Experimental Transition Energies Research Articles

Application of QSPR-MLR methodology to solvatochromic behavior of quinoline in binary solvent HBD/DMF mixtures

Quantitative Structure-Property Relationship methodology was applied successfully to experimental molar transition energies of quinoline, published before, in order to achieve a better understanding about the predominant quinoline–solvent interactions. Internal and external model validations were performed showing a high predictive ability of the selected multiple linear relationship. The wavenumbers of maximum absorbance of five dyes UV–vis spectra in methanol/dimethylformamide, propan-1-ol/dimethylformamide and pentan-1-ol/dimethylformamide mixtures, and in pure solvents, were experimentally determined, at 298.15 K, with the aim of calculating the Kamlet and Taft solvatochromic parameters ( π ⁎, α and β). Refractive indices of those mixtures were also calculated, to evaluate the Lorentz–Lorenz function values, g( n D). The chosen solvatochromic response model of quinoline suggests the dominance of the dipolarity/polarizability ( π ⁎) and the basicity ( β) parameters followed by the E T N one (predominantly a measure of the solvent acidity). The former parameter contributes to a higher stabilization of the ground state and the two latter ones to a greater stabilization of the quinoline Frank–Condon excited state.

Calculation of the charge transfer transition energy of the mesitylene–ICl complex by ab initio and TDDFT methods: Comparison with other methylbenzene–ICl complexes

Of the four plausible isomeric structures of the mesitylene–ICl charge transfer (CT) complex, the most feasible one was determined by a detailed ab initio and DFT study at the HF, B3LYP and MPW1PW91 levels using the 6-31++G(d,p) basis set. Potential energy surface scans followed by frequency calculation and full optimization revealed that the I–Cl bond, with its I atom oriented towards the aromatic ring, stands vertically above an unsubstituted C-atom, being inclined at about 6° to the C 3-axis. Complexation increases the I–Cl bond length. Correction for basis set superposition error through a counterpoise calculation yields a binding energy close to the experimental value. The electronic CT transition energy (hν CT) with this ground-state structure as input was calculated in vacuo by the CIS method and in carbon tetrachloride medium by the TDDFT method under the polarizable continuum model. In a similar way the values of hν CT were calculated for complexes of ICl with p-xylene, durene and hexamethylbenzene. Throughout the series of methylbenzene complexes, the TDDFT-calculated values of hν CT were less than the experimental values and such underestimation may be attributed to the inherent difficulties of DFT to take into account long-range interactions. However, the trend of the variation of hν CT with the number and position of methyl groups in the series was reasonably similar to the trend followed by the experimental CT transition energies.

Electromodulation spectroscopy of In 0.53Ga 0.47As/In 0.53Ga 0.23Al 0.24As quantum wells

In 0.53Ga 0.47As/In 0.53Ga 0.23Al 0.24As quantum wells (QWs) of various widths have been grown by molecular beam epitaxy on the InP substrate and investigated by electromodulation spectroscopy, i.e. photoreflectance (PR) and contactless electroreflectance (CER). The optical transitions related to the QW barrier and the QW ground and excited states have been clearly observed in PR and CER spectra. The experimental QW transition energies have been compared with theoretical predictions based on an effective mass formalism model. A good agreement between experimental data and theoretical calculations has been observed when the conduction band offset for the In 0.53Ga 0.47As/In 0.53Ga 0.23Al 0.24As interface equals ∼60%. In addition, it has been concluded that the conduction band offset for the In 0.53Ga 0.23Al 0.24As/InP interface is close to zero. The obtained results show that InGa(Al)As alloys are very promising materials in the band gap engineering for structures grown on InP substrate.

TD-DFT benchmark for indigoïd dyes

In this paper, we assess the efficiency of more than 20 functionals for reproducing the experimental absorption wavelength of a large set indigo derivatives (thioindigo, selenoindigo, indirubin, isoindigo,...). The pros and cons of each functional is analysed in terms of, on the one hand, the accuracy with respect to the experimental transition energies, and, on the other hand, the consistency of the predicted rankings. It turns out that global hybrids including between 20% and 25% of exact exchange yield the smallest mean absolute deviations. Functionals with a larger percentage of exact exchange ( ∼ 50%) or range-separated hybrids deliver larger absolute errors, but improve the linear correlation between experimental and theoretical values.

