Absorption spectral study of mixed chiral amino acid porphyrin Langmuir-Blodgett films

Absorption spectra were performed on Langmuir-Blodgett films of a new chira l amino acid porphyrin (Py) and its mixture with stearic acid (SA). Vertica l uniformity of the LB films has been demonstrated by the linear relationsh ip between the absorbance and the layer number of films. J-Aggregates were present when the film was transferred at various surface pressures and at d ifferent molar ratios of Py and SA. However, no aggregation was present for the molecules in the adjacent monolayers. The observed optical absorption spectra of mixed films were markedly dependent on the combination of Py. Wh en the molar ratio of Py was increased from 0.05 to 0.75, the absorption pe aks of Soret and Q bands bathochromically shifted ca. 5.5 and 2.2 nm. When the deposited pressure was increased from 5 to 35 mN/m, the absorption peak s of Soret and Q bands bathochromically shifted ca. 3.7, 3.2 nm and 3.5, 2. 2 nm for pure Py and 1:3 Py-SA mixed LB films, respectively. On a hydrophob ic substrate, the LB films showed a red shift of ca. 4.5 nm for Soret band compared with that on the hydrophilic substrate owing to their different en vironments.