Pressure-induced structure ordering of long-chain Fluorescein O322 molecules within the monolayer at the air/water interface was studied by rotating a sample trough using the second-harmonic generation technique. Azimuthal angle dependences of the polarized second-harmonic intensity (Ipp, Ips, Iss, and Isp) were measured for different degrees of monolayer compression. Ipp and Iss showed a 2-fold pattern, whereas Ips and Isp showed a 4-fold pattern. A set of theoretical equations was derived to interpret the observed pattern. The observed patterns agreed with the equations based on C2v symmetry, and the monolayer showed a definite crystalline structure in the 0.21 nm2/molecule region. These results showed that the transition of an initially disordered and heterogeneous dye monolayer into a fairly regular crystalline-like structure was characterized by continuous changes in the structure ordering of constituent molecules maintaining C2v symmetry.
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films
- Materials Chemistry