Electronic Absorption Properties Research Articles

Theoretical assessment of TD-DFT applied to a ferrocene-based complex

We present a theoretical study of the electronic absorption spectrum of the 2-ferrocenyl-1,8-naphthyridine (FcNP) complex using the time-dependent density functional theory (TD-DFT) approach. The calculations were carried out at the DFT/LANL2DZ(Fe)/6-31++G(d) level of theory with nine DFT functionals of the type GGA (PBE, B97D), HGGA (B3LYP, PBE0), HMGGA (M05, M06) and range-separated (wB97XD, CAM-B3LYP, LC-wPBE) in the condensed phase (CH2Cl2). The experimental spectrum for FcNP presents three electronic absorption bands (A, B, C) in the UV region and one band (D) in the visible region. We found that there is no unique functional that reproduces the entire electronic spectrum. GGA and LC-wPBE functionals predict large errors (up to 0.57eV) for the UV bands. On the contrary, HGGA (PBE0), HMGGA (M05, M06) and range-separated (wB97XD, CAM-B3LYP) functionals give small errors for these bands, 0.18, 0.12 and 0.25eV, respectively. Band D is well described by all the functionals with errors up to 0.26eV, except by the M05 and M06 functionals, which fail in this region with significant errors (0.52 and 0.56eV). The analysis of the excitation energies shows that the PBE0, wB97XD and CAM-B3LYP functionals predict the best agreement with the experimental data. The two stronger bands (A, B) in the UV region are assigned to a ligand–ligand charge transfer (L-LCT) that involves the cyclopentadienyl rings (Cp) and the naphthyridine fragment (NP), and then associated with π→π∗ electronic transitions. The two weaker bands (C, D) are assigned to a charge transfer from ligand (Cp) to metal (Fe)-ligand (NP) (L-MLCT) which is mainly addressed through the dxy and dz2 atomic orbitals, respectively. No charge transfer is observed between metal and NP ligand. It was shown that the theoretical methods used for understanding the electronic absorption properties of FcNP were adequate because the results showed an excellent agreement with experimental ones.

Novel derivatives of regioisomerically pure 1,7-disubstituted perylene diimide dyes bearing phenoxy and pyrrolidinyl substituents: Synthesis, photophysical, thermal, and structural properties

Two new isomerically pure 1,7-substituted perylene-bisimide derivatives namely; 1,7-Di(4-tert-butylphenoxy)-N,N′-bis[2-(diethylamino)ethyl]-3,4,9,10-perylene-tetracarboxylic diimide (6) and 1,7-Di(pyrrolidinyl)-N,N′-bis[2-(diethylamino)ethyl]-3,4,9,10-perylene- tetracarboxylic diimide (7), have been synthesized and their electronic absorption, steady-state fluorescence, and thermal properties were studied. Both compounds show good solubility in a range of organic solvents. Attachment of two electron donating tert-butyl-phenoxy groups at the 1,7-positions in (6) resulted in a red shifted absorption band with absorption maximum at 543nm. UV–visible absorption spectrum of (7) shows a broad absorption band within the red region. Absorption maximum of lowest energy transition now shifts to 704nm. Both compounds (6) and (7) exhibit low fluorescence quantum yields of 0.133 and 0.007, respectively. Density functional theory (DFT) calculations revealed that the attachment of electron donating groups at 1,7-positions of PDIs, results in an increase in frontier orbitals energy levels. Observed energy increase in HOMO is larger in each case, compared to the energy increase in LUMO levels. Calculated band gaps for (6) and (7) are 2.462 and 2.128eV respectively.

Light absorption and photoluminescence due to interfacial charge-transfer transitions in aromatic amine-functionalized silicon nanoparticles

Aromatic amine-functionalization of silicon nanoparticles induces a new absorption band in the near UV-to-blue region and efficient blue photoluminescence even at room temperature. However, the origin of the absorption band and photoluminescence has not yet been understood well. Here, we study theoretically the electronic structure and light absorption and photoluminescence properties of carbazole-functionalized silicon nanoparticles. We reveal that the absorption band and photoluminescence are attributed to interfacial charge-transfer (ICT) transitions between the covalently-boned carbazole and silicon nanoparticles. The ICT transitions are induced by strong electronic couplings between CA and a silicon nanoparticle via the SiN bond.

