Molecular modeling of 3,4-pyridinedicarbonitrile dye sensitizer for solar cells using quantum chemical calculations

The geometries, electronic structures, polarizabilities, and hyperpolarizabilities of organic dye sensitizer 3,4-pyridinedicarbonitrile was studied based on Hartree–Fock (HF) and density functional theory (DFT) using the hybrid functional B3LYP. Ultraviolet–visible (UV–Vis) spectrum was investigated by time dependent DFT (TD-DFT). Features of the electronic absorption spectrum in the visible and near-UV regions were assigned based on TD-DFT calculations. The absorption bands are assigned to π → π1 transitions. Calculated results suggest that the three lowest energy excited states are due to photoinduced electron transfer processes. The interfacial electron transfer between semiconductor TiO₂ electrode and 3,4-pyridinedicarbonitrile is due to electron injection process from excited dye to the semiconductor’s conduction band. The role of cyanine in 3,4-pyridinedicarbonitrile in geometries, electronic structures, and spectral properties were analyzed.     

Theoretical Study of Fluorescence Spectra Utilizing the pKa Values of Acids in Their Excited States

Assignment of the fluorescence spectrum of firefly luciferin in aqueous solutions was achieved by utilizing not only emission energies but also theoretical absorption spectra and relative concentrations as estimated by pK_a values. Calculated Gibbs free energies were utilized to estimate pK_a values. These pK_a values were then corrected by employing the experimental results. It was previously thought that the main peak near 550 nm observed in the experimental fluorescence spectra at all pH values corresponds to emission from the first excited state of the luciferin dianion [Ando et al. (2010) Jpn. J. Appl. Phys. 49, 117002–117008]. However, we found that the peak near 550 nm at low pH corresponds to emission from the first excited state of the phenolate monoanion of luciferin. Furthermore, we found that the causes of the red fluorescence at pH 1–2 are not only the emission from phenol monoanion but also the emission from the protonated species at nitrogen atom in the thiazoline ring of dianion.     

Synthesis and evaluation of new caged compound with thiochromone derivative

A new caged firefly luciferin (luciferin) with a thiochromone S,S-dioxide (TSSDO) as a photolabile protecting group was synthesized. Photodeprotection of the caged compound proceeded smoothly under photoirradiation at 365 nm in aqueous solution. The bioluminescence of the regenerated luciferin after uncaging was detected using a typical luciferin–luciferase reaction. These results indicated that TSSDO could be an attractive chemical tool for regulating biological phenomena.     

Optical Properties of the Orchid Colored Silver(II) Fluoride Cs2AgF4

Orchid colored powder samples of Cs₂AgF₄ were prepared by a solid state reaction from CsF and AgF₂. The diffuse reflectance spectrum of a powder sample of Cs₂AgF₄ was measured in the UV/Vis region. It shows three broad bands, two in the visible‐light region at 650 nm, 500 nm and one in the UV region at 259 nm. The bands are assigned to F 2p → Ag 4d and Ag 4d → Ag 4d transitions. The optical band gap for Cs₂AgF₄ determined from the UV/Vis diffuse reflectance spectrum is approx. 2.17 eV. In order to interpret the observed absorptions, the theoretical absorption spectrum of Cs₂AgF₄ was obtained from density functional calculations.     

Separation, Identification and Determination of Luciferin in the Iranian Firefly, Lampyris turkestanicus by HPLC and Spectroscopic Methods

Abstract— Iranian firefly larvae, Lampyris turkestanicus collected from north of Iran and their luciferin were analyzed by HPLC, TLC, MS and spectroscopic Fourier transform ([FT]-IR, FT-NMR, UV and fluorescence) methods. The results showed that luciferin in L. turkestanicus lanterns was the same as in the American firefly, Photinus pyralis and synthetic D-luciferin.     

Theoretical analysis of the electronic spectrum of GeH4 from ab initio CI calculations

Ab initio CI calculations using pseudopotentials to describe germanium inner electrons are carried out on the low-lying excited singlet states (T₂) of GeH₄. A theoretical analysis of these states in terms of Mulliken population of Rydberg orbitals for each state and oscillator strengths allow us to reinterpret its experimental Vacuum UV electronic spectrum.     

Theoretical prediction of the electronic excited states and resonance Raman intensities in formamide from coupled cluster calculations

Electronic excitations and the resonance Raman spectrum of formamide were obtained from ab initio electron correlation calculations using the equation of motion coupled cluster (EOM-CCSD) method. Interpretation of the UV spectrum on the basis of calculated vertical excitation energies and oscillator strengths accounts for all experimental bands previously assigned. Our assignment, however, suggests an additional Rydberg band at about 7.4 eV which may be hidden under the main absorption. We also show that the Rydberg states appear pairwise, corresponding to n and π hole states, respectively. Using analytic derivative techniques, derivatives of the excited state energies with respect to normal coordinates of the ground state were calculated. Approximate resonance Raman intensities have been determined.     

