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In this research, the ground (µg) and excited (µe) state dipole moments of metformin hydrochlorides were determined using Lippert-Mataga, Bakhshiev's, Kawski-Chamma-Viallet, and Reichardt models from fluorescence emission and UV-Vis absorption spectra in various solvents. From solvatochromic effects the calculated excited (µe) dipole moment of metformin hydrochloride were, 8.55 D, 8.34 D, 6.08 D, and 6.40 D using the Lippert-Mataga, Bakhshiev's, Kawski-Chamma-Viallet and Reichardt models respectively. The results also indicated that the dipole moment at the ground state is smaller than the excited state. This is due to solvent polarity having a stronger effect on fluorescence emission than absorption spectra. Similarly, from density functional theory, the calculated ground and excited states dipole moments of metformin hydrochloride using (DFT-B3LYP- 3-21+G*(μg = 10.02 D and μe = 11.94 D), DFT-B3LYP- 6-31+G (d, p) (μg = 8.44 D and μe = 10.87 D), and DFT-B3LYP- 6-311+G (d, p) (μg = 8.24 D and μe = 18.74 D)) analyzed by Gaussian 09W. From the optimized geometry of the molecule, the HOMO-LUMO energy band gap of metformin hydrochloride were computed using DFT [DFT-B3LYP- 3-21+G*(5.51 eV), DFT-B3LYP- 6-31+G (d, p) (5.66 eV), and DFT-B3LYP- 6-311+G (d, p) (5.70 eV)] respectively. [ABSTRACT FROM AUTHOR]

spectral dependencies of the electroluminescence intensity of a microdisk laser with a diameter of 31 μm with active region based on InAs/InGaAs quantum dots, operating in the continuous-wave regime, are investigated in a wide range of injection currents. Simultaneous lasing through the ground and excited states of quantum dots under intense excitation is demonstrated in injection microdisk laser for the first time. At low pumping powers lasing occurs via ground states of quantum dots only. [ABSTRACT FROM AUTHOR]

It is shown that, like conventional diffuse fluorescence spectra and despite the complex mechanism of formation of the excited state, the chemi- and bioluminescence spectra contain information about the frequency of the purely electronic (vertical) transition of the emitting molecules and the degree of homogeneity of their ensemble. As in the case of ordinary diffuse luminescence spectra, the frequency of a purely electronic transition is shifted significantly toward the short wavelength side (by almost the half-width of the band) from the maximum of the fluorescence spectrum. An example of the separation of the overlapping spectra using the position of a short-wavelength purely electronic transition is presented. [ABSTRACT FROM AUTHOR]

The protolytic equilibrium of the excited states of fluorescein depends not only on the equilibrium in the ground state, but also on the efficiency of photoexcitation, relaxation, and proton transfer in the excited state. Due to rate-competing radiative and non-radiative processes occurring in a mixture of protolytic forms, there is still a problem of identifying the fluorescent characteristics of individual forms of fluorescein. In this work, the steady-state distribution of the concentrations of the ground and excited states of the cation, a number of tautomers of the neutral form, monoanion, and dianion of fluorescein under continuous photoexcitation was simulated. The pH values of the predominant existence of individual protolytic forms in the excited states were determined, which were confirmed by steady-state fluorescence measurements. Possible reasons for the discrepancies in the published data on the fluorescent properties of individual protolytic forms of fluorescein are discussed and refined data on the spectral shapes and lifetimes of the quinoid and monoanion of fluorescein are obtained. [ABSTRACT FROM AUTHOR]

Properties of 0+ excited states generated by pairing and quadrupole-quadrupole forces in some rare-earth isotopes are investigated. Energies of the 0+ states, probabilities of the E(0) and E(2) transitions, Rasmussen parameters X, and effective cross sections of two-nucleon transfer reactions have been calculated taking into account mixing of the excited states with different Kπ values. The contribution of mixing of the excited states underestimates values of the calculated physical quantities. [ABSTRACT FROM AUTHOR]