A New Potent Inhibitor of Glycogen Phosphorylase Reveals the Basicity of the Catalytic Site.

The design and synthesis of a glucose-based acridone derivative (GLAC), a potent inhibitor of glycogen phosphorylase (GP) are described. GLAC is the first inhibitor of glycogen phosphorylase, the electronic absorption properties of which are clearly distinguishable from those of the enzyme. This allows probing subtle interactions in the catalytic site. The GLAC absorption spectra, associated with X-ray crystallography and quantum chemistry calculations, reveal that part of the catalytic site of GP behaves as a highly basic environment in which GLAC exists as a bis-anion. This is explained by water-bridged hydrogen-bonding interactions with specific catalytic site residues.

Visible absorbing croconium dyes with intramolecular hydrogen bonding: A combined experimental and computational study

Croconium molecules CR1-CR4 with break-in conjugation (CN Bonding) was synthesized by condensation of croconic acid and arylamines. By using combined experimental and theoretical methods like UV–visible spectra, DFT and TDDFT studies, we have characterized electronic absorption properties. The reported molecules are having absorption in visible region ranging from 450 to 550 nm with large extinction coefficient (2.5–5.0 × 104 M−1 cm−1). We find that CR2 and CR4 are showing 50 to 100 nm red shifted absorption than CR1 and CR3. This red shift is possibly due to presence of intramolecular hydrogen bonding in CR2 and CR4. Further this is supported by DFT studies, in case of CR2 and CR4 shows strong intramolecular hydrogen bonding between oxygen of carboxylate group (at ortho position of phenyl ring) and hydrogen of nitrogen attached to the central croconate ring. It is also observed that, there is small diradicaloid character in these molecules. This study is helpful in design and synthesis of new croconium dyes which are useful in materials applications.

Structural and Optical Properties of New Naphthalene and Perylene Imide Imidazoles

ABSTRACTNew unsymmetrically substituted naphthalene and perylene imide imidazoles, N-(2-ethylhexyl)-naphthalene-3,4-(4,5-dicyano-1,2-benzimidazole)-9,10-dicarboxyimide and N-(1-heptyloctyl)-perilene-3,4-(4,5-dicyano-1,2-benzimid-azole)-9,10-dicarboxyimide, were synthesized via condensation reactions of diaminophthalonitrile and aromatic monoimide monoanhydride derivatives. Their structural analyses have been conducted by using general spectroscopic methods including FT-IR, 1H- and 13C-NMR, mass and elemental analysis. The molecular structure of naphthalene derivative was also determined by single crystal x-ray diffraction. Electronic absorption and emission properties were investigated on comparison. For studied compounds, both DFT and TDDFT calculations were carried out with the 6-311G(d,p) basis set, taking into account solvation effects by means of polarizable continuum model as implemented in the Gaussian 09 package.

A new phosphorescent heteroleptic cuprous complex with a neutral 2-methylquinolin-8-ol ligand: synthesis, structure characterization, properties and TD-DFT calculations.

Luminescent CuI complexes have emerged as promising substitutes for phosphorescent emitters based on Ir, Pt and Os due to their abundance and low cost. The title heteroleptic cuprous complex, [9,9-dimethyl-4,5-bis(diphenylphosphanyl)-9H-xanthene-κ2P,P](2-methylquinolin-8-ol-κ2N,O)copper(I) hexafluorophosphate, [Cu(C10H9NO)(C39H32OP2)]PF6, conventionally abbreviated as [Cu(Xantphos)(8-HOXQ)]PF6, where Xantphos is the chelating diphosphine ligand 9,9-dimethyl-4,5-bis(diphenylphosphanyl)-9H-xanthene and 8-HOXQ is the N,O-chelating ligand 2-methylquinolin-8-ol that remains protonated at the hydroxy O atom, is described. In this complex, the asymmetric unit consists of a hexafluorophosphate anion and a whole mononuclear cation, where the CuI atom is coordinated by two P atoms from the Xantphos ligand and by the N and O atoms from the 8-HOXQ ligand, giving rise to a tetrahedral CuP2NO coordination geometry. The electronic absorption and photoluminescence properties of this complex have been studied on as-synthesized samples, whose purity had been determined by powder X-ray diffraction. In the detailed TD-DFT (time-dependent density functional theory) studies, the yellow emission appears to be derived from the inter-ligand charge transfer and metal-to-ligand charge transfer (M+L')→LCT excited state (LCT is ligand charge transfer).

