Myroslav O. Vysotsky

Noncovalent Assembly of [2]Rotaxane Architectures

Reversible zinc-pyridine coordination and hydrogen-bonding interactions have been used to assemble a [2]rotaxane from three components. Cooperativity in the macrocyclization process that results in the porphyrin dimer makes the system exceptionally stable. However, the kinetic lability of the zinc-porphyrin interaction means the dimer is in dynamic equilibrium with its monomer, and this has been exploited in the construction of a [2]rotaxane.

Topologically novel multiple rotaxanes and catenanes based on tetraurea calix[4]arenes

Calix[4]arenes bearing at their wide rim four urea residues easily form hydrogen bonded dimeric capsules. This has been used to preorganise alkenyl functions attached to these urea groups for their controlled connection via metathesis reaction. Multimacrocyclic tetraurea derivatives are thus obtained in excellent yields via heterodimers which are formed exclusively with tetratosylurea derivatives. Heterodimerisation of such bis- and tetraloop tetraureas leads analogously to multicatenanes, or to rotaxanes by stoppering. Huge macrocycles are detached from tetraloop derivatives by cleavage of the urea function.

OH–π and halogen–π interactions as driving forces in the crystal organisations of tri-bromo and tri-iodo trityl alcohols

The trityl alcohols bearing three bromine or three iodine atoms at the para-positions of the aromatic units, have been known for more than a hundred years. In our case these compounds have been synthesized in one-pot sequence starting from the 1,4-dihalogenobenzenes via mono-lithiation and the successive reaction with diethylcarbonate. The compounds have been crystallized from different solvent mixtures leading to one structure of bromo- (A) and three structures of iodo trityl alcohols (B–D). The inclusion of dichloromethane (C) or benzene (D) in the crystalline lattices has been observed. In all cases the OH–π and halogen–π (and in one case the halogen-halogen and CH-O weak) contacts play crucial role in the crystal organisation. The common motif of the packing is the anti parallel arrangement of the trityl alcohol molecules into infinite chains. There is the gradual change in the intermolecular interactions going from the structures A and B, where only OH–π contacts between anti-parallel molecules are observed, to C with OH–π bifurcated contacts between anti-parallel molecules and further to the structure D, where practically no OH–π contacts are observed any longer. However in the case of D the splitting of the chain with anti-parallel molecules into two anti-parallel chains with parallelly assembled molecules takes place. These OH–π chains interact further with each other either via halogen–π or/and halogen–halogen, CH–O weak interactions. The shortest contacts found are 3.429 A (1/A, Br–π) and 3.486 A (2/D, I–π) while the longest contacts are 3.558 A (1/A, Br–π) and 3.668 A (2/B, I–π). No short contacts between the included solvent molecules and triiodo trityl alcohol within the structures C and D, have been observed. The quantum chemical calculations (DFT on the M05-2X/6-311G(d,p) level) gave the following interaction energies (kcal mol−1) between two neighbouring molecules of one “OH–π chain”: −7.96 (A), −6.60 (B), −6.43 (C) and −6.45 (D), while the interaction energies via the halogen–π contacts vary from −2.17 to −3.58 kcal mol−1 (per one contact).

Gas sensing properties of porphyrin assemblies prepared using ultra-fast LB deposition

The UV–vis absorbance spectrum of LB film assemblies of 5,10,15,20-tetrakis(3,4-bis[2-ethylhexyloxyphenyl])-21H,23H-porphine is very sensitive to low concentrations of NO2. LB films prepared at very high deposition rates (∼1000 mm min−1) yield t50 response and recovery times of 25 and 33 s, respectively, and show a sensitivity of 60% relative absorbance change (at 430 nm) for 4.4 ppm NO2. Atomic force microscopy shows that the morphology of these films is characterised by isolated micron-size domains, which are themselves composed of grains of several nm in diameter. This unconventional LB structure leads to a useful sensing material as a result of the molecular functionality of the porphyrin coupled to the enhanced surface area of the porous film assembly. The optical response of the EHO gradually decreases as its temperature is increased, resulting from the shift in the adsorption-desorption equilibrium towards desorption. An activation energy for adsorption of 0.68 eV is obtained. The spectrum recovers fully after exposure to NO2 and the rate of recovery can be accelerated dramatically with gentle heating (∼350 K) for a few seconds. The concentration dependence of the optical response over the range 0.8–4.4 ppm follows a Langmuir model.

Surface plasmon resonance properties and gas response in porphyrin Langmuir–Blodgett films

Abstract Surface plasmon resonance (SPR) properties were measured for porphyrin Langmuir–Blodgett (LB) films and the response to NO 2 gas was investigated. The porphyrin molecule was 5,10,15,20-tetrakis(3,4-bis[2-ethylhexyloxyphenyl])-21H,23H-porphine (EHO). The EHO porphyrin LB films were deposited onto the cover glass with evaporated Ag thin films by vertical dipping method with a very fast deposition rate of 1000 mm min −1 . The SPR measurements were carried out at wavelengths of 488 and 632.8 nm. The SPR properties measured at 488 nm were considered to be related to the dispersion properties due to the optical absorption band of the EHO LB films. The thickness and the complex dielectric constants of the EHO LB films evaluated from the SPR properties measured at 632.8 nm were thought to be related to the island structure of the EHO LB films. From the NO 2 gas response measurements, the SPR properties at 488 nm were found to be more sensitive to NO 2 gas than those at 632.8 nm. The response rate to NO 2 gas and the recovery properties were also examined.