The simultaneous quantum-chemical and spectral investigations of the possible relaxation pathways in the excited state for the two α,ω-di-substituted polyenes were performed. Lengthening of the polymethine chain is accompanied by the considerable decreasing of the first electron transition and hence is manifested as the bathochromic shift of both absorption and fluorescence spectra; however, the nature of transition does not change. It is established that the considerable changes of the bond lengths in polymethine chain for both vinylogs in the excited state cause firstly the appearance of the fast component in short wavelengths spectral region; after relaxation, the intensity of the fast component decreases, and it disappears, but then the spectral band, shifted bathochromically, appears, so that its maximum coincide with the band maximum in the steady-state fluorescence maximum, what corresponds to the final symmetrical relaxation of bond lengths. The parallel quantum-chemical calculation shows that two highest levels are mainly formed by the donor levels of both terminal groups and hence twice occupied splitting levels. Upon excitation, one of the splitting MO (HOMO) becomes single occupied; this causes the molecule in the excited state to be unstable and could transform it to the unsymmetrical form. Such relaxation path is confirmed by the time-resolved spectra: the spectral band in both molecules, with the different polymethine chains, undergoes the subsequent bathochromical shifting. [ABSTRACT FROM AUTHOR]

To investigate substitution effects on excited-state intermolecular proton transfer (ESPT) reactions as well as acidity of proton donating fragments in the ground state, we synthesized substituted anthracen-2-yl-3-phenylurea derivatives that form a hydrogen bonds with acetate anions and undergo ESPT reaction. Fluorescence lifetime measurements and their kinetic analyses revealed that the trifluoromethyl group on the phenyl ring as an electron-withdrawing group caused a slow ESPT reaction despite an increase in the acidity of the N–H fragment in the ground state. In contrast, the methoxy group as a donating group leads to a fast ESPT reaction despite a reduction of the acidity of the N–H fragment in the ground state. These effects of substituents on ESPT reaction are due to their influence on the charge transfer reaction, which occurs from the N–H fragment to the anthryl ring to increase the acidity of N–H followed by ESPT reaction, over the urea unit by a combination of resonance and inductive effects. These opposing effects of substituents on the acidity of the urea unit in the ground and excited states provide an important insight in balancing the reactivity of proton transfer reaction in both the excited and ground states. [ABSTRACT FROM AUTHOR]

A simple structural comparison method based on relative changes of internal coordinates among different electronic states is presented. As such, any electronic state with respect to the ground state could be represented as a point on two dimensions. Although this analysis is not based on quantum mechanically "correct" description of molecules based on electron density and thus employs geometries rather than topologies, it might have advantages over overlaying procedures in resolving small differences as well as quantification of similarity/dissimilarity. More importantly correlations of structural similarity with luminescence properties were discussed for popular π-chromophores by studying S0, S1, and T1 states of indole, coumarin, BODIPY, and naphthalene. A qualitative difference on the structural similarity plane in spanning of S0 → S1 and S0 → T1 coordinate deformation vectors for popular fluorophores was identified. This emphasized a well-protected/separated S1 state to be a key feature of an efficient fluorophore. Our calculations on excited states suggest that, a quick screening of structure–luminescence relationships is possible. Structural features of efficient fluorophores outlined in this work can hopefully help rational designing of chromophore cores with desired luminescence properties. [ABSTRACT FROM AUTHOR]

Details concerning the energetics and structure of the ion pair in gaseous chloroethane, obtained at the multi-reference configuration interaction with singles and doubles (MR-CISD) level, are given. It is formed in the third excited state (31A′), and it can be classified as a hydrogen-bonded contact ion pair, although from its total binding energy of 3.28 eV (including extensivity corrections, at the MR-CISD + Q level with the aug-cc-pVTZ basis set, and including zero-point energy corrections) only 0.14 eV is due to an underlying hydrogen bond. It is a highly polar structure, with a dipole moment of 9.56 D. As compared to previous systems for which the same type of bond has been observed, it has a much lower hydrogen-bond energy and a much larger distance between the charge centers. The three lowest frequency vibrational modes of the HBCIP correspond to intermolecular cation–anion modes. The structure here obtained brings important structural questions for HCFCs derived from chloroethane. [ABSTRACT FROM AUTHOR]

The energy eigenvalues for confined H 2 + molecule are computed by using the variational method. The approach proposed here uses a trial molecular function for the ground state composed of a linear combination of atomic orbitals for confined hydrogen atom; for other states, we build the trial molecular eigenfunctions inspired in atomic orbitals and by using the orthogonality of the wave functions. The molecule is confined in an impenetrable prolate spheroidal box. The atomic orbital for 1s state is built from a previous suggestion inspired by the factorization of the Schrödinger equation, and for 2s state, we used the Gram–Schmidt process to build a trial atomic function orthogonal with 1s trial function. The main contribution of this work is to propose new wave functions to be used for the confined hydrogen ion molecule. The results obtained are in agreement with other results present in the literature, and the trial functions proposed here can be used to study other confined molecules. [ABSTRACT FROM AUTHOR]

