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The luminescent properties 1‐(9‐antryl)butane‐1,3‐dione (1) have been investigated by means of time resolved and steady state luminescence. The results have been analyzed via the method of time‐dependent density functional theory (TD DFT). It has been shown that for compound 1 there are two forms of enol, A and B, which differ in the position of the luminescence bands. For compound 1 in polar solvents, the dual luminescence has been detected: the structured band of 420 nm and the wide diffuse band at 530 nm. In nonpolar solvents, only a broad band at 530 nm was observed. A long‐wavelength band at 530 nm was attributed to the processes of Excited‐State Intramolecular Proton Transfer (ESIPT) and Twisted Intramolecular Charge Transfer (TICT). For compound 1 in acetone, the intensity of the short‐wavelength band of the enol B increased along with the temperature increase. [ABSTRACT FROM AUTHOR]

Theoretical chemistry provides a panel of powerful tools to investigate the geometries and electronic properties of excited states. However, it is necessary to benchmark the accuracy of existing models to determine the range of their applicability and accountability. In the present work, the performance of two related methodologies in this context, symmetry-adapted cluster-configuration interaction (SAC-CI) and time-dependent double-hybrid density functional theory (TD-DHDFT), is compared in detail for the calculation of absorption and fluorescence energies of small organic molecules and π-conjugated heteroaromatic compounds. Pragmatically, for the SAC-CI calculations the singles and doubles linked excitation operators are considered in the wave functions. On the other hand, for the TD-DHDFT calculations the linear-response Tamm–Dancoff formalism has been imposed. The considered DH density functionals include the approximations from both families of adjusted and non-adjusted models. Our numerical data reveal that of the tested adjusted DHs, B2-PLYP performs the best, while among the category of non-adjusted approximations the PBE0-DH functional outperforms others. Furthermore, the DH density functionals show deviations less than those obtained from SAC-CI method. Putting all the results together, the B2-PLYP and B2GP-PLYP functionals are found to be superior for overall performance. Altogether, the present contribution and recent efforts in this arena point out that besides the ground-state properties the DH approximations have also unquestionably entered into the field of excited-state calculations, where the DHDFT again comes into play and further evidence on the quality of the corresponding models is pronounced. [ABSTRACT FROM AUTHOR]

[Display omitted] • The fluoride-sensing mechanism of a fluorescent sensor is theoretically confirmed. • Calculated VTEs are in good agreements with experimental spectra. • Fluoride-sensor complex undergoes an ESPT process with a relatively high potential barrier. • ESPT alleviates the steric hindrance in the sensor and enlarges the conjugated system. • ESPT process leads to the red-shifted fluorescence upon the addition of fluoride. An understanding of the excited-state process and the sensing mechanism for specific anions can be helpful for the design and synthesis of fluorescent sensors in analytical chemistry and biotechnology. Here, we theoretically investigated the fluorescent response mechanism of a reported acylhydrazone-based fluorescent sensor (Soft Matter , 2019, 15, 6690) for fluoride recognition using the time-dependent density functional theory approach. At the M06/TZVP/SCM level, the vertical excitation energies, which were calculated based on the ground state and first singlet-state geometries of the sensor molecule, agreed well with the experimental ultraviolet–visible and fluorescence spectra. Therefore, the time-dependent density functional theory method was considered reasonable and effective. According to the frontier orbital analysis and an excited-state potential energy scan, we proposed an excited-state proton transfer mechanism for the sensor-fluorine complex, where the steric hindrance leads to a high potential barrier. The excited-state proton transfer process facilitates sensor molecule deprotonation, alleviates its steric hindrance effect and expands its conjugated system. As a result, the fluorescence emission band of the sensor molecule was red-shifted significantly with the addition of fluoride anion. Based on this fluorescence difference, the sensor could be used for fluoride anion identification. This work provides a strategy to study sensor–analyte interactions in the excited state and offers an approach to tune the fluorescence emission wavelength of sensor molecules in anionic environments. [ABSTRACT FROM AUTHOR]

In this work, the time-dependent density functional theory (TD-DFT) method was used to study the electronic excited-state dynamics of the hydrogen-bonded p-Cresol-NH-HO complex. The intermolecular hydrogen bonds O-H···N and C-O···H were demonstrated by the optimized geometric structure of the hydrogen-bonded p-Cresol-NH-HO complex. The infrared spectra (IR spectra) of the hydrogen-bonded p-Cresol-NH-HO complex in the ground and excited states were also calculated by using the density functional theory (DFT) and TD-DFT methods. It is demonstrated that hydrogen bond O-H···N can be strengthened while hydrogen bond C-O···H is weakened upon photoexcitation to the S state. The significant changes of the hydrogen bond from the calculated bond lengths in different electronic states can be observed. In addition, the spectral shifts of the stretching vibrational mode of the hydrogen-bonded O-H group in different electronic states are accounted for the hydrogen bond changes in the S state too. [ABSTRACT FROM AUTHOR]

