The Phthalocyanine–Polystyrene Composite: Tuning the Optical Spectrum via Polymer-Triggered Phase Transformations of the Dye

This work reports on copper tetra(3-nitro-5-tert-butyl)phthalocyanine (CuPc*) exhibiting complex but well-controlled phase behavior. A key structural feature of this dye is the thermodynamically stable χ-type phase whose optical absorbance is red-shifted with respect to the CuPc* molecule. Small-angle X-ray scattering and optical spectroscopy have been used to watch the phase formation of CuPc* in the one-component system and binary composite with polystyrene (PS). The polymer exerts a powerful stabilizing effect on the lower phases of CuPc*, hence a manageable suite of the phase transformations β→α→χ is realized in the CuPc*–PS system. Regardless the phase type, the composite is highly transmissive in the blue-green region of the spectrum. Thus, it is applicable to reveal quantitative relationships between nonlinear optical properties and the supramolecular structure of phthalocyanines.