V. B. Nazarov

Synthesis, photochromic behaviour and light-controlled complexation of 3,3-diphenyl-3H-benzo[f]chromenes containing a dimethylamino group or an aza-15-crown-5 ether unit

Synthesis of 3,3-diphenyl-3H-benzo[f]chromenes containing an aza-15-crown-5-ether unit or a dimethylamino group and spectrokinetic study of light-controlled complexation of these compounds with Ca2+ in acetonitrile are reported. The affinity of the azacrown chromene to Ca2+ decreases substantially upon a photoinduced ring-opening reaction. In contrast, dimethylamino chromene, which is unable to bind Ca2+ in the dark, shows a low cation-binding capacity upon UV irradiation. The spectroscopic and kinetic behaviour of the photomerocyanine isomers of these chromenes is strongly affected by complexation with Ca2+. A semi-empirical quantum-chemical study of the merocyanine isomers was applied to interpret the experimental data.

Long-lived room temperature phosphorescence of a naphthalene-β-cyclodextrin-adamantane complex in the presence of oxygen

Naphthalene-d8—β-cyclodextrin—adamantane triple complexes were prepared in an aqueous solution at room temperature. Irradiation (λ = 285 nm) of the solution in the presence of molecular oxygen results in the long-lived (τ = 10.3 s) room temperature phosphorescence (RTP). The removal of oxygen from the solution increases the RTP intensity and phosphorescence lifetime by 1.5 times. The RTP spectrum contains a well-resolved vibrational structure, whose bands are assigned to full symmetric vibrations of naphthalene, their overtones, and the combination tones of full symmetric vibrations. The quantum-chemical calculation of the triple complex structure confirms that both naphthalene and adamantane can simultaneously be included into the β-cyclodextrin cavity and suggests that the role of the latter as the third component is the more efficient shielding of naphthalene from the oxygen effect due to both the formation of three-component complexes and their aggregation to form submicronic particles.

Structure of guest-host complexes of β-cyclodextrin with arenes: a quantum-chemical study

The structure of β-cyclodextrin (β-CD), as well as the structure and energetics of β-CD-naphthalene, β-CD-fluorene, β-CD-phenanthrene, β-CD-cyclohexane (1:1), and β-CD-naphthalene (2:2) inclusion complexes was studied by the semiempirical MNDO/PM3 method. Calculations of a β-CD-naphthalene-cyclohexane (1:1:1) complex were also performed. The minimum heat of formation was found for the symmetric β-CD conformation withC7 symmetry axis. The structure is stabilized by the ring of interunit H-bonds formed by the protons of the 2-OH groups and the O atoms of the 3′-OH groups of the glucose units. Preferableness of this orientation of interunit H-bonds was confirmed byab initio calculations of the molecule of α-(1–4)-glucobiose (maltose) in the MP2/6-31G(d,p)//6-31G(d,p) approximation. The formation of any inclusion compounds of β-CD with arenes is energetically favorable: the complexation energy varies in the range −9 to −12 kcal mol−1. Among complexes with naphthalene, that of composition 2:2 is the most energetically favorable, which is in agreement with experimental data. In this complex, β-CD exists as a dimer of the “head-to-head” type, in which both partners are linked by a system of H-bonds. The structure of the “head-to-head” dimer of β-CD was simulated byab initio calculations of the H-bonded dimer of α-d-glucose in the RHF/6-31G(d,p) approximation. In the dimer, both components are linked by a pair of H-bonds formed by the protons of the 3-OH groups and the O atoms of the, 2-OH groups. The dimerization energies obtained fromab initio and semiempirical MNDO/PM3 and AM1 calculations differ by about 2.5 times (8.6vs 3.2 and 3.8 kcal mol−1, respectively).

Excimer fluorescence and structures of the inclusion complexes of β-cyclodextrin with naphthalene and its derivatives

Fluorescence of the inclusion complexes with different compositions formed by naphthalene-h8, naphthalene-d8, 2,7-dimethylnaphthalene (DMN), and 2-benzylnaphthalene (BN) with β-cyclodextrin (β-CD) in water was studied. Two types of fluorescence are observed, monomer (MF) and excimer (EF_ fluorescence. The excimer fluorescence of the 2∶2 complex emitted by aggregated light-dispersing crystals forming a precipitate, whereas is the MF is concentrations, EF predominates for the resulting complexes. A proposed structure of the inclusion complexes was derived from MNDO/PM3 semiempirical quantum-chemical calculations. The EF is caused by the structure of the complex, in which both naphthalene molecules are separated by a distance of 4.7 Å: they lie in parallel orientation to each other, whereby one ring is displaced from the other by one-fourth of the length of the naphthalene ring. The complexes of 2,7-DMN and 2-benzylnaphthalene with β-CD do not exhibit EF. For the 2∶2 complex of 2,7-DMN with β-CD, this is due to the fact that the aromatic fragments are removed too far from one another 2-Benzylnaphthalene is unable to form an inclusion complex with β-CD, in whose structure the aromatic fragments inside the cavity could be arranged in parallel planes; instead, it forms a 1∶2 complex with β-CD.