Photoexcitation screening of the built-in electric field in ZnO single quantum wells

ZnO/Mg0.22Zn0.78O quantum wells were studied by excitation-intensity-dependent luminescence at 10 K. The samples were grown by laser molecular-beam epitaxy on ScAlMgO4 substrates to evaluate the well width dependence (1 to 10 nm) of exciton transition energies. Under weak excitation, the photoluminescence shows a quantum-confined Stark effect for the wide wells. The well width dependences of the experimental transition energies are compared with previously reported calculations to evaluate the electric field due to spontaneous and piezoelectric polarizations. The internal electric field is comparable with 650 kV/cm. With an increase in excitation intensity, blueshift of the luminescence was observed, suggesting photoexcitation screening of electric fields.

Time-Dependent Density Functional Theory As a Tool for Isomer Assignments of Hydrogen-Bonded Solute·Solvent Clusters

Can isomer structures of hydrogen-bonded solute x solvent clusters be assigned by correlating gas-phase experimental S0 <--> S1 transitions with vertical or adiabatic excitation energies calculated by time-dependent density functional theory (TD-DFT)? We study this question for 7-hydroxyquinoline (7HQ), for which an experimental database of 19 complexes and clusters is available. The main advantage of the adiabatic TD-B3LYP S0 <--> S1 excitations is the small absolute error compared to experiment, while for the calculated vertical excitations, the average offset is +1810 cm(-1). However, the empirically adjusted vertical excitations correlate more closely with the experimental transition energies, with a standard deviation of sigma = 72 cm(-1). For the analogous correlation with calculated adiabatic TD-DFT excitations, the standard deviation is sigma = 157 cm(-1). The vertical and adiabatic TD-DFT correlation methods are applied for the identification of isomers of the 7-hydroxyquinoline.(MeOH) n , n = 1-3 clusters [Matsumoto, Y.; Ebata, T.; Mikami, N. J. Phys. Chem. B 2002, 106, 5591]. These confirm that the vertical TD-DFT/experimental correlation yields more effective isomer assignments.

Room temperature contactless electroreflectance of the ground and excited state transitions in Ga0.76In0.24As0.08Sb0.92∕GaSb single quantum wells of various widths

The optical transitions in Ga0.76In0.24As0.08Sb0.92∕GaSb quantum wells with the width varying from 10to21nm were studied by room temperature contactless electroreflectance (CER). In addition to the quantum well (QW) ground state transition (11H), the 22H and 33H transitions (where klH denotes transition between the kth heavy hole and the lth electron subbands) have been clearly observed in CER spectra. The experimental QW transition energies were compared with theoretical predictions based on an effective mass formalism model. It has been concluded that this QW is type I for both electron and holes and the conduction band offset for the unstrained Ga0.76In0.24As0.08Sb0.92∕GaSb interface equals ∼90%.

Characteristics of strained GaAs1−ySby (0.16 ≤ y ≤ 0.69) quantum wells on InP substrates

Pseudomorphic GaAs1−ySby quantum wells with 0.16 ≤ y ≤ 0.69 on (0 0 1) InP substrates have been grown using metal–organic chemical vapour deposition. High resolution x-ray diffraction and transmission electron microscopy analysis are used to quantify the layer thicknesses and compositions. Studies of the optical properties suggest that a transition from type-I to type-II band alignment occurs at an antimony concentration of approximately y = 0.30. The interband optical transition energies simulated using a ten-band k · p Hamiltonian are compared with the experimental values deduced from photoluminescence spectroscopy. The valence band offset bowing parameter is evaluated in the context of the experimental transition energies. For low Sb-contents, reasonable agreement (<7% deviation) is achieved between theory and experiment for the primary optical transitions. However, at higher Sb-content, there is significant deviation between the measured transition energies and the k · p based theory, possibly a result of a non-ideal interface and/or heterogeneous ternary well.

TD-DFT Performance for the Visible Absorption Spectra of Organic Dyes: Conventional versus Long-Range Hybrids.

