| 1. |
- Baryshnikov, Gleb, et al.
(author)
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Theory and Calculation of the Phosphorescence Phenomenon
- 2017
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In: Chemical Reviews. - : American Chemical Society (ACS). - 0009-2665 .- 1520-6890. ; 117:9, s. 6500-6537
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Research review (peer-reviewed)abstract
- Phosphorescence is a phenomenon of delayed luminescence that corresponds to the radiative decay of the molecular triplet state. As a general property of molecules, phosphorescence represents a cornerstone problem of chemical physics due to the spin prohibition of the underlying triplet-singlet emission and because its analysis embraces a deep knowledge of electronic molecular structure. Phosphorescence is the simplest physical process which provides an example of spin-forbidden transformation with a characteristic spin selectivity and magnetic field dependence, being the model also for more complicated chemical reactions and for spin catalysis applications. The bridging of the spin prohibition in phosphorescence is commonly analyzed by perturbation theory, which considers the intensity borrowing from spin-allowed electronic transitions. In this review, we highlight the basic theoretical principles and computational aspects for the estimation of various phosphorescence parameters, like intensity, radiative rate constant, lifetime, polarization, zero-field splitting, and spin sublevel population. Qualitative aspects of the phosphorescence phenomenon are discussed in terms of concepts like structure-activity relationships, donor-acceptor interactions, vibronic activity, and the role of spin-orbit coupling under charge-transfer perturbations. We illustrate the theory and principles of computational phosphorescence by highlighting studies of classical examples like molecular nitrogen and oxygen, benzene, naphthalene and their azaderivatives, porphyrins, as well as by reviewing current research on systems like electrophosphorescent transition metal complexes, nucleobases, and amino acids. We furthermore discuss modern studies of phosphorescence that cover topics of applied relevance, like the design of novel photofunctional materials for organic light-emitting diodes (OLEDs), photovoltaic cells, chemical sensors, and bioimaging.
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| 2. |
- Baryshnikov, Gleb V., et al.
(author)
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A computational study of aromaticity and photophysical properties of unsymmetrical azatrioxa[8]circulenes
- 2017
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In: New Journal of Chemistry. - : Royal Society of Chemistry. - 1144-0546 .- 1369-9261. ; 41:7, s. 2717-2723
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Journal article (peer-reviewed)abstract
- Owing to their potential use in organic light-emitting diodes and field-effect transistors we present a theoretical study of a series of unsymmetrical azatrioxa[8]circulenes in order to explain the impact of outer substituents and benzoannelation on photophysical constants and aromaticity of these compounds in terms of spin-orbit coupling perturbation and magnetically-induced ring currents. It is argued that the S1-Tn inter-system crossing processes constitute the main deactivation pathways for the fluorescence quenching, something that is supported by a good agreement obtained with experimental data on fluorescence quantum yields. The concept of the gauge-including magnetically induced currents has been applied in order to estimate the role of substituents and benzoannelated fragments on the aromaticity and particularly on the overall balance between the diatropic “aromatic” and paratropic “antiaromatic” current strengths. While a variation of the substituents in the outer perimeter of the studied circulenes does not provide a clear effect on their aromaticity, it is demonstrated that an additional benzoannelation (π-extension) of the azatrioxa[8]circulene macrocycle induces a significant aromaticity enhancement.
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| 3. |
- Baryshnikov, Glib V., et al.
(author)
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Anion-induced exchange interactions in binuclear complexes of Cu(II) with flexible hexadentate bispicolylamidrazone ligands
- 2016
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In: Chemical Physics Letters. - : Elsevier. - 0009-2614 .- 1873-4448. ; 661, s. 48-52
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Journal article (peer-reviewed)abstract
- Two recently synthesized copper(II) complexes with spacer-armed bispicolylamidrazone ligands have been theoretically studied at the density functional theory (DFT) level accounting for empirical dispersion correction and intrinsic anionic environment by perchlorate ions. The exchange parameter between the open-shell singlet and triplet states of the studied complexes has been estimated by broken symmetry DFT calculations. The mechanism of spin-spin exchange interaction between the unpaired electrons via the σ-bond aliphatic chain (Gusev et al., 2015) is confirmed. Instead, a anion-induced mechanism is proposed which means that the anionic grid participates in the exchange interaction between the unpaired electrons.
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| 4. |
- Baryshnikov, Gleb V., et al.
