Application of back-scattering geometry in Raman spectroelectrochemistry of laser-absorbing polymer films on reflective metallic electrodes results in different degrees of doubling of excitation (by ...the incident and reflected beams) of the electrode/film/solution interfaces. Taking this into account, this method was first applied to study in situ galvanostatic polymerization of aniline on Pt-electrode in aqueous solutions of polymeric sulfonic acids distinguished by different rigidity of the main chain. Firstly, it was found that 532 nm laser radiation caused fluorescence in the solutions of phenyl-containing polyacids resulted in the Raman spectrometer overload. One can reduce fluorescence by increasing the incident angle of the laser beam on the electrode up to 20° (perpendicular direction is taken as 0°). Secondly, some of the polyacids were found to have intensive Raman bands in the range of characteristic Raman frequencies (1000–1800 cm−1) of polyaniline (PANI). In this case, subtraction of the solution background spectrum before starting the electropolymerization monitoring causes appearance of ever-growing negative Raman signals as the laser-absorbing PANI film grows on the reflective electrode. The above two issues are due to the double excitation of the thin solution layer before the electrode by the incident and reflected laser beams, the degree of this doubling decreasing as (1) the incident angle is increased and (2) the PANI film thickness grows. The distortive influence of the solution Raman spectrum on the real shape of PANI spectrum may be estimated and diminished by using the amplitude of ever-growing negative Raman signal in the area of water OH vibration (near 3440 cm−1) as a measure of the ever-decreasing reflectance of the working electrode. Using the developed approach, it was shown that evolutions of the relative portions of the imine nitrogen (near 1490 cm−1) and the radical-cation nitrogen (near 1340 cm−1) fragments in the Raman spectra of PANI recorded in the course of electropolymerization can be used as informative criteria for the explanation of the differences in the aniline polymerization rate in the presence of polyacids of different chemical structure.
Display omitted
•back-scattering Raman study on reflective electrode leads to double excitation of electrode/film/solution interfaces•excitation doubling depends on: laser incident angle; thickness of the laser-absorbing polymer film; its absorption spectrum•characteristic Raman bands (water 3440 cm−1) of solution before electrode can be used as a measure of its reflectance change.•this approach overcomes distortive influence of Raman-active species in solution on real shape of polymer film Raman spectra•in situ Raman study of PANI electrosynthesis in presence of polymeric acids with different chain rigidity was first performed
Stable nanosized germanium particles were synthesized in a liquid medium (acetone) by laser irradiation of single-crystal germanium plates under aerobic and anaerobic conditions at room temperature. ...Various experimental methods—optical spectrophotometry, atomic force microscopy, and dynamic light scattering—made it possible to detect stable nanosized Ge particles in acetone and record optical absorption and luminescence spectra depending on the time of laser irradiation in the presence and absence of oxygen. Particular attention is paid to the results of the effect of laser irradiation on the physicochemical properties of pure acetone.
The effect of addition of
J
-aggregates of polymethine dye into the hole-transport layer of an organic light-emitting diode (OLED) on its characteristics and operational stability was studied. ...Water-soluble PEDOT:PSS (poly(3,4-ethylenedioxythiophene)) and the interpolymer complex of polyaniline and poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAn-PAMPSA) were used as the matrices of polymer nanocomposites. The highest efficiency characteristics of the OLEDs with the considered structure were achieved using PAn-PAMPSA at a particular component ratio in the interpolymer complex. Additives of
J
‑aggregates did not significantly affect the efficiency characteristics of the OLEDs; however, an increase in the operational stability of devices was recorded.
The article represents a translated, revised, and updated excerpt from the book
Electroluminescent Organic Light-Emitting Diodes Based on Metal Coordination Compounds
, Rostov-on-Don: Yuzhn. Fed. ...Univ., 2015; ISBN 978-5-9275-1469-4 (see Additional Information). The measurement of performance characteristics of organic light-emitting diodes (OLEDs), including current–voltage, luminance–voltage, and spectral characteristics is described in detail in relaton to the laboratory measuring facility existing at the Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences. A detailed description of this setup, including the essential minimum set of instruments required for characterizing OLEDs, can serve as a guide for researchers embarking on experiments in the field of electroluminescence. The second part of the article describes the principal limiting factors for OLED efficiency.
The article represents a translated, revised, and updated excerpt from the book
Electroluminescent Organic Light-Emitting Diodes Based on Metal Coordination Compounds
, Rostov-on-Don: Yuzhn. Fed. ...Univ., 2015; ISBN 978-5-9275-1469-4 (see Additional Information). The main technological stages for manufacturing of laboratory samples for electroluminescence are described in general terms. The most popular laboratory techniques for the formation of thin semiconducting organic films, such as solution spin coating and vacuum thermal deposition, are considered in more detail. Some methodological approaches used in our laboratory are outlined. Measurements of the polymer layer thickness by the interference method and by atomic force microscopy are considered in detail. For the interference method, the principal sources of systematic errors are examined. Concerning atomic force microscopy (AFM), two techniques for measuring thickness are considered: the express technique (macro-needle scratching) and scratching with an AFM probe in contact mode. Systematic errors associated with the first technique are determined, followed by recommendations regarding its potential application. The last section highlights the necessary adjustment for calibrating thickness sensors during film deposition if the calibration is conducted based on macro-needle scratching results.
—J-aggregates of a carbocyanine dye (pyridinium salt of 3,3'-di-(γ-sulfopropyl)-4,5,4',5'-di(tieno-3'',2'')-9‑ethyl-tiatrimethine cyanine betaine) (CC) were studied via the high-resolution AFM method ...at the mesoscale and nanoscale. They were found to exist in two structurally different polymorphic forms of single layers and fibrils. The class of single-layer J-aggregates consists of irregular micron sheets and giant submicron tubes, whose structure is identical to tubular J-aggregates of other cyanine dyes. The fibrillar J-aggregates are composed of 3-nm-high fibrils forming the networks owing to merging and branching, as well as of “elementary” fibrils with a height close to the molecular sizes of dye. Structural models of elementary fibril with molecular “staircase” and “ladder” stacking types were proposed as well.
A crystallographic analysis of the images of destruction fragments of tubular monomethine dye
J
-aggregates has been performed for the first time. It is shown that the formation of characteristic ...zigzag fragments is caused by the unwrapping of cylindrical surface on plane. Possible cleavage directions for the monolayer forming the tube walls are considered and an interrelation between the destruction products and molecular packing of this monolayer is established.
Meso- and nanoscale structural polymorphism of monolayer
J
-aggregates of four cyanine dyes are investigated. Three mesoscale morphological types are observed: ribbons, rhombic leaves, and tubes. ...Tubes are formed during cylindrical spinning of ribbons. Lined substructure characterized by the line width of about 7 nm is found in the case of monolayers of monomethine cyanine dyes at the nanoscale.
Atomic force microscopy (AFM) and scanning near-field optical microscopy (SNOM) imaging of fibrillar J-aggregates of carbocyanine dye ...3,3′-bis(γ-sulfopropyl)-5,5′,6,6′-tetrachloro-1,1′-dioctylbenzimidacarbocyanine (C8S3) is performed on mica and glass substrates at room temperature. High resolution AFM imaging reveal that thick fibrils consist of narrow sub-fibrils. A model of an elementary fibril with a cross section 3 × 4 nm
2
in size is proposed. The SNOM measurements made in the contact mode indicate the high mechanical strength of the fibrillar J-aggregates.
PDF