The π → π* transitions of more than 100 organic dyes from the major classes of chromophores (quinones, diazo, ...) have been investigated using a Time-Dependent Density Functional Theory (TD-DFT) procedure relying on large atomic basis sets and the systematic modeling of solvent effects. These calculations have been performed with pure (PBE) as well as conventional (PBE0) and long-range (LR) corrected hybrid functionals (LC-PBE, LC-ωPBE, and CAM-B3LYP). The computed wavelengths are systematically guided by the percentage of exact exchange included at intermediate interelectronic distance, i.e., the λmax value always follows the PBE > PBE0 > CAM-B3LYP > LC-PBE > LC-ωPBE > HF sequence. The functional giving the best estimates of the experimental transition energies may vary, but PBE0 and CAM-B3LYP tend to outperform all other approaches. The latter functional is shown to be especially adequate to treat molecules with delocalized excited states. The mean absolute error provided by PBE0 is 22 nm (0.14 eV) with no deviation exceeding 100 nm (0.50 eV): PBE0 is able to deliver reasonable estimates of the color of most organic dyes of practical or industrial interest. By using a calibration curve, we found that the LR functionals systematically allow an even more consistent description of the low-lying excited-state energies than the conventional hybrids. Indeed, linearly corrected LR approaches yield an average error of 10 nm for each dye family. Therefore, when such statistical treatments can be designed for given sets of dyes, a simple and rapid theoretical procedure allows both a chemically sound and a numerically accurate description of the absorption wavelengths.

Theoretical Characterization of a Tridentate Photochromic Pt(II) Complex Using Density Functional Theory Methods.

Density functional theory methods have been used to characterize a tridentate photochromic Pt(II) complex [Pt(AAA)Cl], its acetonitrile complex [Pt(AAA)Cl·CH3CN], and the transition state in the complexation reaction. B3LYP/6-31G* (effective core potential for Pt) optimized geometries of Pt(AAA)Cl and Pt(AAA)Cl·CH3CN are found to be in reasonably good agreement with most of the applicable parameters for the available experimental crystal structures of Pt(AAA)Cl and a Pt(AAA)Cl-triphenylphoshine complex, with the exception of one of the dihedral angles, the deviation of which is determined to be due to a steric cis versus trans effect. Vibrational frequencies are calculated for Pt(AAA)Cl and cis-Pt(AAA)Cl·CH3CN, and the predicted shift in the benzaldehyde carbonyl frequency is found to be in line with that observed experimentally. Singlet vertical excitation energies are calculated for Pt(AAA)Cl and cis-Pt(AAA)Cl·CH3CN using time-dependent density-functional theory and are found to be in good agreement with the experimental transition energies, although for cis-Pt(AAA)Cl·CH3CN, the calculations suggest a reassignment of the experimental S1 and S2 transitions. Single point energies are calculated at the B3LYP/6-311+G(2d,2p) level (effective core potential for Pt) and the calculations predict the complexation reaction (dark reaction) to be exothermic and, after a correction to the entropy, to be exoergic at 298 K and to proceed with a reasonable activation energy. Based on singlet and triplet vertical excitation energies, it is speculated that the photoreaction occurs via an intersystem crossing from S1 to T1 for cis-Pt(AAA)Cl·CH3CN followed by an adiabatic reaction along the T1 surface and then nonradiative intersystem crossing to the S0 state of Pt(AAA)Cl.

Dependence of exciton transition energy of single-walled carbon nanotubes on surrounding dielectric materials

We theoretically investigate the environmental effect for optical transition energies of single-walled carbon nanotubes (SWNTs), by calculating the exciton transition energies of SWNTs. The static dielectric constants used in the exciton calculation can be expressed as a function of the dielectric constants of the surrounding material and that of the SWNT, in which the static and dynamic dielectric constants of the SWNT represent the screening effect of core electrons and the valence π electrons, respectively. The calculated results reproduce the environmental effect of the experimental transition energies for various surrounding materials and for various diameters of SWNTs.

Ground and excited state transitions in as-grown Ga0.64In0.36N0.046As0.954 quantum wells studied by contactless electroreflectance

The optical transitions of as-grown Ga0.64In0.36N0.046As0.954 multiple quantum wells grown at the low temperature of 375°C were studied by contactless electroreflectance (CER). The investigation was carried out at room temperature for a set of samples having quantum well (QW) widths ranging from 3.9to8.1nm. The ground and the excited state transitions were clearly observed in CER spectra (the ground state transition was observed at the wavelength of 1.9μm for the 8.1nm wide QW). The experimental QW transition energies were compared with theoretical predictions based on an effective mass formalism model. Good agreement between experimental data and theoretical calculations has been obtained assuming that the conduction band offset for GaInNAs∕GaAs interface is 80% and the electron effective mass is 0.09m0.

Ab initio calculations of the colour of closed-ring diarylethenes: TD-DFT estimates for molecular switches

The visible absorption spectra of a series of diarylethene dyes have been evaluated by using a time-dependent density functional theory approach, explicitly taking into account bulk solvent effects. A complete basis set/functional methodological study has been performed. Using the PBE0 functional with the 6-311+G(2d,p) atomic basis set, we got a nice agreement between theoretical and experimental electronic transition energies for a 15 compound-set. The mean absolute error is limited to 0.13 eV and can further be reduced by a factor 4. On the contrary, the ZINDO//AM1 approach produces inconsistent absorption energies.