(author)
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Benzoannelated aza-, oxa- and azaoxa[8]circulenes as promising blue organic emitters
- 2016
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In: Physical Chemistry, Chemical Physics - PCCP. - : ROYAL SOC CHEMISTRY. - 1463-9076 .- 1463-9084. ; 18:40, s. 28040-28051
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Journal article (peer-reviewed)abstract
- In the present work, we studied the synergetic effect of benzoannelation and NH/O-substitution for enhancing the absorption intensity in a series of novel designed benzoannelated aza- and oxa[8]circulenes. Semi-empirical estimations of the fluorescence rate constants allowed us to determine the most promising fluorophores among all the possible benzoannelated aza-, oxa- and mixed azaoza[8]circulenes. Among them, para-dibenzoannelated [8]circulenes demonstrated the most intense light absorption and emission due to the prevailing role of the linear acene chromophore. Calculated phi(fl) values are in complete agreement with experimental data for a number of already synthesized circulenes. Thus, we believe that the most promising circulenes designed in this study can demonstrate an intensive fluorescence in the case of their successful synthesis, which in turn could be extremely useful for the fabrication of future blue OLEDs. Special attention is devoted to the aromaticity features and peculiarities of the absorption spectra for the two highly-symmetrical (D-4h ground state symmetry) pi-isoelectronic species as well as the so-called tetrabenzotetraaza[8]circulene and tetrabenzotetraoxa[8]circulene molecules. Both of them are characterized by rich electronic spectra, which can be assigned only by taking into account the vibronic coarse structure of the first electronic absorption band; the 0-1 and 0-2 transitions were found to be active in the absorption spectrum in complete agreement with experimental data obtained for both energy and intensity. The corresponding promotive vibrational modes have been determined and their vibronic activity estimated using the Franck-Condon approximation.
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| 5. |
- Baryshnikov, Gleb V., et al.
(author)
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Optical tuning of tetrabenzo[8]circulene derivatives through pseudorotational conformational isomerization
- 2018
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In: Dyes and pigments. - : Elsevier. - 0143-7208 .- 1873-3743. ; 151, s. 372-379
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Journal article (peer-reviewed)abstract
- In order to further search efficient [8]circulene materials for OLED applications we have theoretically investigated the structure and electronic, absorption spectra of functionalized tetrabenzo[8]circulenes with different substituents in the outer perimeter. These hydrocarbon materials complement the wide family of [8]circulenes which earlier have been demonstrated to possess promising emissive and exciplex-forming properties suitable for organic light emitting diodes. The hydrocarbon tetrabenzo[8]circulenes show saddle shape of the molecular skeleton which can exist in two different conformations with different curvatures of the macrocycle. The aromaticity, electronic structure and orbital pattern are found to be principally different for these two isomers, where the global minimum isomer is weakly antiaromatic and electronically less stable comparing with the non-aromatic local minimum structure. The absorption spectra are also very different: the global minimum structure is more active in the long-wavelength region while the local minimum isomer shows absorption only at short wavelengths. Our computational findings suggest a new concept for optical tuning of curved [8]circulenes through conformational isomerization and aromaticity control, thus through structural variations without changing the molecular composition. Based on this principle we have designed novel functionalized [8]circulenes with promising fluorescence activity.
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| 6. |
- Baryshnikov, Glib V., et al.
(author)
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Solvatochromic effect in absorption and emission spectra of star-shaped bipolar derivatives of 1,3,5-triazine and carbazole. A time-dependent density functional study
- 2017
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In: Journal of Molecular Modeling. - : Springer-Verlag New York. - 1610-2940 .- 0948-5023. ; 23:2
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Journal article (peer-reviewed)abstract
- A series of three star-shaped compounds containing both donor (carbazole) and acceptor (2,4,6-triphenyl-1,3,5-triazine) moieties linked through various linking bridges was studied theoretically at the linear response TD-DFT level of theory to describe their absorption and fluorescence spectra. The concept of a localized charge-transfer excited state has been applied successfully to explain the observed strong solvatochromic effect in the emission spectra of the studied molecules, which can be utilized for the fabrication of color tunable solution-processable OLEDs. The concept is in particularly applicable to donor–acceptor species with a C3 symmetry point group where the static dipole moment changes dramatically upon electronic excitation. An important peculiarity of the studied molecules is that they are characterized by non-zero values of the HOMO and LUMO orbitals in the same common part of molecular space that provides a large electric dipole transition moment for both light absorption and emission. [Figure not available: see fulltext.]
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| 7. |
- Baryshnikov, Gleb V., et al.
