A theoretical study on the conformations and energetics on the cation–π interaction between monovalent ions (M+=Li+, Na+, and K+) and anthracene and phenanthrene molecules

Polyether-Based Diblock Terpolymer Micelles with Pendant Anthracene Units-Light-Induced Crosslinking and Limitations Regarding Reversibility

The synthesis of 9-methylanthracenyl glycidyl ether (AnthGE) as a crosslinkable monomer that can be applied in anionic ring opening polymerization is reported. Diblock terpolymers of the composition methoxy-poly(ethylene oxide)-block-poly(2-ethylhexyl glycidyl ether-co-9-methylanthracenyl glycidyl ether) (mPEO-b-P(EHGE-co-AnthGE) with 10 to 24 wt% of AnthGE are synthesized and characterized. Their micellization behavior, as well as their light-induced core-crosslinking via irradiation with UV light (λ = 365 nm) is studied. The results are compared with studies on the dimerization, and the dimer cleavage via irradiation with UV-C light (λ = 254 nm), of the same diblock terpolymer in organic solution, and the small-molecule model compound 9-methoxymethylanthracene. Differences in ¹ H NMR spectra of the crosslinked or dimerized compounds and reaction kinetics of the dimerization reactions under different conditions suggest possible side reactions for the case of the core-crosslinking of micelles in aqueous solution. These side reactions limit the reversibility of the anthracene dimerization reaction in aqueous solutions, even if the anthracene molecule is encapsulated within the hydrophobic core of a polymeric micelle.

Electrochemical determination of phenanthrene based on anthraquinone sulfonate and poly diallyldimethylammonium chloride modified indium–tin oxide electrode

The amount of Phe could be quantified by the electrochemical oxidation peak current difference of AQS at AQS/PDDA/ITO through the specific interaction between AQS and Phe.

Controlling the doping level of double-walled carbon nanotubes by using aromatic hydrocarbon complexes

The level of potassium doping in double-walled carbon nanotubes has been tailored by the combination of potassium and aromatic hydrocarbons in a polar solvent.

Organometallic Polymers Assembled from Cation–π Interactions: Use of Ferrocene as a Ditopic Linker Within the Homologous Series [{(Me3Si)2NM}2⋅(Cp2Fe)]∞ (M=Na, K, Rb, Cs; Cp=cyclopentadienyl)

Addition of ferrocene to solutions of alkali metal hexamethyldisilazides M(HMDS) in arenes (in which M=Na, K, Rb, Cs) allows the subsequent crystallization of the homologous series of compounds [{(Me(3)Si)(2)NM}(2) (Cp(2)Fe)](infinity) (1-4). Similar reactions using LiHMDS led to the recrystallization of the starting materials. The crystal structures of 1-4 reveal the formation of one-dimensional chains composed of dimeric [{M(HMDS)}(2)] aggregates, which are bridged through neutral ferrocene molecules by eta(5)-cation-pi interactions. In addition, compounds 3 and 4 also contain interchain agostic M--C interactions, producing two-dimensional 4(4)-nets. Whereas 1 and 2 were prepared from toluene, the syntheses of 3 and 4 required the use of tert-butylbenzene as the reaction media. The attempted crystallization of 3 and 4 from toluene resulted in formation of the mixed toluene/ferrocene solvated complexes [{(Me(3)Si)(2)NM)(2)}(2) (Cp(2)Fe)(x)(Tol)(y)](infinity) (in which M=Rb, x=0.6, y=0.8, 5; M=Cs, x=0.5, y=1, 6). The extended solid-state structures of 5 and 6 are closely related to the 4(4)-sheets 3 and 4, but are now assembled from a combination of cation-pi, agostic, and pi-pi interactions. The charge-separated complex [K{(C(6)H(6))(2)Cr}(1.5)(Mes)][Mg(HMDS)(3)] (15) was also structurally characterized and found to adopt an anionic two-dimensional 6(3)-network through doubly eta(3)-coordinated bis(benzene)chromium molecules. DFT calculations at the B3 LYP/6-31G* level of theory indicate that the binding energies of both ferrocene and toluene to the M(HMDS) dimers increases in the sequence Li<Na<K. This pattern is a consequence of the larger metals allowing more open coordination spheres to support cation-pi contacts. By comparison, binding of the isolated metal cations to the aromatic groups follow the reverse order K<Na<Li. A combined analysis of theoretical and experimental data suggest that ferrocene is a stronger cation-pi donor than toluene for the lighter metals, but that this difference is eliminated on descending the group.

