Factors Affecting the Structural Organization of Hemicyanine Chromoionophores in Langmuir Monolayers

Rational Design of Hemicyanine Langmuir Monolayers by Cation-Induced Preorganization of Their Structure for Sensory Response Enhancement

“…However, we call Ba 2+ ions inert for HCS due to the fact that such Ba−HCS interaction does not lead to changes in positions of any absorbance bands in its monolayer spectra (Figures 4b and 5, curves 1 and 2), signifying that complex formation does not take place. This fact can be understood in the comparison with an earlier established 26,29 behavior of HCO Langmuir monolayers, the simultaneous presence of metal cations in water subphase and chloroform at the interface leads to the formation of unstable complexes with "sandwich" structures in head-to-head orientation. Decomplexation takes place after chloroform evaporation, whereas the sandwich structure is stabilized by π−π interactions that only strengthen upon monolayer compression.…”

“…Such behavior is in agreement with the key role of the presence of organic solvent at the interface at the initial stage of monolayer formation in the preorganization of such monolayers on subphases containing inert cations discovered earlier for HCO. 29 In the case of the monolayer formed on barium perchloratecontaining subphase, the behavior of the system differs drastically. Introduction of the same amount of mercury perchlorate into the system leads to significant changes of both UV−vis reflection−absorption spectra (Figure 5a, curves 2 → 5) and X-ray reflectivity pattern (Figure 5b, curves 2 → 5).…”

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.…”

“…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).…”

“…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.…”