PREPARATION AND POLYMORPHISM OF THIN-FILMS OF UNSUBSTITUTED COBALT PHTHALOCYANINE

A new method for preparing thin films of unsubstituted cobalt phthaloc yanine (CoPc) is reported. CoPc was dissolved in mixed media consistin g of trifluoroacetic or trichloroacetic acid and trichloromethane and spread onto different aqueous subphases. In this way, thin solid films were formed on the surface that exhibit no surface pressure and break readily under mechanical stress. Films were transferred to hydrophobi c glass plates by using a horizontal lifting method. Changing the subp hase pH led to three different film phases (I-III) that were character ized essentially by electronic spectroscopy of monolayers transferred on solid substrates and Brewster angle microscopy of monolayers floati ng on the subphase as well. The narrow Q-band absorptions exhibited by phases II and III reveal increased ordering in the film structure. Th e strong red-shift in the Q-band for phase II reveals lateral stacking of the molecules, which would be expected for trivalent rather than f or divalent metallophthalocyanines. Polarized electronic absorption sp ectra recorded under oblique incidence were consistent with flat-lying molecules in all cases. Heating transferred films of phase II or III produced an additional film phase, IV, that shows marked in-plane anis otropy.