Experimental absorption and emission spectra of benzoaza-18-crown-6-containing styryl dye and its complexes with Li, Na, and Ca are recorded. It is found that complexation causes large hypsochromic shifts of the long-wave absorption band of the dye. In addition, the spectra of Li and Na complexes exhibit an additional band or a shoulder with λ virtually coinciding with the absorption band of the free dye. Complexation also enhances the fluorescence of the dye. Simulating the structure and electronic spectra of the dye and its complexes with Li, Mg, Na, and Ca by DFT and TD DFT allowed us to explain these effects. It is found that cation coordination breaks the conjugation of the crown ether nitrogen with the chromophore, thus reducing the effective chromophore size, and the positive charge of the cation simultaneously decreases the donor nature of the amino group. This explains large hypsochromic shift of the long-wave absorption band. It is found that Li and Na complexes can form two types of conformers, with and without cation-nitrogen bond. The conformers with the cation-nitrogen bond exhibit a very strong blue shift of the absorption maximum, while the absorption spectra of the complexes without cation-nitrogen bond are almost unshifted relative to the spectra of the free dye. The ground-state recoordination of the cation in the macrocycle cavity involves the change between these two forms. Recoordination is promoted by the interaction of the cation with solvent molecules. This explains the presence of the additional long-wave band or shoulder in the spectra of the complexes. Cation-induced fluorescence enhancement is explained by the changes in the excited-state structure of the free dye and its complexes. The free dye changes its structure from the 'quinoid' form in the ground state to the 'benzenoid' form in the excited state, thus facilitating the rotation of the alkoxyaminophenyl group and causing near-degeneracy of the potential energy surfaces of the ground and excited states. This results in rapid nonradiative deactivation and fluorescence quenching. Complexation with cations reverses the dye structure to the 'benzenoid' form in the ground state and to the 'quinoid' form in the excited state thus preventing alkoxyaminophenyl group from rotation, which results in fluorescence enhancement. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 [ABSTRACT FROM AUTHOR]

The effects of substituents on the electronic structures of di(thienylene vinylene) (2TV) in ground and excited states are studied using density functional theory (DFT) and time-dependent DFT (TD-DFT), respectively. A representative set of electron donating groups (amino, methoxy and methyl) and withdrawing groups (acetylene, cyano and nitro) are introduced on the vinylene and thienyl moieties to investigate the influence of substituents. Bulk solvent effects are also taken into account by means of the polarizable continuum model (PCM). In contrast to the aromatic structures of 2TV and its derivatives in their ground (S0) states, the electronic structures of first singlet excited (S1) states are rather delocalized. The electron-donating/withdrawing capability, position and number of substituents are important factors in tuning the vertical S0 → S1 absorption energies and S1 → S0 emission energies of 2TV derivatives. The NO2- and NH2-substituents exert significant effects on the geometries of both ground and excited states and hence the absorption and photoluminescence (PL) emission spectra. The solvent polarity introduces modest influence on the excitation energies for most of the 2TV derivatives. But the absorption and PL emission spectra of nitro-substituted 2TV exhibit noticeable red shifts as the medium polarity increases. Copyright © 2008 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: The lower singlet excited states for 4′-N-dimethylamino-3-hydroxyflavone (DMA3HF) have been investigated. Theoretical calculations have been performed by using time-dependent density functional theory. The B3LYP and MPW1PW91 functionals with 6-31G(d,p) basis set have been used to compute transition energies. Ground-state geometries are optimized by using density functional theory with both B3LYP and MPW1PW91 functionals combined with 6-31G(d,p) basis set. The first excited state geometries are optimized by using configuration interaction all single-excitations methods with 6-31G(d,p). Vertical absorption energy and excited state electronic dipole moments calculations show that the singlet excited states S1 of the normal of DMA3HF has the character of a large charge separation and effective charge transfer. Calculated emission energies for both the normal and tautomer show a large Stokes shift between the absorption and fluorescence maxima. The present calculations suggest that DMA3HF appears dual fluorescence in gas phase. Our results obtained explain the strong ‘dual-fluorescence’ feature that involves the excited-state intramolecular proton transfer and charge transfer of DMA3HF. [Copyright &y& Elsevier]

Abstract: Poly(3,4-ethylenedioxythiophene) (PEDOT) doped with poly(4-styrenesulphonate) (PSS) has been widely used in light-emitting devices as hole transport layer and in photovoltaic devices as hole-collecting layer. In the present study, various quantum chemical calculations were carried out for the investigation of low-lying excited states of ethylenedioxythiophene (EDOT), and styrenesulphonic acid. The lowest adiabatic transition energies were calculated using configuration interaction singles method. The time-dependent density functional theory was also applied for the calculation of the vertical excitation energies. Differential self-consistent-field-based density functional theory method is well known to show good performance for the geometry of excited state and hence it was also applied to study of the first singlet excited state. In addition to the calculation of the monomer, the electronic properties of PEDOT were calculated by periodic density functional theory method and the result is in good agreement with the experimental observation. [Copyright &y& Elsevier]

The geometrical optimization of Oxophosphorus triazatetrabenzcorrole (POTBC) has been studied at Density Functional Theory (DFT) level using various basis sets. The results at Hartree–Fock (HF) level were used for comparison. The results calculated at the HF and B3LYP levels are very different. The geometry at B3LYP level has Cs structure while at HF level it has no symmetry. The structure at the DFT level is reliable because DFT includes an electron correlation correction. The HOMO-1 of POTBC is separated from HOMO-2 by a large gap. As a result the excited states of POTBC can be interpreted by the Gouterman''s four-orbital model. It has been proved by TDDFT calculations of the excited states of POTBC. It can be concluded that the structure of POTBC is similar to that of phthalocyanine (Pc), while its orbital energies are similar to porphyrin''s [Copyright &y& Elsevier]