Ab initio MO study on the S 1 ← S 0 origin transition energies of polychlorodibenzofurans (PCDFs)

The geometries and energies for the S 0 and S 1 states of dibenzofuran (DF) and all 135 PCDFs were obtained using Hartree–Fock (HF) and CI-Singles (CIS) methods. The transition energies determined from HF and CIS energies were corrected for electron correlation. If the electron correlation energies for the S 0 and the S 1 state are calculated using a second-order Møller–Plesset perturbation (MP2) and a perturbative correction to CIS (termed CIS(D)) method, the S 1 ← S 0 0–0 transition energies are given with an error of 15.4–22.6%. Electron correlation corrections to the transition energies were determined from a selected set of experimental transition energies on the assumption of the following additivity rule: the electron correlation energy of each state can be partitioned into contributions from the parent molecule and substituent chlorines. The transition energies after correction for electron correlation are in good agreement with available experimental data with an error of 0.2–3.5%. The validity of the additivity rule with respect to electron correlation energy is discussed in relation to the geometry of the molecule. The findings show that the additivity rule holds within an error of 0.4%. Vertical ionization potentials, which are useful in REMPI spectral studies, were calculated using Koopmans’ theorem. The results confirmed that the S 1 ← S 0 origin transition energy is inversely proportional to the number of chlorine atoms n Cl but the ionization potential is directly proportional to n Cl.

The spectrum of optically allowed transitions from the 3p63d ground state of Ti IV

Recent experiments on the photoionization of Ti IV (Schippers S et al 2004 J. Phys. B: At. Mol. Opt. Phys. 37 L209–16) and the photorecombination of Ti V (Schippers S et al 1998 J. Phys. B: At. Mol. Opt. Phys. 31 4873–86) have obtained the excitation energies and spontaneous transition probabilities (A-values) for a number of the 3p53d2 and 3p53d4s autoionization states of Ti IV. The direct measurements of the spectrum of Ti IV excited in a vacuum spark (Ryabtsev A N et al 2005 Opt. Spectrosc. 98 519–27) have provided a more complete list of these excitation energies and the A-values for J–J transitions of these excited states to the 3p63d ground state. This paper presents ab initio calculations for the transition energies and A-values between individual J levels of the ground state of Ti IV and the J levels for both the bound (3d)6nl states and the bound and resonance states 3p53d2 and 3p53d4s. The calculations were carried with configuration interaction wavefunctions and relativistic effects were included using the Breit–Pauli approximation. Generally there is good agreement between the calculated transition energies and all the experimental transition energies. There are considerable differences between the A-values obtained by the different experimental groups and the agreement between the theoretical and experimental A-values is variable.

Spectrophotometric studies of complexation of [60]fullerene with series of aromatic hydrocarbon molecules containing flexible phenyl substituents

The absorption spectra of the electron donor–acceptor complexes of [60]fullerene with five different aromatic hydrocarbon (AH) molecules containing flexible phenyl substituents have been investigated in toluene medium. An absorption band due to charge transfer (CT) transition is observed in each case in the visible region. The experimental CT transition energies are well correlated with the vertical ionization potentials of the AHs studied (through Mulliken's equation) from which we extract degrees of charge transfer, oscillator and transition dipole strengths of the CT complexes. The degrees of CT in the ground state of the complexes have been found to be very low (0.49–0.55%). The formation constants (K) for the complexes of [60]fullerene with the aromatic hydrocarbons have been determined by UV–vis spectroscopy. Both K values and PM3 calculations on [60]fullerene/AH complexes reveal that nature of substitution in the donor moiety as well as steric compatibility with the acceptor molecule govern the process of EDA complex formation.

Spectroscopic studies of interaction of Safranine T with nonionic micelles and mixed micelles

The visible spectra of Safranine T (ST) in micellar solution of Brij 58, Tween 20 and Tween 40 and mixed micellar solution of Brij 58/Tween 20 and Brij 58/Tween 40 indicate formation of 1:1 charge transfer (CT) complex between acceptor ST and donor nonionic micelles and mixed micelles. The experimental CT transition energies are well correlated (through Mulliken's equation) with the vertical ionization potential of the donors. The solvent parameters, i.e. the intramolecular charge transfer energy E T(30) have been determined from the Stokes spectral shift. Variations of ionization potential and micropolarity in the mixed micellar region have been investigated as a function of surfactant composition and the obtained results in mixed micellar medium has been compared to the normal micelles. The critical micelle concentration (CMC) values determined at various surfactant compositions are lower than the ideal values indicating a synergistic interaction. The interaction parameter ( β) and micellar stability has been calculated using regular solution theory.

