Visible to NIR absorbing C–N and C–C bonding squaraines: A computational study

We report a comparative computational study of 2 series of molecules with C–N bonding squaraines (NSQ) and C–C bonding squaraines (CSQ), having absorption from visible to near infrared region (350‐800 nm). The NSQ are considered as molecules with break‐in conjugation, and CSQ are considered as molecules with complete conjugation in molecular backbone. The lowest electronic excitations in CSQ molecules are always having around 200 nm red shifted absorption than its corresponding NSQ molecules. The reason for this drastic red shift in CSQ series than NSQ has been systematically studied by density functional theory, time‐dependent density functional theory, and symmetry adopted cluster configuration interaction methods. The CSQ series are showing less charge transfer than NSQ, but having small diradical character. This study may be helpful in design and synthesis of new squaraine dyes, which are useful in materials applications.     

TDDFT Investigation of the Electronic Structures and Photophysical Properties of Fluorescent Extended Styryl Push-Pull Chromophores Containing Carbazole Unit

Push-pull chromophores attached to carbazole based π-conjugating spacers bearing N-alkylamino donors, cyanovinyl and carbethoxy acceptors have been studied by the means of UV-Visible measurements. The intramolecular charge transfer (ICT) of these π-conjugated systems has also been tested by investigating the ability of the solute molecules to undergo shifts in their fluorescence emission maxima with increasing solvent polarity. Density Functional Theory [B3LYP/6-31G(d)] and Time Dependent Density Functional Theory [TD-B3LYP/6-31G(d)] computations have been used to have more understanding of the structural, molecular, electronic and photophysical parameters of push-pull dyes. The largest wavelength difference between the experimental and computed electronic absorption maxima was 45 nm. For emission, a largest difference of 61 nm was observed. The ground state and excited state dipole moments in different solvents were determined using experimental solvatochromic data and computed Onsager radii. The dipole moments of the molecules in the excited state were observed to be higher than in the ground state.     

Understanding the absorption and emission spectra of borondipyrromethene dye and its substituted analogues

Borondipyrromethene (BODIPY) dye possesses a bright and long wavelength emitting fluorescent character with a wide spectral range from visible to near infrared region. In the present work, the spectral properties of BODIPY dyes were analyzed using ab intio and density functional theory methods. The ground and excited state geometries of BODIPY and its substituted analogues in chloroform medium, were optimized using the density functional theory (DFT) and singly excited configuration interaction (CIS) methods. Based on the ground and excited state geometries, the absorption and emission spectra have been calculated using time-dependent density functional theory (TDDFT) method. The TDDFT calculations have been performed using hybrid exchange correlation functionals B3LYP and M06-HF and long-range separated functionals LC-BLYP, LC-BOP, LC-PBE, LC-PBE0 and CAM-B3LYP. The solvent phase calculations were carried out using polarizable continuum model (PCM). The TDDFT investigation reveals that the substitution of acceptor, donor–donor, donor–acceptor–donor and phenyl group in BODIPY dye influence the absorption and emission spectra significantly.     

On the nature of some biradicaloid and antiaromatic Vis/NIR‐chromophores

Dyes derived from the biradicalic oxyallyl and cyclopentadienylium were calculated by time‐dependent density functional theory (TDDFT) and the characteristics of the prominent low‐energy transitions revealed by graphical means. According to theoretical and experimental studies, 4‐aminophenyl‐substituted dyes absorb intensely at long wavelengths up to the near infrared. If the amino groups are removed the absorption wavelengths are changed little. As found in the previous studies on the squaraine and croconaine oxyallyl dyes, the substituents play only a minor role in the spectral excitation. Charge‐transfer‐type excitations do not occur between the donor aryl substituents and the central oxyallyl or cyclopentadienylium acceptor group. This behaviour is exceptional since donor–acceptor compounds tend to produce charge‐transfer‐ or polymethine‐type electronic transitions. The hitherto rarely used electron density difference (EDD) maps clearly unveiled the spectral excitation features. The spectral excitation of the title compounds is predominantly localized at the oxyallyl and cyclopentadienylium groups, respectively. Characteristics of simple chromophoric compounds and of conventional CT‐ and polymethine dyes are given for comparison. The biradicaloid character of these dyes is supported by the calculated low singlet–triplet splitting energies. Spin properties were characterized in terms of expectation values of the S²‐operator and antiaromatic properties in terms of nucleus‐independent chemical shifts (NICS). According to the ΔE_S/T and <S²> criteria compounds with the acyclic oxyallyl fragment are more biradicaloid. The parent compounds oxyallyl, thioxyallyl and cyclopentadienylium, display extremely large <S²> values. These compounds are triplets in the ground state. The absorption wavelengths of selected biradicaloid species were also calculated by the multi‐reference SORCI method. Copyright © 2010 John Wiley & Sons, Ltd.     