PH value-dependent electronic absorption and Ru(III/II) potential of bis-tridentate pincer ruthenium complexes

Two bis-tridentate pincer complexes [Ru(H2bip)(Mebib)](PF6)2 (1(PF6)2) and [Ru(H2bip)(H2bib)](PF6)2 (2(PF6)2) were prepared and studied, where H2bip is 2,6-bis(benzimidazol-2-yl)pyridine, Mebib is the 2-deprotonated 1,3-bis(N-methylbenzimidazol-2-yl)benzene, and H2bib is 2-deprotonated 1,3-bis(benzimidazol-2-yl)benzene. These complexes were isolated as cyclometalated Ru(III) salts with a [(NCN)(NNN)] coordination due to a low Ru(III/II) redox potential. Complex 1(PF6)2 has two N−H protons on the NNN ligand side, while complex 2(PF6)2 has four N−H protons. Absorption spectral analysis showed that two deprotonation steps were distinguished for 1(PF6)2 with pKa1 and pKa2 of 3.46 and 5.88, respectively. In comparison, four deprotonation steps were observed for 2(PF6)2 with four pKa values of 3.45, 5.95, 8.95, and 10.98, respectively. When the solution was changed from acidic to basic, the Ru(III/II) redox wave of 1(PF6)2 and 2(PF6)2 shifted from +0.20 V vs Ag/AgCl to a less positive region by 540 and 850 mV, respectively. These studies suggest that the electronic absorption and electrochemical properties of these complexes are very sensitive to pH effect.

Synthesis and antimicrobial evaluation of some new hydrazo, dihydropyridazinyl and triazolyl derivatives containing indole nucleus

PurposeThe aim of this paper is synthesis of some new hydrazo, dihydropyridazinyl and triazolyl derivatives containing indole nucleus and their antimicrobial evaluation.Design/methodology/approachTreatment of 3-(1H-indol-3-yl)-3-oxopropanenitrile (1) with different aryl diazonium salts 2a-j gave the corresponding arylazohydrazone derivatives 3a-j. The azo derivatives 3d and 3e were used as the key intermediate for the synthesis of some new diazines 5d, e and triazoles 7d, e. The newly synthesized compounds were characterized by electronic absorption properties – IR, 1HNMR and MS studies – and screened for their biological evaluation. Compounds 3a-j, 5d, e and 7d, e showed promising results as antimicrobial agents.FindingsCompounds 3a-j, 5d, e and 7d, e showed promising results as antimicrobial agents.Originality/valueNo details regarding the synthesis of such dyes are reported before in the literature.

Photoreactivity, Optical Behavior and DFT Studies of 2,5-Bis[4-choloro-acetyl(thiophen-2-ylmethylene)]cyclopentanone BCTCP in Different Solvents.

Diarylidenecyclopentanone compound namely, 2,5-bis[4-choloroacetyl-(thiophen-2-ylmethylene)]cyclopentanone (BCTCP) was firstly synthesized using the normal condition of Friedel-Crafts method by reacting 2,5-bis(thiophen-2-ylmethylene)cyclopentanone (BTCP) with chloroacetyl chloride in the presence of aluminum chloride anhydrous. The structure of this compound was confirmed by elemental and spectral analyses including FT-IR, 1H-NMR, 13C-NMR and mass spectrometry. The electronic absorption and emission properties of BCTCP were studied in different solvents. BCTCP displays a slight solvatochromic effect of the absorption and emission spectrum, indicating a small change in dipole moment of BCTCP upon excitation. BCTCP displayed photodecomposition in chlorinated solvents upon irradiating with 365nm light. Ground and excited states electronic geometric optimizations were performed using density functional theory (DFT) and time-dependent density functional theory (TD-DFT), respectively. A DFT natural bond orbital (NBO) analysis complemented the intramolecular charge transfer (ICT). The simulated maximum absorption and emission wavelengths are in line the observed ones in trend, and were proportionally red-shifted with the increase of the solvent polarity. The stability, hardness and electrophilicity of BCTCP in different solvents were correlated with the polarity of the elected solvents.

