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Lawsone isomers, lawsone ether and bilawsone for dye-sensitized solar cells applications: DFT and UV–Vis studies
摘要： Structural and optoelectronic properties of lawsone (L), lawsone ether (LE) and bilawsone (BL) were studied theoretically using the DFT and time-dependent DFT methods with hybrid functional B3LYP5 and 6-311G (2d,p) basis set. For the monomer lawsone molecule, isomerization reaction between two rotational isomers was analyzed based on a thermodynamic approach. The electronic spectra of the dyes molecules in a vacuum and solvents (DMSO and CH2Cl2) were computed. The maximum wavelengths were found at 355e408 nm for the LE and 350e448 nm for BL that indicated bands shift to visible range compared to L (340 nm). The UVeVis spectra of the L and BL were measured experimentally in DMSO solution. For the BL, a broad and intensive band was observed in a visible region at 452 nm that apparently would favour sensitizing ability of the dye. The optoelectronic properties of the LE and BL showed them as more promising candidates for DSSCs applications compared to the individual lawsone dye.
关键词： Lawsone ether,Dye-sensitized solar cells,Lawsone isomers,DFT/TD-DFT,Bilawsone,UVeVis/vibrational spectra
更新于2025-09-19 17:13:59
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The Structure Optimization of Phenanthroimidazole Based Isomers with External Quantum Efficiency Approaching 7% in non-doped Blue OLEDs
摘要： In this work, four phenantroimidazole (PI) based isomers TPA-PPI-PBI, TPA-PPI-NPBI, PBI-PPI-TPA and NPBI-PPI-TPA for high-efficiency deep-blue organic light-emitting diodes (OLEDs) have been designed and synthesized. The structure-property relationship is systematically studied. Devices based on TPA-PPI-PBI, TPA-PPI-NPBI, PBI-PPI-TPA and NPBI-PPI-TPA achieved deep-blue emissions with the Commission Internationale de L'Eclairage (CIE) coordinates of (0.15, 0.07), (0.15, 0.07), (0.15, 0.09) and (0.15, 0.05) and high external quantum efficiencies (EQEmax) of 4.12%, 4.66%, 6.88% and 5.59%, respectively. Especially the PBI-PPI-TPA based device exhibited negligible efficiency roll-off with EQE 6.48% at practical 1000 cd m-2. Moreover, the EQE is still above 5% even at a high brightness of 10,000 cd m-2. Comparing the four isomers, we found that substituent at the C2 position of PI core has a significant influence on the emission wavelength and CIE coordinates. This work provides a rational design strategy that modifying electron acceptor (A) at the C2 position and electron donor (D) at the N1 position of PI core will be an effective way to fabricate high-performance PI-based bipolar emitters.
关键词： deep-blue,isomers,phenanthroimidazole,external quantum efficiency,OLEDs
更新于2025-09-19 17:13:59
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Laser detection of nuclear spin isomers of ethylene molecules
摘要： We report the making of a double-beam laser spectrometer to measure absorption spectra in the n5 + n9 combination vibrational band of ethylene in the region of l = 1.6 mm. The spectrometer is used to find a portion of the spectrum that has well-resolved absorption lines of all four nuclear spin isomers of ethylene molecules. The rotational quantum numbers of these absorption lines and the nuclear spin isomers of ethylene molecules responsible for them are identified.
关键词： spectroscopy of ethylene molecules,nuclear spin isomers of molecules,laser spectroscopy
更新于2025-09-16 10:30:52
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Electronic properties of oxidized cyclometalated diiridium complexes: Spin delocalization controlled by the mutual position of the iridium centres
摘要： Four cyclometalated diiridium complexes, with IrCp*Cl (Cp* = η5-C5Me5?) termini bridged by 1,4- and 1,3-bis(p-tolylimino-ethyl)benzene (1, 2), or 1,4- and 1,3-bis(2-pyridyl)benzene (3, 4), were prepared and characterized by nuclear magnetic resonance (NMR) spectroscopy and single-crystal X-ray diffraction (complexes 1, 2 and 4). The two iridium centres in complexes 1 and 3 are thus bound at the central benzene ring in the para-position (trans-Ir2), while those in complexes 2 and 4 in the meta-position (cis-Ir2). Cyclic voltammograms of all four complexes show two consecutive one-electron oxidations. The potential difference between the two anodic steps in 1 and 3 is distinctly larger compared to 2 and 4. The visible - near-infrared (NIR) - short-wave infrared (SWIR) absorption spectra of trans-Ir2 monocations 1+ and 3+ are markedly different from those of cis-Ir2 monocations 2+ and 4+. Notably, strong near-infrared electronic absorption appears only in the spectra of 1+ and 3+ while 2+ and 4+ absorb only weakly in the NIR-SWIR region. Combined DFT and TD-DFT calculations have revealed that (a) 1+ and 3+ (the diiridium-benzene trans-isomers) display HOSO and LUSO evenly delocalized over both molecule halves, and (b) their electronic absorptions in the NIR-SWIR region are attributed to mixed metal-to-ligand and ligand-to-ligand charge transfers (MLCT and LLCT). In contrast, cis-isomers 2+ and 4+ do not feature this stabilizing π-delocalization but a localized mixed-valence state showing a weak IVCT absorption in the SWIR region.
