Artificial Iono‐ and Photosensitive Membranes Based on an Amphiphilic Aza‐Crown‐Substituted Hemicyanine

Abstract

Artificial iono- and photosensitive membranes based on an amphiphilic aza-crown-substituted hemicyanine are assembled on liquid and solid supports and their aggregation behaviour, which is influenced by the binding of metal cations and surface density, is studied. The photoinduced charge-transfer properties of an analogous non-amphiphilic hemicyanine in solution are also demonstrated. An asymmetric sandwich dimer model is proposed and existence of such dimers in solution is evidenced by transient absorption and fluorescence anisotropy experiments. Changes in absorption and emission spectra, as well as compression isotherms of the amphiphile observed in the presence of cations, are discussed in terms of 2D molecular reorganisation. Surface-pressure-controlled reversible excimer formation at the air-water interphase and excimer-type emission of Langmuir-Blodgett films in the presence of cations are demonstrated and are discussed on the basis of fibre-optic fluorimetry and fluorescence microscopy results.

The Effect of Alkyl Substituent Length on Receptor Properties of Dithiaaza-Сrown-Hemicyanine MonolayersThe Effect of Alkyl Substituent Length on Receptor Properties of Dithiaaza-crown - Hemicyanine Monolayers

“…[7,20,33,42] In this case, recorded monolayer compression isotherms (Figure 4) are significantly different to the ones obtained on pure water subphase in overall form and the position of the bend. In addition, more importantly, the value of mean molecular area, at which surface pressure begins to increase, is shifted towards higher values for all three studied compounds.…”

“…[20] Since chromophoric part of the molecules studied in the present work is completely identical and crown ether moiety differs only by two sulfur atoms, it would be natural to suppose that such aggregation happens in our case as well. Such aggregation inhibits efficient analyte binding due to blocking of the crown-ether moiety by the neighbouring molecule in the aggregate (Scheme 3,a).…”

“…Moreover, the difference between these mean molecular area values for all three molecules on barium-containing subphase is much smaller (around 20 Å 2 ) than in case of pure water subphase (60 Å 2 between ChIP12 and ChIP16, and around 40 Å 2 between ChIP16 and ChIP21). Most probably, barium cations preorganize monolayer via weak interaction with dithiaaza-crown ether moiety of the studied molecules in the same way as it was for analogous azacrown substituted hemicyanine dye [7,20,33,42] and the resulting repulsion between the likely charged chromoionophoric groups provides the main contribution to the monolayer structure, while the length of alkyl chains are not as important (Scheme 3,b).…”

“…[12][13][14][15][16][17][18] Moreover, simultaneous inclusion of nitrogen atom into the crown-substituent of a coloured molecule as a part of both ionophoric and chromophoric moieties is an easy way to impart the chromoionophoric power to the dye molecule and obtain a spectral response to metal cation binding since their interaction with the nitrogen atom will reduce the overall chromophore conjugation and thus change the photophysical properties of the system. [5][6][7][8][9][10][11][19][20][21][22][23] In this regard, aza-crown substituted hemicyanines represent one of the most promising compounds for sensory applications due to the combination of hemicyanine spectral properties (absorbance and fluorescence in visible range), crown ether receptor ability and ease of chemical modification. [5,12,17,[24][25][26][27][28][29][30][31][32] However, most studies concerning the sensory properties of such crown-substituted hemicyanines were done in solution.…”

“…One of the most efficient methods to achieve this is LangmuirBlodgett technique, which allows formation of ultrathin organized films on almost any type of substrates. [7,20,[33][34][35][36][37][38][39] One of the principal chemical modifications of the hydrophilic hemicyanine molecules needed to use this technique is addition of hydrophobic alkyl chains to attain amphiphility in order to make the molecule surface active. However, the effect of the length of such substituent on the sensory properties of different compounds remains absolutely unstudied.…”