D. Möbius

Monolayer assemblies with functional units of sensitizing and conducting molecular components: Photovoltage, dark conduction and photoconduction in systems with aluminium and barium electrodes

Abstract Vectorial charge separation was studied in assemblies in which a mixed monolayer of an indocarbocyanine dye with the chromophores in the layer plane, a chain-like π electron system oriented perpendicular to the layer plane, and a layer of acceptor molecules were sandwiched between metal electrodes. The cyanine dye was excited by light and the excited electron could move via the π electron system and the acceptor to the positively biased electrode. The logarithm of the photocurrent increases linearly with the bias voltage. If the conducting π electron system and the acceptor are absent, the photocurrent is about an order of magnitude smaller and its logarithm depends linearly on the square root of the bias voltage. In both cases the photocurrent is proportional to the light intensity and shows the same temperature dependence. The results are interpreted by assuming that the excited electron is transferred to some interlayer state by tunnelling (low temperature mode) or by thermal activation (high temperature mode). In the absence of the conducting element and the acceptor the electron moves to the positively biased electrode with a low probability. In their presence the electron is transferred to the interlayer states spaced one monolayer away from this electrode, and then tunnelling from there to the electrode is rate limiting. If these arrangements are sandwiched between metals of very different work functions (aluminium and barium) a photovoltage can be measured and is interpreted as being caused by a vectorial electron transfer through the molecular functional unit towards the metal with the smaller work function. The dark conductivity through fatty acid multilayers sandwiched between an aluminium and a barium electrode was measured and was interpreted. The hopping of electrons between interlayer states adjacent to the aluminium electrode is rate limiting.

Supramolecular assemblies of photochromic benzodithia-18-crown-6 ethers in crystals, solutions, and monolayersElectronic supplementary information (ESI) available: crystal data, data collection, and structure solution and refinement parameters. See http://www.rsc.org/suppdata/nj/b1/b110630a/

We studied the assembly of dithiacrown ether styryl dye (CSD) molecules in crystals, solutions, and films in the presence of metal cations. X-Ray diffraction data allowed us to conclude that the anion affects the supramolecular architecture of CSDs in the crystal, specifically, the type of stacking of the dye molecules. In solution, in the presence of Pb2+, CSD molecules with the betaine structure spontaneously form dimeric complexes consisting of two dye molecules and two metal cations, with a fixed mutual arrangement of the double bonds. The dimer complex is stable due to coordination between the anion substituent of one molecule and the metal cation located in the crown ether cavity of the other molecule. Irradiation of the dimer complexes leads to regio- and stereoselective [2 + 2]-cycloaddition, giving only one cyclobutane derivative of the eleven theoretically possible products. The other photoreaction studied for CSDs is reversible Z–E isomerization. Due to its specific structure, the betaine-type CSD is able to form the ‘anion-capped’ Z-isomer. Intramolecular coordination in the ‘anion-capped’ isomer enhances its stability and causes a sharp deceleration of its dark Z–E isomerization. The amphiphilic CSD forms relatively stable monolayers on distilled water and various aqueous salt subphases. The results obtained indicate that it is possible to distinguish between two types of the dye monolayer structures based on the presence of alkali or heavy metal cations in the aqueous subphase.

Complex methodological approach to the studies of natural microlayers at the air/water interface

The investigations of sea-surface microlayers are crucial for better understanding of the mechanisms and physico-chemical processes at natural phase boundaries which play an important role in the marine environmental protection and global climate change. Sea-surface microlayers were studied in an original sample without any pretreatment and as ex-situ reconstructed films after previous extraction of the sample by organic solvents of different polarity. For physico-chemical characterization of natural and ex-situ reconstructed sea-surface microlayer samples a complex methodological approach was applied. Monolayer techniques, Brewster angle microscopy, reflection spectroscopy and electrochemical methods were used. Samples were collected from a Middle Adriatic eutrophicated sea-lake. Results were compared and discussed with respect to previously reported results obtained by analysing the samples from the same area and from the Northern Adriatic.