(author)
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Substituent-sensitive fluorescence of sequentially N-alkylated tetrabenzotetraaza[8]circulenes
- 2017
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In: New Journal of Chemistry. - : Royal Society of Chemistry. - 1144-0546 .- 1369-9261. ; 41:15, s. 7621-7625
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Journal article (peer-reviewed)abstract
- We explore the use of substituent-sensitive balance between fluorescence and non-radiative decay as a tool for optical tuning of promising materials for organic light emitting diode applications. A series of N-butylated tetrabenzotetraaza[8]circulenes is studied computationally in order to explain the gradual decrease of fluorescence intensity with the increase of the substituent number. The inter-system crossing probability is found to increase upon the gradual substitution of the circulene macrocycle as a result of the decrease of the S-1-T-1 energy gap due to the deformation of the tetrabenzotetraaza[8] circulenes and therefore the distortion of the pi-conjugation within the macrocycles. In contrast, the S-1-T-1 spin-orbit coupling matrix elements are quite insensitive to the number of outer substituents. As a result, the fluorescence-responsible pi pi(star) transition becomes less intense and the fluorescence rate constant decreases.
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| 8. |
- Baryshnikov, Gleb V., et al.
(author)
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Vibronic absorption spectra of the angular fused bisindolo- and biscarbazoloanthracene blue fluorophores for OLED applications
- 2018
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In: Chemical Physics. - : Elsevier. - 0301-0104 .- 1873-4421. ; 513, s. 105-111
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Journal article (peer-reviewed)abstract
- An in-depth analysis of the vibronic absorption spectra for the recently synthesized blue-fluorescent OLED emitters bis[(1,2)(5,6)]indoloanthracene and biscarbazolo[3,4-a:3',4'-h]anthracene has been carried out computationally at the density functional theory level within the Franck-Condon approximation. These molecules are characterized by extended and rich electronic absorption spectra with most absorption bands being of vibronic origin. The first excited singlet state of bis[(1,2)(5,6)]indoloanthracene compound demonstrates a clear observable double-peak vibronic progression for two different active modes in the absorption spectrum, while the S-2 state is vibronically inactive. In contrast, for the larger biscarbazolo[3,4-a:3',4'-h]anthracene compound the S-0 -> S-2 transition demonstrates well-resolved intense vibronic bands which overlap the less intense progressions of few modes in the S-0 -> S-1 transition. We have also found, that even the higher-lying and very intense S-0 -> S-4 and S-0 -> S-5 transitions for bis[(1,2)(5,6)]indoloanthracene and biscarbazolo[3,4-a:3',4'-h]anthracene, respectively, are characterized by clear vibronic progressions in excellent agreement with experimental spectra.
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| 9. |
- Bucinskas, Audrius, et al.
(author)
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Can attachment of tert-butyl substituents to methoxycarbazole moiety induce efficient TADF in diphenylsulfone-based blue OLED emitters?
- 2020
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In: Organic electronics. - : ELSEVIER. - 1566-1199 .- 1878-5530. ; 86
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Journal article (peer-reviewed)abstract
- A new series of TADF emitters with donor-acceptor or donor-acceptor-donor structure containing 2,7-dimethoxycarbazole donor moiety and diphenylsulfone acceptor unit were synthesized and employed in non-doped sky-blue organic light emitting diodes with the external quantum efficiency reaching 9.0%. Thermal, optical and photophysical properties of for D-A and D-A-D compounds containing one or two tert-butyl groups attached to C-3 and C-6 positions of 2,7-dimethoxycarbazole moiety were studied and compared with those of the corresponding compounds containing no tert-butyl groups. Studies of photophysical properties of the compounds confirmed TADF nature of their emission. Computational studies revealed that small modification of the donor moiety could have a significant impact on the TADF mechanism turning it from vibronically induced TADF mediated by the T-2 state to the common TADF which occurs through the direct reverse intersystem crossing between the S-1 and T-1 states. New principle of purposeful of molecular design of TADF emitters with controlled efficiency of reverse intersystem crossing by only small functionalization of donor fragments is proposed.
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| 10. |
- Engström, Maria, et al.
(author)
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Linear response calculations of electronic g-factors and spin-rotational coupling constants for diatomic molecules with a triplet ground state
- 1998
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In: Chemical Physics. - : Elsevier. - 0301-0104 .- 1873-4421. ; 237:1-2, s. 149-158
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Journal article (peer-reviewed)abstract
- Electronic g-factors for ESR spectra of a number of diatomic molecules with a ground X3Σ- state and their electronic spin-rotational coupling constants have been calculated by a linear response method. General expressions are used for the second order correction to the electronic g-factor which account for spin-orbit coupling induced admixtures from all excited triplet states to the ground state orbital magnetism. First order corrections - the spin-Zeeman kinetic energy contribution and the one-electron spin-Zeeman gauge contribution - to the g-factor are also accounted for. Calculated g-factors and spin-rotational coupling constants are in a good agreement with available experimental data. In particular, the positive, anomalous, sign of the spin-rotational coupling constant of the PF radical is reproduced.
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