Simple Model Calculations of Spin and Quantized Alignment for the &lt;i≯A&lt;/i≯ ∼ 60–90 Superdeformed Mass Region

We have used a simple model based on the rotational energy formula E(I, K) to study the structure of the superdeformed (SD) mass region 60–90. The higher order inertial parameters A and B of such model were determined by using the Marquardt method of nonlinear least-squares routines to fit the proposed transition energies with their observed values. A good agreement between the calculated and corresponding experimental transition energies of the SD bands is obtained which supports our proposed model. In addition, the frequency dependence of the dynamic, θ(2), and static, θ(1), moments of inertia is used to determine the lowest spin (If) and the K-value of the considered SD bands; namely, 58Ni(b1), 58Cu, 59Cu(b1), 61Zn, 62Zn, 65Zn, 68Zn, 84Zr, 86Zr(b1), 88Mo(b1, b2, b3) and 89Tc. As a result of the identity exist among some of the considered SD bands, we have studied the incremental alignment and also the angular momentum alignment.

Dications of Bis-triarylamino-[2.2]paracyclophanes: Evaluation of Excited State Couplings by GMH Analysis

In this paper, we present the absorption properties of a series of bis-triarylamino-[2.2]paracyclophane diradical dications. The localized pi-pi and the charge-transfer (CT) transitions of these dications are explained and analyzed by an exciton coupling model that also considers the photophysical properties of the "monomeric" triarylamine radical cations. Together with AM1-CISD-calculated transition moments, experimental transition moments and transition energies of the bis-triarylamine dications were used to calculate electronic couplings by a generalized Mulliken-Hush (GMH) approach. These couplings are a measure for interactions of the excited mixed-valence CT states. The modification of the diabatic states reveals similarities of the GMH three-level model and the exciton coupling model. Comparison of the two models shows that the transition moment between the excited mixed-valence states mu(ab) of the dimer equals the dipole moment difference Delta of the ground and the excited bridge state of the corresponding monomer.

Quantum chemical simulation of excited states of chlorophylls, bacteriochlorophylls and their complexes

The present review describes the use of quantum chemical methods in estimation of structures and electronic transition energies of photosynthetic pigments in vacuum, in solution and imbedded in proteins. Monomeric Mg-porphyrins, chlorophylls and bacteriochlorophylls and their solvent 1:1 and 1:2 complexes were studied. Calculations were performed for Mg-porphyrin, Mg-chlorin, Mg-bacteriochlorin, mesochlorophyll a, chlorophylls a, b, c(1), c(2), c(3), d and bacteriochlorophylls a, b, c, d, e, f, g, h, plus several homologues. Geometries were optimised with PM3, PM3/CISD, PM5, ab initio HF (6-31G*/6-311G**) and density functional B3LYP (6-31G*/6-311G**) methods. Spectroscopic transition energies were calculated with ZINDO/S CIS, PM3 CIS, PM3 CISD, ab initio CIS, time-dependent HF and time-dependent B3LYP methods. Estimates for experimental transition energies were obtained from linear correlations of the calculated transition energies of 1:1 solvent complexes against experimentally recorded solution energies (scaling). According to the calculations in five-coordinated solvent complexes the magnesium atom lies out of the porphyrin plane, while in six-coordinated complexes the porphyrin is nearly planar. Charge densities on magnesium and nitrogen atoms were strongly dependent on the computational method deployed. Several dark states of low oscillator strength below the main Soret band were predicted for solvent complexes and chlorophylls and bacteriochlorophylls in protein environment. Such states, though not yet identified experimentally, might serve as intermediate states for excitation energy transfer in photosynthetic complexes. Q(y), Q(x) and Soret transition energies were found to depend on the orientation of the acetyl group and external pressure. A method to estimate site energies and dimeric interaction energies and to simulate absorption and CD spectra of photosynthetic complexes is described. Simulations for the light harvesting complexes Rhodospirillum molischianum, chlorosomes of Chlorobium tepidum and Chloroflexus aurantiacus, and LHC-II of Spinacia oleracea are presented as examples.