Compensation of steric demand by cation–π interactions, cobaltocenium cations as guests in tetraurea calix[4]arene dimers

The affinities of ferrocene (2) and the cobaltocenium cation (3+), which have roughly the same size and differ in their charge, towards the inner cavity of the dimeric capsule formed by tetraurea calix[4]arene (1) were studied in C2D4Cl2 solutions. While 3+, which occupies more than 75% of the internal volume of the dimer, is readily encapsulated this is not the case for 2. This is probably due to cation-pi interactions, which operate only between 3+ and the aromatic rings of the calix[4]arene dimer. We found that the affinity of the cobaltocenium cation is higher than that of the tropylium cation (4+) and is only 2-3 times less than that of the tetraethylammoniun cation (5+). From the variable temperature 1H NMR spectra of this capsule, the free energy of activation at 298 K (deltaGdouble dagger(298K)) for the reorientation of the hydrogen bonded belt between the two parts of the dimer could be determined by total line shape analysis for the aromatic protons of the calixarene. The value of 14.3 +/- 0.2 kcal mol(-1) for the dimeric capsules of 3+ PF6- is very similar to the free activation energy found for dimeric capsules of 1 with 4+ PF6- and 5+ PF6- in C2D4Cl2. It becomes significantly lower, if PF6- is replaced by BF4-. We also found that ten times more DMSO is needed to disrupt the capsule 1 x 3+ x 1 than the corresponding 1 x 1 dimer containing benzene as guest. This demonstrates again the importance of the cation-pi interactions for the stability of such hydrogen-bonded dimeric capsules.

Columnar supramolecular architecture of crystals of 2-(4-Iodophenyl)-1,10-phenanthroline derived from values of intermolecular interaction energy

Using results of X-ray diffraction study supramolecular architecture of crystals of 2-(4-iodophenyl)-1,10-phenanthroline has been analyzed on the basis of quantum-chemical calculations of intermolecular interactions energy. It is demonstrated that these crystals have three levels of organization. Molecules form stacked dimers with the highest binding energy (first level). These dimers represent basic unit of infinite columns stabilized by stacking interactions between dimers (second level). The energy of intermolecular interactions between neighbouring stacked columns is very close. This does not allow to figure out any layers in the crystal. Therefore crystals of this compound have columnar structure with almost isotropic packing of stacked columns (third level).

Dimeric capsules of tetraurea calix[4]arenes. MD simulations and X-ray structure, a comparison

The single crystal X-ray structure of a homodimer of a tetra(tolylurea) calix[4]arene including a tetraethylammonium cation as guest shows an expansion of the capsule and a distortion of its shape, in comparison to the structure of a similar dimer with an encapsulated benzene molecule. Thus, only 8 of 16 possible hydrogen bonds are present in the hydrogen bonded belt holding together the two hemispheres. The encapsulated cation is disordered over two equivalent positions with two methyl groups pointing to the equator, while two methyl groups pointing to the poles form CH–π interactions with the inner surfaces of the calixarene cavities. MD simulations are in agreement with the distorted X-ray structure for a short simulation time of 1–2 ns with a given orientation of the included cation and approach for longer simulation times (9 ns) the fourfold symmetry found by 1H NMR spectroscopy in solution.

Taking advantage of optical and electrical properties of organic molecules for gas sensing applications

Abstract The discipline of molecular electronics has grown rapidly over the last 10 years and is driven by the promise of the enhanced applied physical properties of functionalised organic materials compared to their inorganic partners. The subject can be divided generally into two broad themes, namely active molecular-scale electronics (or photonics), in which the control or generation of charge (or photons) at the nanoscale is attempted, and passive supra-molecular electronics (or photonics), in which the specific functionality of the molecules is modified by some interaction or process. In this paper, an example of the latter approach to molecular electronics will be given and this will describe the gas sensing properties of a tetra-substituted porphyrin molecule. The optical absorbance spectrum of LB film assemblies of 5,10,15,20-tetrakis(3,4-bis[2-ethylhexyloxy]phenyl)-21H,23H-porphine (EHO) is highly sensitive to low concentrations of NO 2 . LB films prepared at much faster than conventional deposition rates (∼1000 mm min −1 ) yield t 50 response and recovery times of 25 and 33 s, respectively, and show a sensitivity of 60% relative absorbance change (at 430 nm) for 4.4 ppm NO 2 . The morphology of these films is revealed using atomic force microscopy to contain isolated micron-size domains which are composed of grains of several nm in diameter. This unconventional structure leads to a useful sensing material as a result of the molecular functionality of the porphyrin coupled to the enhanced surface area of the porous film assembly. The EHO film shows a gradually diminishing optical response as its temperature is increased, resulting from the shift in the adsorption–desorption equilibrium towards desorption. The spectrum recovers fully after exposure to NO 2 . The rate of recovery is slow at room temperature but can be accelerated dramatically with gentle heating (∼350 K) for a few seconds. The kinetics of the gas sensing process have been modelled and found to fit Elovichian surface adsorption for an initial fast surface adsorption process. This is followed by a much slower diffusive process in which the NO 2 molecules diffuse through the bulk of the assembly. The concentration dependence of the optical response over the range 0.8–4.4 ppm follows a Langmuir model.

Inherently chiral calix[4]arenes with asymmetrical superposition of substituents at the lower and the upper rims of macrocycle

Abstract Three types of inherently chiral calix[4]arenes( AAHH BHBH , AHHH HBBH , AAHH HHBH ) with asymmetrical superposition of ethyl, diethoxyphosphoryl groups at the lower rim of the macrocycle and bromine atoms at the upper rim, have been synthesized. The key steps of the synthesis are O,O′-phosphorotropic rearrangements of 1,3-distally disubstituted calix[4]arenes into 1,2-proximal isomers, regioselective bromination of the upper rim and hydrolytic removing of phosphoryl or benzoyl group from the lower rim.