Dicyanopyrazine-linked porphyrin Langmuir–Blodgett films

We investigated the influence of arachidic acid/cadmium dication (AA/Cd2+) as a transfer promoter for the deposition of dicyanopyrazine-linked porphyrin (2-DCPP) Langmuir–Blodgett (LB) films on both hydrophobic and hydrophilic substrates. In the case of LB deposition on a hydrophilic substrate, the presence of AA/Cd2+ does not improve 2-DCPP LB deposition. The poor transfer in the case of the hydrophilic surface is believed to be due to 2-DCPP not wetting the surface during the down-stroke deposition, and this is not improved by the transfer agent. However, on a hydrophobic substrate, deposition of 2-DCPP is significantly improved by the presence of AA/Cd2+. Comparison of the UV–visible spectrum of a 2-DCPP LB film with that of 2-DCCP dissolved in chloroform reveals that the Soret and Q bands for the 2-DCPP LB film are broadened and red-shifted due to aggregation of porphyrin rings in the LB film. UV–visible spectral changes and ellipsometry as a function of the number of deposition layers suggest continuous transfer of 2-DCPP/AA onto the hydrophobic substrate and reproducibility in the deposition process. The Soret and Q bands of the 2-DCPP LB film upon acid vapor exposure have also been investigated, and these measurements may have chemical sensor applications.