Theoretical study on the electronic structures and spectral properties of two series of osmium(II) complexes with different substituent groups

ABSTRACTTwo series of osmium(II) complexes with different substituent groups (-CF3, -N(CH3)2) have been studied by using the density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods, to investigate their electronic structures, absorption, and emission properties. The influence of different substituted groups on their photophysical properties has also been explored. The lowest energy absorption and emission wavelengths calculated are in good agreement with the available experimental values. Besides, ionization potential (IP), electron affinities (EA), and reorganization energy (λ) were calculated to evaluate the charge transfer and balance properties between hole and electron. It is expected that the theoretical studies could provide valuable information for the phosphorescent osmium(II) material for use in the organic light-emitting diodes.

Conformational, spectroscopic and nonlinear optical investigations on 1-(4-chlorophenyl)-3-(4-chlorophenyl)-2-propen-1-one: a DFT study

The density functional theory calculations on 1-(4-chlorophenyl)-3-(4-chlorophenyl)-2-propen-1-one (CPCPP) are performed by using B3LYP and HSEh1PBE levels. These methods along with 6-311++G(d,p) basis set have been used to determine optimized molecular geometries, vibrational frequencies, electronic absorption wavelengths and bonding features of CPCPP. The solvent effect on the electronic absorption properties of CPCPP is examined at polar (ethanol and water) and nonpolar (toluene and n-hexane) solvents. In order to find the most stable conformers, conformational analysis is carried out by using B3LYP level. The computed small energy gaps between HOMO and LUMO energies show that the charge transfers occur within CPCPP. DFT calculations have been also performed to investigate the dipole moment (μ), mean polarizability (α), anisotropy of polarizability (Δα), first order static hyperpolarizability (β) for CPCPP. The obtained values show that CPCPP is an excellent candidate to nonlinear optical materials. NBO analysis has been used to investigate the bond strengths, molecular stability, hyperconjugative interactions and intramolecular charge transfer (ICT).

Fluorescence properties of p-tert-butyldihomooxacalix[4]arene derivatives and the effect of anion complexation

The intrinsic electronic absorption and fluorescence properties of several dihomooxacalix[4]arenes are studied.

Electronic structure and optical absorption properties of -AgVO3 with vacancy defects

Semiconductor photocatalysts have received much attention due to their applications of wastewater treatment and air purification. The monoclinic -AgVO3, which has narrow band gap (2.11 eV) and can respond to visible light, has been considered as one of the promising semiconductor photocatalysts. The vacancy defects always exist in -AgVO3 prepared under the conventional synthesis conditions and have important influences on the structure and properties of -AgVO3. Systematic theoretical study of the vacancy defects in -AgVO3 is still lacking. In this paper, using density functional theory plus U (DFT+U) approach, the Ag vacancy, O vacancy and Ag-O bivacancy in -AgVO3 are studied. The formation energy, band structure, differential charge density and optical absorption spectrum of -AgVO3 with vacancy defects are carefully investigated. When the U values are chosen as 6 eV and 2.7 eV for the Ag-4d and V-3d electrons respectively, the reasonable lattice parameters and band gap value can be obtained for -AgVO3. By comparing the formation energies of different Ag and O vacancies, we find that the dominating vacancy defects in -AgVO3 are Ag3 and O1 vacancies, and the formation of Ag vacancy is much easier than that of O vacancy. The analyses of the total and partial density of states indicate that the conduction band arises mainly from V-3d orbit, and the valence band is mainly composed of Ag-4d and O-2p states for -AgVO3. With Ag3 vacancy, O1 vacancy or Ag3-O1 bivacancy, the band gaps of -AgVO3 all decrease in different degrees. The Ag3 vacancy behaves as p-type donor, allowing the Fermi level to shift down to the valence band maximum. However, O1 vacancy and Ag3-O1 bivacancy both act as n-type donors, and the Fermi level shifts to the conduction band minimum. The change of the Fermi level for the vacancy defect systems also means that the charge transfer occurs among the atoms around the vacancy, which is analyzed by calculating the differential charge density. The Ag3 vacancy and O1 vacancy have little effects on the light absorption of -AgVO3 in the range of visible light, while O1 vacancy and Ag3-O1 bivacancy in -AgVO3 cause the obvious absorption of light in the near infrared region.

