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

Ab Initio Study of Phosphorescence of Hetero[8]circulenes

Peer reviewe

Single-layer polymeric tetraoxa[8]circulene modified by s-block metals : toward stable spin qubits and novel superconductors

Tunable electronic properties of low-dimensional materials have been the object of extensive research, as such properties are highly desirable in order to provide flexibility in the design and optimization of functional devices. In this study, we account for the fact that such properties can be tuned by embedding diverse metal atoms and theoretically study a series of new organometallic porous sheets based on two-dimensional tetraoxa[8]circulene (TOC) polymers doped with alkali or alkaline-earth metals. The results reveal that the metal-decorated sheets change their electronic structure from semiconducting to metallic behaviour due to n-doping. Complete active space self-consistent field (CASSCF) calculations reveal a unique open-shell singlet ground state in the TOC-Ca complex, which is formed by two closed-shell species. Moreover, Ca becomes a doublet state, which is promising for magnetic quantum bit applications due to the long spin coherence time. Ca-doped TOC also demonstrates a high density of states in the vicinity of the Fermi level and induced superconductivity. Using the ab initio Eliashberg formalism, we find that the TOC-Ca polymers are phonon-mediated superconductors with a critical temperature T-C = 14.5 K, which is within the range of typical carbon based superconducting materials. Therefore, combining the proved superconductivity and the long spin lifetime in doublet Ca, such materials could be an ideal platform for the realization of quantum bits.Peer reviewe

Aromaticity of the doubly charged [8]circulenes

Magnetically induced current densities and current pathways have been calculated for a series of fully annelated dicationic and dianionic tetraphenylenes, which are also named [8]circulenes. The gauge including magnetically induced current (GIMIC) method has been employed for calculating the current density susceptibilities. The aromatic character and current pathways are deduced from the calculated current density susceptibilities showing that the neutral [8]circulenes have two concentric pathways with aromatic and antiaromatic character, respectively. The inner octatetraene core (the hub) is found to sustain a paratropic (antiaromatic) ring current, whereas the ring current along the outer part of the macrocycle (the rim) is diatropic (aromatic). The neutral [8]circulenes can be considered nonaromatic, because the sum of the ring-current strengths of the hub and the rim almost vanishes. The aromatic character of the doubly charged [8]circulenes is completely different: the dianionic [8]circulenes and the OC-, CH-, CH2-, SiH-, GeH-, SiH2-, and GeH2-containing dicationic species sustain net diatropic ring currents i.e., they are aromatic, whereas the O-, S-, Se-, NH-, PH- and AsH-containing dicationic [8]circulenes are strongly antiaromatic. The present study also shows that GIMIC calculations on the [8]circulenes provide more accurate information about the aromatic character than that obtained using local indices such as nuclear-independent chemical shifts (NICSs) and H-1 NMR chemical shifts.Peer reviewe

A hybrid molecular sensitizer for triplet fusion upconversion

Triplet fusion upconversion is useful for a broad spectrum of applications ranging from solar cells, photoredox catalysis, to biophotonics applications, especially in the near-infrared (NIR,>700 nm) range. This upconverting system typically demands efficient conversion of spin-singlet harvested energy through intersystem crossing to spin-triplet states, accessible only in rare metallic-coordinating macrocycle compounds or heavy-metal-containing semiconductor quantum dots for triplet sensitization. Herein, we describe an organic–inorganic system for NIR-to-visible triplet fusion upconversion, interfacing commonly-seen, non-metallic, infrared dyes (IR806, IR780, indyocynine green, and CarCl) and lanthanide nanocrystal (sodium ytterbium fluoride) as a hybrid molecular sensitizer, which extracts molecular spin-singlet energy to nanocrystal-enriched ytterbium dopants at ~48% efficiency (IR806, photoexciation at 808 nm). Moreover, ytterbium sub-lattice energy migration increases the interaction possibility between the nanocrystal and the freely-diffusing rubrenes in solution, resulting in 24-fold (IR806) to 1740-fold (indocyanine green) upconversion (600 nm) increase, depending on the IR dye type, as compared to the one without ytterbium nanotransducers. Ab initio quantum chemistry calculations identify enhanced spin-orbital coupling in the ytterbium-IR806 complex and high energy transfer rate in the ytterbium-rubrene interaction (1010 s 1). Employing inorganic lanthanide nanocrystals as nanotransducers unleashes the potential use of non-metallic infrared organic dyes for triplet fusion upconversion

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

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

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