Brickstone arrangement in J-aggregates on an amphiphilic merocyanine dye

Abstract J-aggregates formed in monolayers of an amphiphilic merocyanine dye were transferred onto solid supports and were investigated by scanning force microscopy (SFM). Islands of bulk phase deposited material were observed after the monofilm transfer onto mica. The islands are up to several μm 2 in area and several nm height. On these islands molecular resolution was achieved in the SFM. The dye molecules are arranged in a rectangular unit cell. The unit cell area was in agreement with data from surface pressure—area isotherms and with the dimensions of the dye molecule. Our SFM data were consistent with a brickstone arrangement of dye molecules in the J-aggregates.

Monolayers of the photosensitive benzodithia-15-crown-5 derivative.

Abstract The amphiphilic benzodithia-15-crown-5 styryl dye forms relatively stable insoluble monolayers on distilled water (collapse pressure is 34.5 mN m −1 ) and alkali metal cations (35.6–36.7 mN m −1 ) or heavy metal cations (24.2 mN m −1 for Ag + ) in the aqueous subphase. Three types of the dye monolayer structures depending on the subphase nature (water, alkali metal or heavy metal cations) have been distinguished from surface pressure-molecular area and surface potential-molecular area isotherms, as well as observed by Brewster angle microscopy (BAM). The ionoselective and photosensitive properties of the amphiphilic dye in monolayers have been studied in the presence of K + , Na + , Hg 2+ and Ag + cations in the aqueous subphases.

Studies of organic monolayers on thin silver films using the attenuated total reflection method

Abstract The attenuated total reflection method was used to study the influence of dye monolayers on surface plasmons.

Photosensitive and ionoselective properties of the amphipilic crown-ether dye in monolayers

Abstract Monolayers of the amphiphilic benzo-15-crown-5 styryl dye were prepared. Their ionoselective and photosensitive properties in the presence of K + or Na + cations in the aqueous subphases were investigated. The reversible changes of the reflection intensity (due to trans–cis–trans isomerization of the CC bound in dye molecule) can be observed only for complexes of the dye molecules in monolayers with cations from the aqueous subphase.

Monolayers of a novel ionoselective butadienyl dye

The novel amphiphilic benzodithia-18-crown-6 butadienyl dye (1) forms relatively stable insoluble monolayers on distilled water (collapse pressure of 41 mN/m) and on aqueous subphases containing alkali metal or heavy metal salts (collapse pressures in the range of 27-38 mN/m, respectively). The dye 1 monolayer organization depends on chromophore association and interactions (especially complex formation) with heavy and alkali metal ions as deduced from surface pressure-area and surface potential-area isotherms as well as reflection spectra and Brewster angle microscopy observations. Dye 1 undergoes specific interactions with Hg(2+) and Ag(+), respectively (formation of different complexes). Nonspecific interactions have been observed with other salts, such as KClO(4) or Pb(ClO(4))(2). Further, dye 1 monolayers on 1 mM Hg(ClO(4))(2) solution undergo reversible photoisomerization, in contrast to monolayers on water and other aqueous salt subphases.

Monolayers of an amphiphilic crown ether styryl dye.

Abstract The crown-ether styryl dye ( I ) was synthesized and its monolayers were prepared. The surface-active and optical properties of dye I were investigated. The surface pressure-molecular area and surface potential-molecular area isotherms for mixed monolayers of dye I and dipalmitoylphosphatidic acid at various aqueous salt subphases were measured.

Ionic selectivity of the surface-active derivatives of crown ethers in monolayers

Abstract The monolayer characteristics of the four surface-active derivatives of crown ethers (I–IV) with different ring size were studied under various conditions. The area per crown ether molecule in monolayers at the air-water interface increases with increasing size of the polyether ring, whereas the surface potentials remain almost the same. The areas per molecule are increasing significantly in the presence of various alkali metal cations in the aqueous subphase, especially in the case of K + . The highest absolute value was found for crown ether III with six oxygen atoms in the polyether ring. The surface potential values for all studied crown ethers decrease in the presence of the alkali metal cations. These effects can be explained as complex formation between crown ether in the monolayers and cations from the aqueous subphase. Using the recently developed Brewster angle microscopy, the differences of the monolayer morphology in the prescene and absence of the alkali metal cations in the aqueous subphase were monitored, providing additional evidence for complex formation.