First principle study of electronic structures and optical absorption properties of O and S doped graphite phase carbon nitride (g-C3N4)6 quantum dots

Graphite phase carbon nitride (g-C3N4) quantum dots have received much attention due to its good stability, water solubility, biological compatibility, non-toxicity as well as strong fluorescence characteristics. In order to enhance the light absorption and improve photocatalytic activities of the g-C3N4 quantum dots, theoretical studies are carried out on the O and S atoms doped (g-C3N4)6 quantum dots. First-principles calculations based on the density functional theory and time dependent density functional theory are performed to investigate the geometries, electronic structures and ultraviolet visible absorption spectra of O and S atoms doped (g-C3N4)6 quantum dots. The results show that the highest electron occupied molecular orbital-the lowest electron unoccupied molecular orbital (HOMO-LUMO) energy gap of doped (g-C3N4)6 quantum dots is significantly reduced though the CN bond lengths closely related to the impurities only change slightly. The calculated formation energies indicate that the O-doped (g-C3N4)6 quantum dots are more stable, and the O atom tends to substitute for N atom at the N3-site, while the S atoms prefer to substitute for N atom at the N8-site. The simulated spectra indicate that the doping of O and S in (g-C3N4)6 could improve the light absorption. Not only the absorption peaks are extended from the UV to the infrared region (e.g. 200-1600 nm), but also the corresponding absorption intensities are enhanced significantly by doping the O or S atoms with the appropriate concentration. The increase of proper impurity concentration will lead to a pronounced red shift in light absorption. The effect of doping site on the optical absorption property of (g-C3N4)6 quantum dots shows that the absorption intensity is mainly affected in the visible range, however, besides the influence on the absorption intensity, the light absorptions of some structures are also affected beyond 800 nm. Overall, the O atoms and S atoms have a substantially similar effect on the light absorption of the (g-C3N4)6 quantum dots, while the effects of these impurity atoms are different in the long wavelength region. Oxygen doping is better than sulfur doping in the absorption of (g-C3N4)6 quantum dots by comparing the doping of O and S. These first-principles studies give us a method to effectively improve the light absorption of g-C3N4 quantum dots, and could provide a theoretical reference for tuning its electronic optical properties and applications.

Pure aromatic hydrocarbons with meta-linked phenyl-core and perihedral fluorene substitutions with/without inert groups of tert-butyl: bipolar hosts for blue phosphorescence

Two pure hydrocarbon molecules of 1,3,5-tris(9-phenyl-9H-fluoren-9-yl)benzene (m TPFB) and 1,3,5-tris(2-tert-butyl-9-phenyl-9H-fluoren-9-yl)benzene (t Bu-m TPFB) were synthesized. Due to the conjugation blocked connection mode and rigid/bulky substitutions, these two materials possess high triplet energy, enabling them as good hosts for blue phosphor in PhOLEDs. By studying their thermal, electrochemical, electronic absorption and photoluminescent properties, it was found that the influence of the inert tert-butyl group on material photoelectrical properties is negligible. For instance, m TPFB and t Bu-m TPFB showed very similar absorption and emission profiles, with almost the same bandgap, triplet energy and energy levels. However, the encapsulation of tert-butyl on the 2-position of 9-phenylfluorene enhanced material thermal stability. Most importantly, carrier transport properties were improved dramatically, as proved by the mono carrier device. Blue phosphorescent OLEDs hosted by t Bu-m TPFB showed external quantum efficiency of 15.2% and current efficiency of 23.0 cd/A, which were much higher than that of the OLEDs based on m TPFB with the analogous structure.

