The effect of a heteroatom on the structure and vibrational spectra of Heteroannulated tetraphenylenes

Based on calculations by the DFT method, we have theoretically compared IR absorption and Raman spectra of tetraoxa[8]circulene (4O) and its analogs that contain sulfur (4S) and selenium (4Se) atoms. Calculations have shown that the structure of investigated molecules and observed shifts of similar vibrations in their IR and Raman spectra are interrelated. We have constructed correlation schemes of frequency shifts of normal vibrations upon passage from planar 4O circulene to its 4S and 4Se nonplanar analogs. The obtained data are of fundamental interest both from the point of view of specific selection rules and in the context of the novelty of the force field, where the conjugation of the internal and external macrocycles with heteroatoms manifests itself

Temperature effects in low-frequency Raman spectra of corticosteroid hormones

Experimental Raman spectra of the corticosteroid hormones corticosterone and desoxycorticosterone are recorded at different temperatures (in the range of 30–310 K) in the region of low-frequency (15–120 cm−1) vibrations using a solid-state laser at 532.1 nm. The intramolecular vibrations of both hormones are interpreted on the basis of Raman spectra calculated by the B3LYP/6-31G(d) density functional theory method. The intermolecular bonds in tetramers of hormones are studied with the help of the topological theory of Bader using data of X-ray structural analysis for crystalline samples of hormones. The total energy of intermolecular interactions in the tetramer of desoxycorticosterone (−49.1 kJ/mol) is higher than in the tetramer of corticosterone (−36.9 kJ/mol). A strong intramolecular hydrogen bond O21-H⋯O=C20 with an energy of −42.4 kJ/mol was revealed in the corticosterone molecule, which is absent in the desoxycorticosterone molecule. This fact makes the Raman spectra of both hormones somewhat different. It is shown that the low-frequency lines in the Raman spectra are associated with skeletal vibrations of molecules and bending vibrations of the substituent at the C17 atom. The calculated Raman spectrum of the desoxycorticosterone dimer allows one to explain the splitting and shift of some lines and to interpret new strong lines observed in the spectra at low temperatures, which are caused by the intermolecular interaction and mixing of normal vibrations in a crystal cell. On the whole the calculated frequencies are in a good agreement with the experimental results

Electronic structure, aromaticity and spectra of hetero[8]circulenes

The present review highlights recent advances in experimental and theoretical chemistry dealing with investigation of the electronic structures and physicochemical properties of hetero[8]circulenes. These compounds are the only representatives of planar heteroannulated cyclooctatetraenes. It is shown that high molecular symmetry of hetero[8]circulenes and the extended specific π-conjugated chain are the main factors responsible for high stability of the crystal packing modes and the optical and magnetic properties of these compounds. These effects also determine numerous selection rules for electronic and vibrational transitions in UV-Vis, IR and Raman spectra. Emphasis is given to the aromaticity of hetero[8]circulenes containing the inner antiaromatic cyclooctatetraene core. The planar structure of the latter is stabilized by a polyaromatic system composed of benzene rings and five-membered heterocycles. Due to high thermal and chemical stability of most hetero[8]circulenes combined with semiconducting properties, these compounds can be considered as promising materials for molecular electronics and nanophotonics, in particular for the production of organic light-emitting diodes and field-effect transistors

Electronic structure, aromaticity and spectra of hetero[8]circulenes

The present review highlights recent advances in experimental and theoretical chemistry dealing with investigation of the electronic structures and physicochemical properties of hetero[8]circulenes. These compounds are the only representatives of planar heteroannulated cyclooctatetraenes. It is shown that high molecular symmetry of hetero[8]circulenes and the extended specific π-conjugated chain are the main factors responsible for high stability of the crystal packing modes and the optical and magnetic properties of these compounds. These effects also determine numerous selection rules for electronic and vibrational transitions in UV-Vis, IR and Raman spectra. Emphasis is given to the aromaticity of hetero[8]circulenes containing the inner antiaromatic cyclooctatetraene core. The planar structure of the latter is stabilized by a polyaromatic system composed of benzene rings and five-membered heterocycles. Due to high thermal and chemical stability of most hetero[8]circulenes combined with semiconducting properties, these compounds can be considered as promising materials for molecular electronics and nanophotonics, in particular for the production of organic light-emitting diodes and field-effect transistors

The effect of a heteroatom on the structure and vibrational spectra of Heteroannulated tetraphenylenes

Based on calculations by the DFT method, we have theoretically compared IR absorption and Raman spectra of tetraoxa[8]circulene (4O) and its analogs that contain sulfur (4S) and selenium (4Se) atoms. Calculations have shown that the structure of investigated molecules and observed shifts of similar vibrations in their IR and Raman spectra are interrelated. We have constructed correlation schemes of frequency shifts of normal vibrations upon passage from planar 4O circulene to its 4S and 4Se nonplanar analogs. The obtained data are of fundamental interest both from the point of view of specific selection rules and in the context of the novelty of the force field, where the conjugation of the internal and external macrocycles with heteroatoms manifests itself

Recent progress in quantum chemistry of hetero[8]circulenes

This mini-review presents recent advances in theory of electronic and spectral properties of hetero[8]circulenes used as promising fluorescent emitters for organic light-emitting diodes. Special attention is paid to the possibility of their further functionalisation into one-dimensional and two-dimensional (2D) materials. Such materials are predicted to be useful ambipolar organic semiconductors showing high charge carrier mobility. The porous structure of hetero[8]circulene-based nano-arrays can also provide suitable hydrogen storage materials, biomimetic-type nanopores and ionic channels. They serve as a good example of the density functional theory application for design of stable 2D structures, which extends the family of graphene-like materials