NLO characteristics of D-π-A coumarin-thiophene bridged azo dyes by Z-scan and DFT methods

ABSTRACT

The structural, electronic, intramolecular charge transfer (ICT) and nonlinear optical (NLO) properties of the donor-π-acceptor (D-π-A) azo linked dyes bearing coumarin thiophene bridge with different acceptors were inspected by Z-scan and DFT methods. The dye 3a exhibits bathochromic absorption maxima (649 and 650?nm) in the near IR region in DMF and DMSO. The dye 3a holds low HOMO–LUMO gap elucidated by CV and DFT indicating strong ICT character. The thermal stability is high for 3a and it shows enhanced NLO property by Z-scan and DFT methods as predicted in both global and range-separated hybrid functionals. The molecular geometry was optimised using B3LYP/6-311?+?g(d,p). The ICT characteristics are correlated with NLO properties obtained by Z-scan and DFT techniques.     

Visible absorbing symmetrical squaraine and croconine dye derivatives: A comparative computational study

Visible absorbing C–N bonding squaraines (SQ1‐SQ5) and croconines (CR1‐CR5) with an increase in conjugation at donor groups and heteroaromatic donor substituents have been studied by density functional theory and time‐dependent density functional theory methodologies. In these molecules, croconines always have absorption nearly 100‐nm red shift than its corresponding squaraines (it is in consistent with C–C bonding, near infrared absorbing squaraine and croconines). The reason behind this drastic red shift, by changing the central acceptor of 4‐membered squarate ring with 5‐membered croconate ring, has been analyzed by considering the concept of diradical character and variation in central C–C–C angle. It is also observed that within the same series of molecules (either in squaraine or in croconines), with an increase in donor capacity (conjugation), absorption increases towards longer wavelength region because of destabilization of HOMO and stabilization of LUMO levels. A small blue shift was observed for heteroaromatic donor groups when compared with aromatic donor group.     

Portuguese 16th century tiles from Santo António da Charneca's kiln: a spectroscopic characterization of pigments,glazes and pastes

The first archaeological evidence reported for tile production in Portugal was discovered in Santo António da Charneca (SAC), late 15th or early 16th centuries' pottery kiln, south riverside of Tagus River. Samples from this kiln were studied with the use of non‐invasive spectroscopies, namely, μ‐Raman, ground‐state diffuse reflectance absorption, Fourier transform infrared and particle‐induced X‐ray or X‐ray fluorescence emission. These results were compared with the ones obtained for coeval tiles produced in Seville, Spain, originated from Portuguese archaeological sites, because it is well know that the Portuguese King Manuel the First imported in 1498 significant quantities of those tiles to decorate several palaces. The obtained results provided new spectroscopic insights, used to establish similarities but also clear differences regarding the SAC and the coeval Seville tiles found in Portugal. White glaze from both tiles gave evidence about the use of tin oxide as whitening agent and lead oxide as glassy agent. Cobalt oxides were also used as blue pigments in the two production centres. The brown and amber pigments in the samples from SAC derive from the manganese oxides dispersed in the lead–tin glaze, and kentrolite crystals were identified by μ‐Raman in these tiles. In the arista and cuerda‐seca tiles from Seville, diopside was detected. Divalent copper also exists in the green glaze matrix but in small amounts, which did not allow the Raman detection of the copper compound's microcrystals. However, diffuse reflectance measurements point to malachite green as responsible of green coloration. The Seville pastes contain calcium carbonate, although the SAC pastes do not evidence significant amounts of that compound in its composition. All the SAC pastes evidenced a high silica level, and quartz and anatase were clearly detected in the paste and possibly kaolinite. The Raman signals of orthoclase and calcium carbonate were detected in the Seville tiles. Copyright © 2014 John Wiley & Sons, Ltd.     

UV-spectral changes for some azo compounds in the presence of different solvents

The electronic absorption spectra of four azo dyes with different substituents (such as Cl, I, OH) are determined at room temperature in twenty-one solvents with different polarities. The electronic transitions of azo dyes are interpreted. Linear solvation energy relationships have been investigated for solvatochromic behaviors and solute-solvent interactions of azo dyes. Linear solvation energy relationships were performed by multiple linear regression analysis using dielectric function, refractive index function and Kamlet-Taft parameters. We have observed that the hydrogen bonding acceptor ability and the induction-dispersive forces of solvent molecules have caused the bathochromic shift in absorption maxima of azo dyes.     

