Tubular or Subsurface Morphology of Octabutoxyphthalocyanine upon Self‐Assembly in Polymer Matrices: Effect of the Casting Solvent

Abstract

Spontaneous phase-separated, controlled aggregate structures of photo- and electroactive molecules in polymer matrices are of interest for device fabrication. We show that the self-assembly of octabutoxyphthalocyanine (Pc) in polymer matrices leads to tubular morphology of Pc when the film is prepared with tetrachloroethane (TCE) and subsurface droplet morphology with chloroform. The same morphology is seen with both bisphenol A polycarbonate (BPAPC) and poly(methyl methacrylate) (PMMA) as the matrix. The subsurface morphology results from the rapid association of Pc in the polymer matrix, as the film forms. With the tubular morphology in the films prepared with TCE, percolation threshold is reached with a concentration of Pc as low as 3% (wt) in the polymer. Such phase-separated self-assembly occurs, without any annealing of the films. Even in the absence of the polymer, Pc crystallized from TCE also shows tubular morphology, whereas it exhibits a columnar morphology with chloroform. X-ray diffraction of Pc crystallized from either solvent shows the columnar stacking of the Pc molecules. However, the morphology is tubular when TCE is used. We attribute the difference in the morphology to the higher viscosity of TCE and the diffusion-limited growth, which causes the tubular morphology, whereas the instantaneous self-assembly in less-viscous chloroform leads to droplets. The solvent effect observed here could be used to tailor the morphology of such photoconductive molecules in polymer matrices.

Small molecule self‐assembly in polymer matrices

“…Films were cast from solutions of octabutoxy phthalocyanine (Pc) and polycarbonate (BPAPC) or poly (methyl methacrylate) (PMMA) in chloroform or 1,1,2,2‐tetrachloroethane (TCE). The SEM image (not shown here) of the films of Pc/BPAPC cast from chloroform consisted of a smooth surface, did not show any features and would tend to indicate that the small molecule was molecularly dispersed in the polymer matrix. However, the OM images shown in Figure indicate that self‐assembly had occurred and that the domains are sub‐surface.…”

“…The above studies with carbamates and biscarbmates used chloroform as the solvent to cast the films. Let us discuss a case where the self‐assembly is facilitated by π‐interaction, and two different solvents and polymers were used, with the structures shown in Figure .…”

A Molecular Chameleon: Reversible pH- and Cation-Induced Control of the Optical Properties of Phthalocyanine-Based Complexes in the Visible and Near-Infrared Spectral Ranges

“…For a long time, the origin of such behavior remained ambiguous. Initially, researchers tended to interpret the solvatochromic behavior of α-AlkO-substituted ZnPc complexes in terms of the formation of J-aggregates, via coordination of the α-O atom to the Zn ion of a neighboring molecule. − Indeed, the addition of pyridine to such aggregates could cause their dissociation with the formation of monomeric species. However, some research groups have proposed that this process occurs because of the protonation of molecules. − In particular, in chlorinated solvents, it can be caused by traces of HCl that inevitably form upon storage of CHCl 3 or C 2 H 2 Cl 4 , especially upon exposure to light.…”

α- and β-Substituted Metal-Free Phthalocyanines: Synthesis, Photophysical and Electrochemical Properties

“…A broad Q band was detected with higher intensity than that in DMF. However, they did not exhibit an additional absorption band beyond the Q band due to J-aggregation or protonation of meso-nitrogens [36][37][38][39]. UV-Vis spectra of the compounds 4 and 5 at different concentrations were recorded in DCM (a series of spectra can be seen in Figure 2 for compound 5).…”