Structure of Monolayers of Copper Tetra-(3-nitro-5-tert-butyl)-Phthalocyanine at the Air-water Interface.

The structure of floating layers of soluble copper tetra-(3-nitro-5-tert-butyl)-phthalocyanine (CuPc*) is studied through surface pressure-area (π-A) isotherms measured at various initial surface concentrations (N0) of CuPc*. In the gaseous layers, the CuPc* molecules are surrounded by a hydration sphere. Condensation of the layers under compression results in an increase in the tilt angle of the CuPc* molecules relative to the air-water interface. Though it is accompanied by a loss of weakly bound water, an inner part of the hydration sphere sustains compression and enters the condensed layers. Depending on the N0 and π values, the molecular tilt angle ranges from 30 to 90° indicating the phase states of the β-, α-, and x-types. The different nature of the bilayers formed through compression of the rare monolayers and through spreading of large amounts of CuPc* is stated.