Electronic and optical properties of B- and/or In-doped GaAs calculated using many-body Green’s Function theory

Using ab initio many-body Green’s Function theory, the electronic and optical properties of pure BAs, InAs as well as B- and/or In-doped GaAs supercells were studied. The results show that the calculated quasiparticle band gaps of BAs and InAs are in agreement with the experiments. The electronic and optical absorption properties of B- and/or In-doped GaAs are very sensitive to the lattice constant models used in the calculations, which can explain the controversies in previous theoretical and experimental works. Under the lattice constant condition based on the Vegard’s Law, the reduced band gap and the redshift of the first excited state E 0 can be observed for In y Ga1–y As with In concentrations(atomic fractions) ranging from 0 to 15.625%, while the band gap increase and the blueshift of state E 0 can be realized for B x Ga1–x As. However, an opposite trend can be found when the lattice constant is fixed to the experimental value, i.e., In doping leads to a band gap increase and a blueshift of the E 0 state, while B doping results in a band gap decrease and a redshift of the E 0 state. For B x Ga1–x–y InyAs, the values of the band gap variation and the shift of state E 0 are well located between the B and In mono-doping cases. It is worth mentioning that B doping does not introduce new impurity states in the band gap of GaAs or In y Ga1–y As.

The pH Dependent Protein Structure Transitions and Related Spin-State Transition of Cytochrome c′ from Alcaligenes xylosoxidans NCIMB 11015

Abstract The unusual magnetic/spectroscopic properties of Cytochrome c′ (Cyt c′) have been discussed, especially concerning the possibility of a quantum mechanically mixed-spin configuration of heme Fe(III). Here, four unique-spin species were identified from the magnetic circular dichroism (MCD) spectra of Cyt c′ from Alcaligenes xylosoxidans (AxCyt c′). The electrospray ionization mass spectrometric (ESI-MS) and circular dichroism (CD) spectroscopic data showed the overall conformation of AxCyt c′ was unchanged, in complete contrast to the drastic changes in the heme MCD spectra over the range of pH 3.5 and 11.8. The pH dependency of ESI-MS, electronic absorption, MCD, and CD spectroscopic properties of AxCyt c′ enabled us to reveal the undiscovered correlation between the protein-folding state and the electronic structure of the active site as a function of pH. The mechanism of alkaline spin-state transition through the rearrangement of the hydrogen-bonding linkage between Helix C and D is also proposed on the basis of atomic resolution crystal structure analyses (A. Takashina, M. Unno, T. Kohzuma, Chem. Lett. 2015, 44, 268).

Electronic and optical absorption properties of the derivatives of 1,3,4-Oxadiazole

Abstract The present data article report the electronic and optical properties such as ionization energy (IE), electron affinity (EA), energy gap between highest occupied and lowest unoccupied molecular orbitals (ΔEHOMO-LUMO) and maximum absorption wavelength (λmax) for mono- and disubstituted derivatives of 1,3,4-oxadiazole with electron-donating and -withdrawing substituents. For the mono substituted derivatives studied, the pyrrole substituted oxadiazole has the least value of ionization energy and nitro substituted oxadiazole has the highest value of electron affinity. Among the various disubstituted derivatives of oxadiazole, the one with the substitution of pyrrole as a donor moiety and nitro as an acceptor moiety showed remarkable optical properties suggesting their use in opto-electronic devices.

Design and synthesis of BODIPY sensitizers with long alkyl chains tethered to N-carbazole and their application for dye sensitized solar cells

In this study, three boron dipyrromethenes (BODIPY) dyes with extended conjugation and electron donating carbazole groups with different alkyl chain lengths tethered to N-carbazole were synthesized and characterized for dye-sensitized solar cells. The goal was to study the effect of different alkyl chain lengths on dye aggregation at TiO2 surface. The proposed molecular strategy resulted in BODIPY dyes which showed interesting electronic absorption and fluorescence properties. It was observed that intramolecular energy transfer decreases with the increase in alkyl chain length possibly due to induced changes in molecular geometry caused by long alkyl chains. Additionally, interface analysis by impedance spectroscopy in comparison to N719 sensitized TiO2 solar cell showed significant charge transport related losses (Nyquist plot) most likely due to impedance resulted from aggregated BODIPY dye on TiO2 surface. Femtosecond transient absorption studies showed the loss of excited electrons by recombination with oxidized ground state of the sensitizers.