Phosphorescence lifetime of naphthalene and phenanthrene in aggregated aromatic molecule-β-cyclodextrin-precipitant complexes

Aggregated aromatic molecule-β-cyclodextrin-precipitant complexes exhibit long-lived phosphorescence at room temperature in water after the chemical binding of oxygen. The temperature dependences of the phosphorescence lifetimes of naphthalene-h8, naphthalene-de, and phenanthrene in the aggregates were measured. For example, the phosphorescence lifetimes of naphthalene-d8 aggregated with β-cyclodextrin and cyclohexane are equal to 25.1, 17.6, and 6.8 s at 77, 276, and 347 K, respectively, and that of phenanthrene aggregated with isooctane and β-cyclodextrin are 3.24, 3.06, and 1.26 s at 268, 274, and 335 K, respectively. The temperature dependences of the phosphorescence lifetimes at room temperature are determined by the rate constants of the radiative and nonradiative transitions from the triplet state of an aromatic molecule.

Vibronic structure of electronic absorption and fluorescence spectra of pyrene in the complex with β-cyclodextrin in the presence of nonpolar and polar solvents

The feasibility of using pyrene as a fluorescent probe in complexes cyclodextrin-pyrene-analyte in aqueous solutions was studied for several analytes (A) of different polarity. Bands that prove the formation of the complex Py2βCD were found for the first time in the UV-VIS spectrum of an aqueous solution of pyrene in the presence of β-cyclodextrin. A characteristic of a fluorescent probe is the ratio I3/I1 in the fluorescence spectrum, where I3 is the intensity of the third vibronic line at ∼800 cm−1, and I1 is the intensity of the 0-0 transition. The value of I3/I1 for Py2βCD is highly sensitive to the addition of an analyte with a concentration of several μM/L to the aqueous solution. Dependences of (I3/I1)/C on the function of the dielectric constant ɛ of the analyte fɛ= (ɛ − 1)/(2ɛ + 1) are divided into two straight lines with different slopes for nonpolar and polar solvents. Energies of insertion of analytes into Py2βCD were calculated by the quantumchemical PM3 method. An increase in (I3/I1)/C corresponds to the more thermodynamically stable complex 2APy2βCD.

Photoluminescent organic recording media

A review on the development of photoluminescent organic recording media is presented. Particular emphasis has been placed on positive photoluminescent materials for irreversible and reversible recording of optical information. The results of the study of light-sensitive systems based on irreversible and reversible photochemical transformations or organic molecules are discussed. The fundamental characteristics for made photoluminescent polymeric materials based on these photochemical systems and perspectives of their application as recording media, especially in the modern photography and 3D- optical memory devices, are given adequate consideration.

Inclusion complexes naphthalene-γ-cyclodextrin-adamantane and naphthalene-γ-cyclodextrin-o-carborane: the structure and luminescence properties

The luminescence properties of inclusion complexes of naphthalene-d8 with γ-cyclodextrin (γ-CD) in the presence of adamantane or o-carborane added as third parties were studied in aqueous solutions. It was found that the structure of the cage compound added to the aqueous solution of the naphthalene-d8@γ-CD complex completely determines the luminescence type of the ternary complex. For instance, the intensity of excimer fluorescence (EF) band increases considerably at the expense of reduction of the intensity of monomer fluorescence (MF) band on adding adamantane. On the contrary, adding o-carborane causes a decrease in the intensity of the EF band of naphthalene-d8 and simultaneous appearance of MF in addition to long-lived room-temperature phosphorescence (RTP) whose lifetime increases from 1.5 s to 9.1 s after deoxygenation of the solution. Structural differences between the complexes affecting their behavior under the action of the third parties were explained using the results of semiempirical quantum chemical calculations.

Water Cluster for the Simulation of Hydration of Organic Compounds: Applying the DFT Method

A model of a D3 symmetry nanocluster consisting of 36 water molecules is developed. This model makes it possible to perform routine simulations of the hydration of small- to medium-sized organic molecules in the cluster using the density functional method. The hydration energies obtained agree with the available experimental data on the correlation coefficient R ≈ 0.83. The application of this model is considered with the examples of the conformational equilibrium of butane and 1,2-ethylenediamine molecules in vacuo and in an aqueous phase, the proton affinity of methylamine and pyridine, stacking interaction in benzene dimer, and proton transfer in the cluster.

Phosphorescence of aromatic molecules in complexes with crystalline β-cyclodextrin at room temperature

The rate constants for the quenching by oxygen of triplet states of aromatic molecules (naphthalenes-d8 and-h8, phenanthrene) forming inclusion complexes with crystalline β-cyclodextrin in water at 290 K are equal to 900–1300 L mol−1s−1.