Tailor made synthesis of the isomeric azoaromatics, HL1–HL4 [HL = (arylamino)phenylazopyridine] containing a single hydrophobic tail (Cn = C10 and C12) is described. The coordination induced C–N bond fusion synthetic protocol has been successfully used for the synthesis of the compounds, which are subsequently characterized using various spectroscopic techniques. The single crystal X-ray structure of compound HL4 has revealed that the hydrophobic chain in it orients itself with all-trans conformation of alkyl groups. Studies of their surface properties clearly demonstrate that these behave as surfactants. Amphiphilic properties of the compounds are followed by the studies of compression isotherms and their surface morphologies are studied with the use of high resolution field emission scanning electron microscopy (FE-SEM) as well as atomic force microscopy (AFM). Distinct differences in surface properties in the two HL isomers are observed and disposition of the hydrophobic tail with respect to the head group is shown to play a significant role in the organization process of the molecules at the air–water interface. Transferred monolayers of the above two isomeric compounds show agglomerated nano-domain structures. This phenomenon has been explained considering hydrophobic tail–tail repulsive interaction within the adjacent molecules. Surface properties of the double tail complex, [Co(L1)2]ClO4 (1) along with that of the single tail complex, [Co(L1)(L5)]ClO4 (3) are also reported. Amphiphilic behavior of the above azoaromatics are distinctly different than those in their metal free state. Notably, the double tail complex (1) favors bi-layer formation even at low surface pressure region (∼10 mN m−1). The single tail cobalt complex (3), on the other hand, forms a monolayer at high surface pressure region leading finally to the collapse at a very high pressure ∼60 mN m−1.
Abstract In 1,4 dibromonaphthalene (DBN) crystal, phosphorescence emission is observed in conformity with quasi‐one‐dimensional exciton motion. In pyrene doped DBN crystal, fairly intense delayed fluorescence (DF) and delayed excimer fluorescence (DEF) are observed on host singlet excitation though prompt excimer fluorescence (EF) is absent. EF emission, however, is observed on pyrene singlet excitation. These results suggest that host triplet excitons are trapped more efficiently at monomeric pyrene sites than at nascent excimeric pyrene sites. From temperature and guest concentration dependence studies of delayed emission intensities and lifetimes it is concluded that homofusion of an adventitious defect triplet and heterofusion of this defect with guest triplets produce DF and DEF at low temperature but at high temperature homofusion of guest triplets is the generative event of these delayed emissions.
Abstract Phosphorescence, fluorescence, delayed fluorescence, excimer fluorescence, and delayed excimer fluorescence of pyrene are studied in the host p‐terphenyl system. The delayed fluorescence and delayed excimer fluorescence are biexcitonic and exhibit a similar dependency of the emission intensity on temperature; they both originate in identical kinetic events. The excitation spectra for all the emissions are presented. The trapping of the host triplet excitons occurs more efficiently at monomer pyrene sites than at nascent excimeric pyrene sites. The conclusion is that the delayed excimer and delayed fluorescence are produced by the homofusion of defect triplets and the heterofusion of defect and guest triplets. The defect level situated below the host exciton band controls the thermal excitation processes and the luminescence characteristics by the thermal event \documentclass{article}\pagestyle{empty}\begin{document}$ T_{{\rm 1D}} \to T_{1{\rm D}}^* \to T_{1{\rm H}} |_{\to T_{{\rm 1G}}}^{\to T_{{\rm 1D}}}. $\end{document} .
Neutral tris-chelated chromium complex [Cr(L(a))(3)] (1a), and its surfactant derivatives [Cr(L(b))(3)] (1b), [Cr(L(c))(3)] (1c), and [Cr(L(d))(3)] (1d) (where L(a)=2-(4'-methoxyphenylazo)pyridine, L(b)=2-(4'-butyloxyphenylazo)pyridine, L(c =2-(4'-octyloxyphenylazo)pyridine, and L(d)=2-(4'-dodecyloxyphenylazo)pyridine) were synthesized. The molecular structure of compound 1a, determined by X-ray diffraction, showed that the local geometry around the metal center is a distorted octahedral with meridional coordination of the ligands. The structural parameters, spectroscopic data, and density functional theory (DFT) calculations on representative complex 1a suggest that ligand L(a) is predominantly an azo-anion-radical-type, and so the complex can be represented as [Cr(III)(L(a.-))(3)]. An assessment of their physicochemical and surface properties was performed with the aim of using these triple-tailed metallosurfactants as precursors for redox-responsive films. The surface-pressure-molecular-area isotherm measurement for compound 1d shows that the complex forms a stable Langmuir film at the air/water interface. The monolayer and multilayers were successfully transferred onto the quartz substrate and the platinum working electrode at a surface pressure of 10 mN m(-1) by the Langmuir-Schaefer (LS) technique. The LS films were studied by UV/Vis spectrometry, infrared spectroscopy, field-emission scanning electron microscopy, and atomic force microscopy. A good linear relationship between the absorbance at 370 nm and the thickness of the layers against the number of deposited layers indicated the uniformity and reproducibility of this transfer process. Voltammograms for platinum-surface-bound LS film of compound 1d showed that the redox response owing to the first oxidation is stable and reproducible after many cycles (>300 cycles). Spectroscopic studies and electrochemical measurements of compound 1d on the LS films revealed that these complexes are potential candidates for molecular devices.
We report here the effect of salt (KCl) on the interfacial surface activity of yeast alcohol dehydogenease (ADH) at air/water interface using the Langmuir−Blodgett technique. Effect of salt content in the water subphase on ADH structure has been studied. The change of area/molecule, compressibility, rigidity, and unfolding of ADH are insignificant up to 10 mM KCl concentration. The significant changes are observed above 0.1 M KCl concentrations. Observations are explained in the context of DLVO theory. FTIR study of amide band together with AFM imaging of ADH monolayer indicate that KCl perturbs the ADH monolayer by the increment of β-structure resulting into larger unfolding and intermolecular aggregates at high salt concentration.
Interaction of native ovalbumin (OVA) with 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) Langmuir-Blodgett monolayer has been studied at the air-water interface. A compressibility study shows the positive association with DPPC. Adsorption kinetics shows that the protein adsorption is a one-step process and the amount of protein adsorbed depends on the concentration of protein at the water subphase. Incorporation of protein into the DPPC layer is surface-pressure dependent. The compressibility study indicates that the DPPC-OVA interaction is hydrophobic in nature and structural reorganization is eminent to adjust the hydrophobic mismatch between DPPC acyl chains and OVA hydrophobic moieties. At higher pressure, OVA tends to squeeze out from the DPPC monolayer. A nanometer scale FE-SEM image confirms this observation. Globular aggregates of protein of dimension 60-80 nm were observed in DPPC-OVA supported film. Steady-state fluorescence spectroscopy suggests that the tryptophan residues of OVA are main emitting species. The blue shift of tryptophan fluorescence in supported film may be due to the tryptophan molecule of protein exposed to the hydrophobic air phase.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
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