubstituted anthracene. Moreover, from the four possible regioisomeric cyclodimers, they mediated the [4 + 4] photocyclodimerization of 2-AC specifically to the anti-head-to-tail (anti-HT) isomer. This indicates that the imprinted cavities accommodate two 2-AC molecules in an anti-HT manner, thereby facilitating the subsequent regioselective photocyclodimerization.

Resonances of the anthracenyl anion probed by frequency-resolved photoelectron imaging of collision-induced dissociated anthracene carboxylic acid.

Resonances in polyaromatic hydrocarbon (PAH) anions are key intermediates in a number of processes such as electron transfer in organic electronics and electron attachment in the interstellar medium. Here we present a frequency- and angle-resolved photoelectron imaging study of the 9-anthracenyl anion generated through collision induced dissociation (CID) of its electrosprayed deprotonated anthracene carboxylic acid anion. We show that a number of π* resonances are active in the first 2.5 eV above the threshold. The photoelectron spectra and angular distributions revealed that nuclear dynamics compete with autodetachment for one of the resonances, while higher-lying resonances were dominated by prompt autodetachment. Based on electronic structure calculations, these observations were accounted for on the basis of the expected autodetachment rates of the resonances. Virtually no ground state recovery was observed, suggesting that the smallest deprotonated PAH that leads to ground state recovery is the tetracenyl anion, for which clear thermionic emission has been observed. The use of CID and photodissociation of organic carboxylic acid anions is discussed as a route to studying the dynamics of resonances in larger PAH anions.

A Star-shaped Oligo(phenylenevinylene) Liquid Crystal Host with an Anthracene Guest-A Double Nanosegregating Supermesogen.

Hexasubstituted C3 -symmetric benzenes with three elongated shape-persistent oligo(phenylenevinylene) arms and three pyridyl hydrogen-bond acceptors have been synthesized. These mesogens assemble in a double-helical columnar liquid crystal (LC) structure, owing to the compensation of free spaces between conjugated arms by dimer formation. The void is filled also by up to three anthracene carboxylic acids as guests forming hydrogen bonded supermesogens assembling in columnar LC and soft-crystal phases. Thin film fluorescence and solid-state NMR spectroscopy imply a transition from a disordered columnar LC to an unexpected double nanosegregated morphology of a filled soft columnar crystal phase. An additional intracolumnar separation of anthracene and oligo(phenylenevinylene) chromophores occurs, separate to the general segregation of aliphatic and aromatic building blocks in LC structures. The new type of supermesogens will enable the rational design of host-guest double cables with a wide range of different conjugated building blocks.

Supramolecular Photochirogenesis with a Higher-Order Complex: Highly Accelerated Exclusively Head-to-Head Photocyclodimerization of 2-Anthracenecarboxylic Acid via 2:2 Complexation with Prolinol.

An unprecedented 2:2 complex was shown to intervene in the enantiodifferentiating photocyclodimerization of 2-anthracenecarboxylic acid (A) mediated by a hydrogen-bonding template l-prolinol (P) to accelerate the formation of chiral anti-head-to-head and achiral syn-head-to-head cyclodimers in >99% combined yield with enhanced enantioselectivities of up to 72% ee for the former. The supramolecular complexation and photochirogenic behaviors, as well as the plausible structures, of intervening Am·Pn complexes (m, n = 1 or 2) were elucidated by combined theoretical and experimental spectroscopic, photophysical, and photochemical studies. Furthermore, the photochemical chiral amplification was achieved for the first time by utilizing the preferential 2:2 complexation of A with homochiral P to give normalized product enantioselectivities higher than those of the template used. The present strategy based on the higher-order hydrogen-bonding motif, which is potentially applicable to a variety of carboxylic acids and β-aminoalcohols, is not only conceptually new and expandable to other (photo)chirogenic and sensing systems but also may serve as a versatile tool for achieving photochemical asymmetric amplification and constructing chiral functional supramolecular architectures.