关键词： Mixed-valence State,Cyclometalated Isomers,Cyclic Voltammetry,Diiridium Complex,Spectroelectrochemistry
更新于2025-09-12 10:27:22
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Isomerization and Properties of Isomers of Carbocyanine Dyes
摘要： One of the important features of polymethine (cyanine) dyes is isomerization around one of C–C bonds of the polymethine chain. In this review, spectral properties of the isomers, photoisomerization and thermal back isomerization of carbocyanine dyes, mostly meso-substituted carbocyanine dyes, are considered. meso-Alkyl-substituted thiacarbocyanine dyes are present in polar solvents mainly as cis isomers and, hence, exhibit no photoisomerization, whereas in nonpolar solvents, in which the dyes are in the trans form, photoisomerization takes place. In contrast, 3,3′-diethyl-9-(2-hydroxy-4-methoxyphenyl)thiacarbocyanine occur as trans isomers and exhibit photoisomerization in both polar and nonpolar solvents. The behavior of these dyes may be explained by the fact that the phenyl ring of the substituent in their molecules can be twisted at some angle, removing the substituent from the plane of the molecule and reducing its steric effect on the conformation of the trans isomer. In some cases, photoisomerization of cis isomers of meso-substituted carbocyanine dyes is also observed (for some meso-alkyl-substituted dyes complexed with DNA and chondroitin-4-sulfate; for 3,3′-diethyl-9-methoxythiacarbocyanine in moderate polarity solvents). The cycle photoisomerization–thermal back isomerization of cyanine dyes can be used in various systems of information storage and deserves further investigation using modern research methods.
关键词： isomerization,meso-substituted cyanines,trans and cis isomers,carbocyanine dyes
更新于2025-09-09 09:28:46
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Analyzing the Influence of Substituents on Proton Tautomerization - a Comparison of tetra- <i>tert</i> -Butyl Phthalocyanine Isomers
摘要： We present a comparative study of tetra-tert-butyl phthalocyanine (ttbPc) isomers on a Ag(111) surface by means of low temperature scanning tunneling microscopy to analyze the influence of substituents on the tautomerization, a proton transfer reaction, in single molecules. By comparing ttbPc with the well studied phthalocyanine (H2Pc) molecule, we demonstrate a decoupling from the surface by the tert-butyl substituents. A comparison between the four ttbPc isomers, which naturally exist due to different bonding positions of the tert-butyl groups on the macrocycle, reveals a significant influence of the structural differences on their tautomerization behavior, as evidenced by a switching rate which varies by up to a factor of four between ttbPc isomers. These findings can be understood by an energetic landscape of the proton switch which links the binding distance of tert-butyl groups with the height of potential barriers. This model is supported by the analysis of two types of deprotonated ttbPc molecules with the molecular nanoprobe (MONA) technique.
关键词： tetra-tert-butyl phthalocyanine,proton transfer,scanning tunneling microscopy,tautomerization,isomers
更新于2025-09-09 09:28:46
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[ACS Symposium Series] Raman Spectroscopy in the Undergraduate Curriculum Volume 1305 || Quantitative Analysis of Xylene Mixtures Using a Handheld Raman Spectrometer
摘要： Xylene isomers (meta-xylene, ortho-xylene, and para-xylene) have been extensively analyzed by different instrumental methods. In this chapter, xylene isomers and their mixtures were analyzed qualitatively and quantitatively by Raman spectroscopy. First, we identified peaks that discriminated each isomer along with peaks that remain unchanged regardless of isomeric form. We used theoretical calculations to aid in the peak assignments. Then, we tested the efficacy of the technique in qualitatively and quantitatively apportioning isomeric mixtures of xylenes.
关键词： Xylene isomers,DFT calculations,Raman spectroscopy,quantitative analysis,handheld Raman spectrometer
更新于2025-09-04 15:30:14