Anomalous aggregation of squaraine dyes in confined solutions

Enhanced aggregation of squaraine (SQ) dyes in solution capillary layers in contrast to the monomer behavior of the bulk solutions has been observed through differences in electronic absorption spectra of the capillary and bulk SQ solutions of the same concentration. The spectra of the capillary solutions were also different from spectra of SQ condensed films. The spectral differences were dependent on both chemical structure of the dye used and the solvent. It was found that aggregation was stronger in dimethylformamide (DMFA) capillary solutions when compared to the chloroform capillary solutions where aggregation was negligible. It is proposed that the driven force of the observed phenomena is enhanced adsorption of SQ molecules and formation of a liquid crystalline state of the solution near the liquid/solid interface.     

A DFT/TD‐DFT study for the ground and excited states of peramine and some pyrrolopyrazinone compounds

Peramine, a heterocyclic natural molecule, reveals two main, different in nature, electronic absorption bands. Theoretical calculations at the TD‐B3LYP/6–311++G(d,p) level of theory show that the electronic excitations are connected predominantly with π → π^* and charge‐transfer (CT) transitions. Excitation of electrons from the pyrrolopyrazinone ring to the side chain plays a role in creating the CT transition. The character and energy of the first 30 singlet–singlet electronic transitions have also been investigated for the most stable conformation of peramine. Copyright © 2009 John Wiley & Sons, Ltd.     

Inner‐shell chemical shift of DNA/RNA bases and inheritance from their parent purine and pyrimidine

Inner‐shell electronic structures, properties and ionization spectra of DNA/RNA bases are studied with respect to their parent pyrimidine and purine species. Density functional theory B3LYP/aug‐cc‐pVTZ has been employed to produce the geometries of the bases, whereas LB94/et‐pVQZ//B3LYP/aug‐cc‐pVTZ is used to calculate site‐related Hirshfeld charges and core (vertical) ionization energies, as well as inner‐shell spectra of C1s, N1s and O1s for DNA/RNA bases and their parent pyrimidine and purine species. The site‐dependent variations of properties indicate the changes and inheritance of chemical environment when pyrimidine and purine become substituted. In general, although the changes are site‐dependent, they are also ring‐dependent. Pyrimidine bases change less significantly with respect to their parent pyrimidine than the purine bases with respect to their parent purine. Pyrimidine bases such as uracil, thymine and cytosine inherit certain properties from their parent pyrimidine, such as the Hirshfeld charge distributions and the order of core ionization energy level etc. No particular sites in the pyrimidine derivatives are engaged with a dramatic chemical shift nor with energy crossings to other sites. For the core shell spectra, the purine bases inherit very little from their parent purine, and guanine exhibits the least similarities to the parent among all the DNA/RNA bases.     

NLOphoric Red Emitting Bis Coumarins with O-BF<Subscript>2</Subscript>-O core - Synthesis,Photophysical Properties and DFT Studies

The red emitting dyes were synthesized by employing coumarin core as a donor and boron-bonded coumarin as an acceptor. 7-(N,N-Diethylamino)-coumarin 3-aldehyde was reacted with 3-acetyl-4-hydroxy-coumarin, 7-(N,N-diethylamino)-3-acetyl-4-hydroxy-coumarin and 3-acetyl-4-hydroxy-1-methyl-quinolone to form the corresponding chalcones. The synthesized chalcones were though red shifted as compared to the parent coumarin, and were not emitting in red region. The BF₂-complexation was used as a tool to introduce a red shift in the molecules. The BF₂-complexes synthesized were found to be red emitting and show higher one photon absorption cross section. The solvatochromism shown by these dyes was studied in the light of solvent polarity parameters. DFT calculations were used to understand the photophysical properties of the synthesized dyes. NLO properties of the dyes were estimated by solvatochromic and computational methods. All the molecules synthesized were characterised with the HRMS and NMR spectral Analysis.     

Spectroscopic study of a representative polar cap of buckminsterfullerene: Cyclopentacorannulene

The spectroscopic properties of corannulene and cyclopentacorannulene are examined by use of absorption and steady-state fluorescence measurements. A red shift in the emission maxima of cyclopentacorannulene is noted with respect to the emission maxima in the corannulene spectrum. Similar differences in the absorption spectra of both molecules are also observed. Reasons for the dissimilarities in the absorption and emission spectra of these molecules are discussed. The fluorescence quantum yields and lifetimes of the molecules measured in organic solvents are reported. The fluorescence quantum yield and lifetime of cyclopentacorannulene are lower than those of corannulene. This difference is attributed to the highly strained and nonplanar structure of cyclopentacorannulene. The effectiveness of nitromethane as a quencher of corannulene and cyclopentacorannulene fluorescence is examined. In contrast to previously reported results, the fluorescence of these molecules is quenched by nitromethane. Fluorescence quenching of the molecules has been attributed to complex formation in the ground state, i.e., static quenching.     