Action spectrum and quantum yield for the photoinactivation of mnemiopsin, a bioluminescent photoprotein from the Ctenophore mnemiopsis SP.

Abstract— Ctenophores are bioluminescent marine invertebrates closely related to the coelenterates. The isolated bioluminescent systems of the ctenophores Mnemiopsis and Beroë and the hydrozoan jellyfish Aequorea are protein-luciferin complexes (photoproteins) which flash upon the addition of Ca²⁺ ions. The photoprotein mnemiopsin has an oxygen-independent quantum yield for photoinactivation of bioluminescence as high as 0.5, placing it among the most light-sensitive proteins known. We have measured the action spectrum for this photoinactivation at 107 narrow (3.4 nm) wavelength bands between 230 nm and 570 nm, covering a range of four decade units in the action. The action spectrum in the visible region is identical with the absorption spectrum of native photoprotein, implicating bound luciferin. The UV action spectrum implies that absorption by aromatic amino acid residues also leads to extremely efficient photoinactivation. Although photoinactivation is a rapid first-order reaction, destruction of the luciferin is a slower, multiple-order process. Therefore, protein-bound luciferin is not the ultimate target of the photoinactivation. Absorption of light results in the dissociation of “active oxygen” from the photoprotein. Therefore, the ctenophore photoprotein is a precharged enzyme already containing bound luciferin and oxygen.     

Solvent effects on the ultraviolet absorption spectrum of mercury atom

Absorption spectrum of mercury dissolved in hexane and heptane in the region 280–180 nm was found to consist of three bands. These bands were assigned to the ¹S₀ → ¹P₁ transition (A band, λ = 254 nm), to the ¹S₀ → ³P₂ transition (B band, λ = 226 nm) and to the ¹S₀ → ¹P₁ transition (C band, λ = 190 nm) of a mercury atom placed into a liquid cell. The B and C absorption bands of mercury in liquid solutions were observed for the first time. It was found that the A band and the C band have, respectively, distinct doublet and triplet structure, while the doublet structure of the B band is only slightly seen. The oscillator strengths of all three bands of mercury in solutions were estimated. The structure of the C, A and B bands of mercury in solutions most probably results from the removal of the degeneracy of the excited states ¹P₁, ³P₁ and ³P₂ of a mercury atom, placed into a cell of low symmetry.     

Ab initio study of electronic spectra of merocyanine 540 and its photoproducts

Molecular structures of three derivatives of merocyanine 540 (MC 540) were studied using the density functional method in conjunction with the 6‐31G*, 6‐31G**, and 6‐311G** basis sets. The excited states were calculated using the configuration interaction method involving singly excited configurations (CIS). The predicted transition energies and oscillator strength agree well with the experimental UV adsorption spectra of the studied systems. The existence of two stable conformers of merocyanine explain the experimentally observed dependence of the UV spectra upon the change of concentration of added salts. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

A comparative analysis of the UV/Vis absorption spectra of nitrobenzaldehydes

In a joint experimental and theoretical study, the UV/Vis absorption spectra of the three isomers (ortho, meta, para) of nitrobenzaldehyde (NBA) were analyzed. Absorption spectra are reported for NBA vapors, cyclohexane and acetonitrile solutions. All spectra are poor in vibronic structure and hardly affected in shape by the surroundings (vapor or solution). Moderate solvatochromic shifts of ～ -0.2 eV are measured. For all isomers vertical transition energies, oscillator strengths, and excited state dipole moments were computed using the MS-CASPT2/CASSCF and CC2 methods. Based on these calculations the experimental transitions were assigned. The spectra of all isomers are characterized by weak (ε(max) ≈ 100 M(-1) cm(-1)) transitions around 350 nm (3.6 eV), arising from nπ* absorptions starting from the lone pairs of the nitro and aldehyde moieties. The next band of intermediate intensity peaking around 300 nm (4.2 eV, ε(max) ≈ 1000 M(-1) cm(-1)) is dominated by ππ* excitations within the arene function. Finally, strong absorptions (ε(max) ≈ 10,000 M(-1) cm(-1)) were observed around 250 nm (5.0 eV) which we ascribe to ππ* excitations involving the nitro and benzene groups.     

A re-investigation of the electronic spectrum of perylene

A detailed spectroscopic analysis of the electronic absorption spectrum of the perylene molecule in boric acid glass is reported in the region 190–500 nm. To interpret the observed spectrum, the electronic energy levels and oscillator strengths have been calculated using the Free Electron Molecular Orbital (FEMO) method with limited configuration interaction [N.S. Ham and K. Ruedenberg, J. Chem. Phys. 25, 1, 13 (1956)]. The effect of solute concentration on the relative intensities of the absorption bands has also been studied. The experimentally observed transition energies of four strong bands show a linear relationship with the theoretically calculated ones. Agreement between experimental and theoretical results is good.     

