Ivana Šloufová

Characterization and surface-enhanced Raman spectral probing of silver hydrosols prepared by two-wavelength laser ablation and fragmentation

A four step Ag foil laser ablation-Ag nanoparticle fragmentation procedure in ultrapure water was carried out both under argon and in air. Pulses of a high power Nd/YAG laser were used for laser ablation (1064 nm) and for the three step Ag hydrosol treatment in the absence of Ag foil in the sequence 1064-532-1064 nm. Transmission electron microscopy (TEM) and surface plasmon (SP) extinction spectra provide evidence of Ag nanoparticle fragmentation in the second and third step of the procedure carried out under argon. While polydispersity of Ag hydrosol increases in the second step, both the polydispersity and the mean size of the nanoparticles are reduced in the third step. Qualitative and quantitative surface-enhanced Raman scattering (SERS)/surface-enhanced resonance Raman scattering (SERRS) spectral probing of systems with Ag hydrosols and the selected adsorbates at 514.5 nm excitation shows that Ag hydrosols obtained in the second step of the preparation procedure carried out in air are the most suitable substrates for SERS/SERRS experiments performed at this excitation wavelength.

Synthesis and Photophysical Properties of New α,Ω-Bis(Tpy)Oligothiophenes and Their Metallo-Supramolecular Polymers With Zn2+ Ion Couplers

Five new α,ω-bis(tpy)bithiophenes and terthiophenes, each comprising two hexyl groups attached to oligothiophene block at different positions, were prepared using the Suzuki coupling strategy, characterized (NMR, IR, Raman, HRMS, UV/vis, fluorescence, cyclic voltammetry) and transformed to corresponding conjugated metallo-supramolecular polymers with Zn2+ ion-couplers. Reference oligomers with unsubstituted central blocks and their polymers are also reported. Photophysical properties of oligomers and polymers are described, analyzed with a help of DFT calculations, and correlated with the chemical constitution of oligomeric building blocks. Steric effects were shown to exceed the electronic effects of hexyl groups, and twisting the thiophene-thiophene bonds were shown to influence electronic spectra of oligomers and polymer more deeply than twisting the thiophene-tpy bonds. Outlying photoluminescence characteristics observed for some oligomers and polymers were shown to be consistent with the other data based on their analysis by the Stokes shift approach. Polymers prepared exhibited good constitutional dynamics in DMSO but only limited dynamics in THF solutions. IR and Raman spectra allowing identification of solid oligomers and polymers are also presented.

π-Conjugated Polyelectrolytes Derived from 2-Ethynylpyridine: The Effect of Quaternization Agent and Reaction Conditions on the Polymer Structure and SERS Characterization of Nanocomposites with Ag-Nanoparticles

The reaction of 2-ethynylpyridine (2EP) with stoichiometric equivalent of an alkyl halide RX (R is ethyl, nonyl, or hexadecyl and X is Br or I) gives a poly(N-alkyl-2-ethynylpyridinium halide) type ionic polymer that belongs to the family of π-conjugated polyelectrolytes (CPEs). Reaction conditions significantly influence configuration of the polymer main chains: polymerization in acetonitrile solution gives polymers with high content of cis units while bulk polymerization provides irregular cis/trans polymers. Increased regularity of the high-cis polymers is documented by the NMR and IR as well as SERS (surface enhanced Raman scattering) spectra measured on Ag-nanoparticles/CPE systems. Both polymerization processes give polymers in which 2EP monomeric units are ionized only from ca one half, which exhibit good stability in air and good solubility in polar solvents such as MeOH, DMF, and DMSO and those with N-ethylpyridinium groups even in water.

Bis­(acridine-N)(nitrato-O,O′)silver(I)

The title complex, [Ag(NO(3))(C(13)H(9)N)(2)], is the first complex of silver and acridine to be reported. The silver coordination is distorted trigonal. The N-Ag-N angle involving the N atoms of the acridine ligands is 145.84 (6) degrees. The nitrate ion coordinates to silver as an asymmetrically chelating bidentate ligand. The crystal structure consists of neutral complex molecules linked into chains by means of attractive pi-pi interactions among the parallel acridine ligands.

(Acridine-N)trichlorogold(III).

The title compound, [AuCl(3)(C(13)H(9)N)], is the first complex of gold and acridine to be reported. The coordination sphere of the Au atom is square planar. The crystal structure is built up of neutral complex molecules linked into chains by means of attractive pi--pi interactions between the parallel acridine ligands.

Effect of Ethanethiolate Spacer on Morphology and Optical Responses of Ag Nanoparticle Array–Single Layer Graphene Hybrid Systems

Single layer graphene (SLG) and two-dimensional (2-D) plasmonic Ag nanoparticle arrays assembled by chemisorption of ethanethiol (ET) molecules (AgNPs-ET) were employed as components of two types of hybrid systems designed for surface-enhanced Raman scattering (SERS) spectral probing of SLG localized in the vicinity of plasmonic NPs. Both hybrids were characterized by optical microscopy, transmission electron microscopy (TEM), surface plasmon extinction (SPE), and SERS microRaman spectral measurements at four excitation wavelengths spanning the 445-780 nm range. SERS spectral probing of the glass/SLG/AgNPs-ET hybrid prepared by overdeposition of SLG on glass by the array of ET-modified Ag NPs has shown that the chemisorbed ET acts as an efficient molecular spacer between SLG and Ag NPs surface which, in turn, enabled to obtain SERS spectra of SLG unperturbed by doping or strain. TEM imaging and SERS spectral probing of the second hybrid prepared by overdeposition of AgNPs-ET array on glass by SLG revealed removal of the adsorbed ET molecules and annealing of Ag NPs during the SLG deposition. The characteristics of the resulting glass/AgNPs/SLG hybrid system, namely (i) broad distribution of the annealed Ag NPs sizes and shapes, (ii) SPE curve covering the overall visible spectral region, (iii) absence of the ET spectral bands in SERS spectra, and (iv) fairly uniform SERS enhancement of the G and 2D mode of SLG in the 532-780 nm range in the straight sample geometry indicate that this hybrid can provide a suitable platform for investigation of the excitation wavelength dependence of combined SERS/GERS (graphene-enhanced Raman scattering) enhancement experienced by various molecular species brought into contact with SLG in this hybrid. Finally, weak optical effects attributed to increased reflectivity of SLG in the near field of Ag NPs arrays have been observed in the excitation wavelength dependence of the SERS spectra of both types of hybrid systems.