YH,YD,YT分子基态的结构与势能函数

在Y的有效核势近似下, 对H分别选6-311++G(3df,2pd), AUG-cc-PVTZ, AUG-cc-PVQZ基组, 应用密度泛函理论的B3LYP方法, 优化计算了YH(D,T)分子基态的能量, 平衡结构, 和谐振频率.根据原子分子反应静力学原理, 导出了YH(D,T)分子基态的合理离解极限. 通过优化计算结果和已有的实验和理论数据对比, 得出LANL2TZ/AUG-cc-PVQZ混合基组为对体系进行计算的最优基组. 基于此, 在B3LYP/LANL2TZ/AUG-cc-PVQZ水平对YH(D,T)分子基态的势能面进行了单点能扫描. 并采用最小二乘法拟合得到了相应的Murrell-Sorbie势能函数. 计算出了这些分子的力常数(f₂, f₃, f₄)和光谱常数(B_e, α_e, ω_e, ω_eχ_e, D_e).结果与已有的实验数据符合得很好.     

Single‐cell resolution in high‐resolution synchrotron X‐ray CT imaging with gold nanoparticles

Gold nanoparticles are excellent intracellular markers in X‐ray imaging. Having shown previously the suitability of gold nanoparticles to detect small groups of cells with the synchrotron‐based computed tomography (CT) technique both ex vivo and in vivo, it is now demonstrated that even single‐cell resolution can be obtained in the brain at least ex vivo. Working in a small animal model of malignant brain tumour, the image quality obtained with different imaging modalities was compared. To generate the brain tumour, 1 × 10⁵ C6 glioma cells were loaded with gold nanoparticles and implanted in the right cerebral hemisphere of an adult rat. Raw data were acquired with absorption X‐ray CT followed by a local tomography technique based on synchrotron X‐ray absorption yielding single‐cell resolution. The reconstructed synchrotron X‐ray images were compared with images obtained by small animal magnetic resonance imaging. The presence of gold nanoparticles in the tumour tissue was verified in histological sections.     

Fluorescence Characteristics of Variously Charged Asymmetric Monomethine Cyanine Dyes in the Presence of Nucleic Acids

Three asymmetric monomethine cyanine dyes bearing one, two, and three positive charges have been synthesized, and their absorption and fluorescence characteristics in the presence of nucleic acids were studied. The maxima of their longest wavelength absorption band lie between 500 and 520 nm. The dyes do not show fluorescence of their own in TE buffer (pH = 7.5), but become strongly fluorescent (Q_F = 0.2–0.6) on binding to double-stranded DNA. The fluorescence maxima of the investigated dye-dsDNA complexes are in the region of 530–550 nm. The influence of the dye/DNA ratio on both the position and intensity of the fluorescence maxima of the complexes is investigated.     

Solvent Polarity and Excitation Wavelength Dependence of the Dual Fluorescence in N,N-Diethyl-4-Nitrosoaniline

Dual fluorescence in N,N-Diethyl-4-nitrosoaniline (DENA) has been studied employing absorption, excitation and emission spectroscopic techniques and computational methods. The absorption and fluorescence spectra of DENA were measured in solvents of various polarities at room temperature. The emission spectra of DENA were found to exhibit a single emission band in non polar solvent (cyclohexane) and in a highly polar solvent (acetonitrile). In the contrary, two emission bands were observed in medium polar solvents (tetrahydrofuran, 1,2-dichloroethane and dichloromethane) whereby the short (local excited; LE) and long (charge transfer; CT) emission maxima correspond to the emission maxima of the compound observed in cyclohexane and acetonitrile solutions, respectively. Moreover, the two emission bands have shown strong excitation wavelength dependence, and area normalization resulted in an iso-emissive point. The two emission maxima were in addition found to correspond to two excitation maxima in 3D fluorescence spectra. Further, two minima were obtained in potential energy surface calculation of DENA. From the experimental and computational results it was concluded that the dual fluorescence may be attributed to the presence of two different ground state structural conformers of DENA in equilibrium that are stabilized through solute-solvent interaction.