A series of cyclometalated platinum(II) complexes with similar molecular structures but distinct phosphorescence quantum yields were investigated. To explore the intersystem crossing (ISC) and radiative decay processes, we investigated the absorption and phosphorescence properties, spin–orbit coupling matrix elements, major ISC channels and phosphorescent transition rates. For the temperature-dependent nonradiative decay processes, the metal-centered excited states (3MC), the transition states, and the minimum energy crossing points were investigated with theoretical calculations. The way of temperature-independent nonradiative decay which has weak influence on nonradiative decay rate was also compared through the calculation of reorganization energy (λ). [ABSTRACT FROM AUTHOR]

Unconventional non-fluorescent J-aggregates of Tetracene (TC) and Naphtho[2,1,8-qra]tetracene (NT) were witnessed and their consequent dramatic quenching was unravelled by a steady state, time-resolved and transient spectroscopy in conjunction with excited state density functional calculations. The TC O-aggregate with slippage angle θ = 22. 3 ∘ < 54. 7 ∘ exhibited substantial transition dipole moment (TDM) for both lower (2.79 D) and higher (1.59 D) energy singlet excitations, while, NT formed an ideal J-aggregate (polarization angle, α ∼ 0 ∘) with a predominant TDM to only a lower excitonic state (2.69 D). Subsequently, their unusual quenching was quantified with large drops in the photoluminescence quantum yields (PLQY) from 0.116 to 0.002 upon TC O-aggregation and from 0.478 to 0.038 upon NT J-aggregation. These intense PL drops were systematically investigated for possible occurrence of excimer-like emission quenching and/or photo-degradation of the TC core unit. In view of the TC O-aggregates exhibiting a perfect energetic balance between the singlet (2.34 eV) and triplet (1.28 eV) energies for singlet fission (SF) and a concomitant delayed fluorescence signal, their S 1 decay characteristics were attributed to SF followed by an inverse triplet-triplet recombination. In contrast, the energetic imbalance ( E (S 1) < 2xE (T 1) ) in NT J-aggregates permitted only forward process of SF and the resulting long-lived triplet formation was traced with a positive transient absorption ( T 1 → T n) band at 500 nm. Accordingly, the singlet excited state (S 1) dynamics of TC O- and NT J-aggregates, being largely dominated by SF, depicted a depleted S 1 population, accounting for the large deviation from aggregation induced enhanced emission, exhibited by classical dye J-aggregates. Unconventional O- and J -aggregates of Tetracene and Naphtho[2,1,8-qra]tetracene showed non-fluorescent behaviour whose singlet excited state (S 1) dynamics was largely governed by fast Singlet Fission decay, accounting for atypical deviation from the well-established aggregation induced enhanced emission from classical J-aggregates. [ABSTRACT FROM AUTHOR]

A variational solution to the eigenvalue problem for the Hamiltonian H, with orthogonality restrictions on eigenvectors of H to the vector H ∣ Φ0〉, where ∣Φ0〉 is an approximate ground-state vector, is proposed as a means to calculate excited states. The asymptotic projection (AP) method proposed previously is further developed and applied to solve this problem in a simple way. We demonstrate that the AP methodology does not require an evaluation of the matrix elements of operator H2, whereas conventional approaches—such as the elimination of off-diagonal Lagrange multipliers method, projection operator techniques, and other methods—do. It is shown, based on the results obtained for the single-electron molecular ions H2+, HeH2+, and H32+, that applying the new method to determine excited-state wavefunctions yields the upper bounds for excited-state energies. We demonstrate that regardless of whether the orthogonality constraint for states (〈Φ| Φ0〉 = 0) is applied, the zero-coupling constraint (〈Φ| H| Φ0〉 = 0) is imposed, or both of these restrictions are enforced simultaneously, practically the same excited-state energy is obtained if the basis set is almost complete. For the systems considered here, all schemes are capable of giving a sub-μhartree level of accuracy for the ground and excited states computed with different basis sets. [ABSTRACT FROM AUTHOR]