Resolution of ultrafast pyrene excimer emission rise times in zeolites X and Y

Pyrene has been a favorite photophysical probe molecule for zeolite research because of its ability to exhibit both monomer and excimer emission upon excitation. This study combines the use of ultrafast time-resolved fluorescence spectroscopy with steady-state fluorescence spectroscopy to study the excimer emission of pyrene incorporated within zeolites LiY, NaY, KY and NaX. The effects of sealing technique and coincorporated solvents are also explored. Pyrene excimer emission is resolvable with the use of an ultrafast streak camera under all conditions examined in this study with a rise-time range of 6.8 to 16.0 picoseconds. For each zeolite sample the addition of cosolvents decreases the rise time, with a greater decrease for polar solvents than for a nonpolar solvent. The presence of a detectable rise time for excimer emission indicates that pyrene excimer formation is a dynamic process when pyrene is embedded within the cavities of zeolite host materials.

Application of time- and space-resolved fluorescence spectroscopy to the distribution of guest species into micrometer-sized zeolite crystals

We measured the fluorescence decays and spectra of perylene adsorbed from solution into zeolite X crystals of 2-3 microm in diameter at the level of individual crystals by the application of a microscopy method coupled with a single photon counting apparatus and a multichannel spectrophotometer. We found that both decays and spectra are particle-dependent, i.e. a particle-to-particle difference was observed for the fluorescence decay curves at a fixed loading level along with a particle-dependent spectral change due to the various contribution of excimer emission band relative to those of three monomers. These findings are due to a non-homogeneous distribution which is confirmed by the various emission intensities of perylene-loaded zeolite crystals observed by fluorescence microscopy. Previously, a homogeneous distribution of the guest between zeolite crystals has been just taken for granted and not justified by experiment. The present result suggests that commonly employed collective measurements such as UV-VIS absorption and emission spectroscopies, IR and Raman spectroscopies, and NMR of bulk zeolite powders provide only averaged results and may sometimes suffer from acquiring precise molecular level pictures.

Cation [M = H+, Li+, Na+, K+, Ca2+, Mg2+, NH4+, and NMe4+] Interactions with the Aromatic Motifs of Naturally Occurring Amino Acids: A Theoretical Study

Ab initio (HF, MP2, and CCSD(T)) and DFT (B3LYP) calculations were done in modeling the cation (H(+), Li(+), Na(+), K(+), Ca(2+), Mg(2+), NH(4)(+), and NMe(4)(+)) interaction with aromatic side chain motifs of four amino acids (viz., phenylalanine, tyrosine, tryptophan and histidine). As the metal ion approaches the pi-framework of the model systems, they form strongly bound cation-pi complexes, where the metal ion is symmetrically disposed with respect to all ring atoms. In contrast, proton prefers to bind covalently to one of the ring carbons. The NH(4)(+) and NMe(4)(+) ions have shown N-H...pi interaction and C-H...pi interaction with the aromatic motifs. The interaction energies of N-H...pi and C-H...pi complexes are higher than hydrogen bonding interactions; thus, the orientation of aromatic side chains in protein is effected in the presence of ammonium ions. However, the regioselectivity of metal ion complexation is controlled by the affinity of the site of attack. In the imidazole unit of histidine the ring nitrogen has much higher metal ion (as well as proton) affinity as compared to the pi-face, facilitating the in-plane complexation of the metal ions. The interaction energies increase in the order of 1-M < 2-M < 3-M < 4-M < 5-M for all the metal ion considered. Similarly, the complexation energies with the model systems decrease in the following order: Mg(2+) > Ca(2+) > Li(+) > Na(+) > K(+) congruent with NH(4)(+) > NMe(4)(+). The variation of the bond lengths and the extent of charge transfer upon complexation correlate well with the computed interaction energies.

Molecular structures of cation...pi(arene) interactions for alkali metals with pi- and sigma-modalities

The monovalent cations of Na(+), K(+), Rb(+), and Cs(+) derived from the highly electropositive alkali metals represent prototypical charged spheres that are mainly subject to relatively simple electrostatic and solvation (hydration) forces. We now find that the largest of these Rb(+) and Cs(+) are involved in rather strong cation...pi(arene) interactions when they are suitably disposed with the ambifunctional hexasubstituted benzene C(6)E(6). The ether tentacles (E = methoxymethyl) allow these cations to effect eta(1)-bonding to the benzene center in a manner strongly reminiscent of the classical sigma-arene complexes with positively charged electrophiles where Z(+) = CH(3)(+), Br(+), Cl(+), Et(3)Si(+), etc. The somewhat smaller potassium cation is involved in a similar M(+)...pi(arene) interaction that leads to eta(2)-bonding with the aromatic center in the pi-mode previously defined in the well-known series of silver(I)/arene complexes. We can find no evidence for significant Na(+)... pi(arene) interaction under essentially the same conditions. As such, the sigma-structure of the Rb(+) and Cs(+) complexes and pi-structure of the K(+) complex are completely integrated into the continuum of sigma-pi bondings of various types of electrophilic (cationic) acceptors with arene donors that were initially identified by Mulliken as charge-transfer.