Investigation of excited‐state properties of fluorene–thiophene oligomers by the SAC‐CI theoretical approach

Excited states of fluorene‐ethylenedioxythiophene (FEDOT) and fluorene‐S,S‐dioxide‐thiophene (FTSO2) monomers and dimers were studied by the symmetry‐adapted cluster (SAC)‐configuration interaction (CI) method. The absorption and emission peaks observed in the experimental spectra were theoretically assigned. The first three excited states of the optimized conformers, and the conformers of several torsional angles, were computed by SAC‐CI/D95(d). Accurate absorption spectra were simulated by taking the thermal average for the conformers of torsional angles from 0° to 90°. The conformers of torsional angles 0°, 15°, and 30° mainly contributed to the absorption spectra. The full width at half‐maximum of the FEDOT absorption band is 0.60 eV (4839 cm^?1), which agrees very well with the experimental value of 0.61 eV (4900 cm^?1). The maximum absorption wavelength is located at 303 nm, which is close to those of the experimental band (327 nm). The calculated absorption spectrum of FTSO2 showed two bands in the range of 225–450 nm. This agrees very well with the available experimental spectrum of a polymer of FTSO2, where two bands are detected. The excited‐state geometries were investigated by CIS/6‐31G(d). These showed a quinoid‐type structure which exhibited a shortening of the inter‐ring distance (0.06 Å for FEDOT and 0.04 Å for FTSO2). The calculated emission energy of FEDOT is 3.43 eV, which agrees very well with the available experimental data (3.46 eV). The fwhm_E is about 0.49 eV (3952 cm^?1), while the experimental fwhm is 0.43 eV (3500 cm^?1). For FTSO2, two bands were also found in the emission spectrum. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010     

Purification and partial spectral characterization of a novel luciferin from the luminous enchytraeid Fridericia heliota

A homogeneous luciferin preparation has been obtained from the luminous soil enchytraeid Fridericia heliota, which has an ATP-dependent luminescent system. A procedure for luciferin purification without losing fractions of active luciferase has been developed. The luciferin specific activity is 4000 times increased; its UV absorption spectrum maximum is 294 nm with a local minimum at 262 nm. The luciferin of the enchytraeid F. heliota is significantly different from firefly luciferin, whose luminescent reaction also requires ATP, and it also appears to have no similarities to other known luciferins.     

Phytochemical fabrication and characterization of silver nanoparticles by using Pepper leaf broth

The Pepper leaves extract acts as a reducing and capping agent in the formation of silver nanoparticles. A UV–Vis spectrum of the aqueous medium containing silver nanoparticles demonstrated a peak at 458 nm corresponding to the plasmon absorbance of rapidly synthesized silver nanoparticles that was characterized by UV–Vis spectrophotometer. The morphology and size of the benign silver nanoparticles were carried out by the transmission electron microscope (TEM) and field emission scanning electron microscope (FE-SEM). The sizes of the synthesized silver nanoparticles were found to be in the range of 5–60 nm. The structural characteristics of biomolecules hosted silver nanoparticles were studied by X-ray diffraction. The chemical composition of elements present in the solution was determined by energy dispersive spectrum. The FTIR analysis of the nanoparticles indicated the presence of proteins, which may be acting as capping agents around the nanoparticles. This study reports that synthesis is useful to avoid toxic chemicals with adverse effects in medical applications rather than physical and chemical methods.     

Spectroscopic evidence for a dinitrogen complex of gallium and estimation of the Ga-N2 bond strength

Matrix-isolation experiments were performed to study the interaction between Ga atoms and N2 by using Raman and UV/Vis spectroscopies for detection and analysis. It was revealed that a weak complex is formed, for which resonance Raman spectra were obtained. Several overtones were sighted, allowing a rough estimate of the Ga-N2 fragmentation energy to be made (approximately 19 kJ mol(-1)). The excitation profile obtained from the spectra at different laser wavelengths agrees with the UV/Vis spectrum and shows that the complex exhibits an electronic transition at around 410 nm. At the Ga atom, this transition can be described as a 2S<--2P or 2D<--2P excitation, which is red-shifted from its position for free Ga atoms (approximately 340 nm and 270 nm for 2S<--2P and 2D<--2P, respectively) as a result of N2 complexation. The effect of complexation involves, therefore, only slight stabilization of the 2P ground state but relatively strong stabilization of the excited (2)S state. Accordingly, for the Ga atom in its excited 2S state, the Ga-N2 bond energy can be estimated to be around 79 kJ mol(-1).     

Electronic spectra of nitroethylene

A systematic study of the electronic excited states of nitroethylene (C₂H₃NO₂) was carried out using the approximate coupled‐cluster singles‐and‐doubles approach with the resolution of the identity (RI‐CC2), the time dependent density functional theory with the CAMB3LYP functional (TDDFT/CAMB3LYP) and the DFT multireference configuration interaction (DFT/MRCI) method. Vertical transition energies and optical oscillator strengths were computed for a maximum of 20 singlet transitions. Semiclassical simulations of the ultraviolet (UV) spectra were performed at the RI‐CC2 and DFT/MRCI levels. The main features in the UV spectrum were assigned to a weak n‐π* transition, and two higher energy π_CC+O‐π* bands. These characteristics are common to molecules containing NO₂ groups. Simulated spectra are in good agreement with the experimental spectrum. The energy of the bands in the DFT/MRCI simulation agrees quite well with the experiment, although it overestimates the band intensities. RI‐CC2 produced intensities comparable to the experiment, but the bands were blue shifted. A strong π_CC+O‐π* band, not previously measured, was found in the 8–9 eV range. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Ultraviolet absorption and vibrational spectra of 2-fluoro-5-bromopyridine

The ultraviolet absorption spectrum in the range 340-185 nm in the vapour and solution phase has been measured for 2-fluoro-5-bromopyridine. Three fairly intense band systems identified as the pi* <-- pi transitions II, III and IV have been observed. A detailed vibronic analysis of the vapor and solution spectra is presented. The first system of bands is resolved into about sixty-two distinct vibronic bands in the vapour-phase spectrum. The 0,0 band is located at 35944 cm(-1). Two well-developed progressions, in which the excited state frequencies nu'25 (283 cm(-1)) and nu'19 (550 cm(-1)) are excited by several quanta, have been observed. The corresponding excited state vibrational and anharmonicity constants are found to be omega'i = 292 cm(-1), x'ii = 4.5 cm(-1) (i = 25) and omega'i = 563.8 cm(-1), x'ii = 6.9 cm(-1) (i = 19). The other two band systems show no vibronic structure, the band maxima being located at 48346 and 52701 cm(-1), respectively. The oscillator strength of the band systems in different solutions and the excited state dipole moments associated with the first two transitions have been determined by the solvent-shift method. The infrared spectrum in the region 4000-130 cm(-1) and the laser Raman spectrum of the molecule in the liquid state have been measured and a complete vibrational assignment of the observed frequencies is given. A correlation of the ground and excited state fundamental frequencies observed in the UV absorption spectrum with the Raman or infrared frequencies is presented.     

PHOTODYNAMIC EFFECTS INDUCED BY THE LUCIFERIN/LUCIFERASE SYSTEM

Abstract— Luciferin from Photinur pyralis is an effective sensitizer, when excited with UV light in the range of 310–390 nm. With histidine or dithiothreitol as substrate, a type II photooxidation occurs, as judged from the inhibitory effect of sodium azide. During the ATP-driven luciferin-luciferase reaction, the resulting bioluminescence does not induce photodynamic reactions, as there is no overlap between the bioluminescence spectrum and the excitation spectrum of luciferin. However, in the presence of a second sensitizer, excitable by the bioluminescent light, photodynamic reactions can take place in the absence of exogenous light. As a consequence several photosensitizers can thus provoke photodynamic inactivation of luciferase.     

Electronic spectra and transitions of the fullerene C60

Absorption spectra of C₆₀ have been measured in the ranges (a) 190–700 nm in n-hexane solutions at 300 K, (b) 390–700 nm in n-hexane and in 3-methylpentane solutions at 77 K. 40 vibronic bands were observed. They exhibit a large range of bandwidths and intensities, whose significance is discussed. Assignment of electronic transitions has been carried out using the results of theoretical calculations. Vibronic structures have been analyzed within the framework of theories of electronic transitions of polyatomic molecules applied to the I_h symmetry group. Nine allowed ¹T_1u−¹A_g transitions have been assigned in the 190–410 nm region. Observed and calculated allowed transition energies and oscillator strengths are compared. Detailed vibronic analyses of the 1 ¹T_1u−1 ¹A_g and 2 ¹T_1u−1 ¹A_g transitions illustrate the role of Jahn-Teller couplings. Orbitally forbidden singlet-singlet transitions are observed between 410 and 620 nm. Their vibronic structures were analyzed in terms of concurrent Herzberg-Teller and Jahn-Teller vibronic interactions. The 77 K spectra provided useful information on hot bands and on other aspects of the analyses. Vibronic bands belonging to triplet←singlet transitions were detected between 620 and 700 nm.