## 1 Introduction  
Optically active phthalocyanine (Pc) systems possess intense absorption bands and exhibit photoluminescence from the excited states. They are also very stable and resistant to chemical,thermal, or photochemical degradation. Moreover, it is particularly interesting that they act as effective photosensitizers. Following their irradiation, singlet oxygen is generated, which is used in photodynamic therapy (PDT) to kill selected cells [1; 2; 3]. This kind of activity can also be used against microbial cells. For example, [PERSON] et al. [4] reviewed antibacterial efficacy of phthalocyanines and noticed that Gram-positive bacteria are more sensitive to phthalocyanines than Gram-negative bacteria. This may be a result of differences in the cell structure. In general, the outer membrane present in Gram-negative species makes them more resistant. However, it is difficult to explain this phenomenon in detail without deeper understanding of the interactions, and it is impossible to generalize the antibacterial mechanism of the compounds. The interaction with bacterial cell and the cell's response strongly depends on the physicochemical properties of the materials (such as size, shape, structure, charge, etc.), as we have previously described [5]. One of the possible antibacterial mechanisms is interaction of the compounds with bacterial membrane [6], while the other is reactive oxygen species production [7]. In the case of phthalocyanines, [PERSON] et al. [6] underlined that cell binding is a key factor influencing their antibacterial activity. Thus, the susceptibility of bacteria depends on the kind of phthalocyanines. [PERSON] et al. [8] indicated that conjugation of phthalocyanines with antibiotics also enhances the antibacterial activity of phthalocyanine-sulfonamides conjugate against Gram-negative bacteria. In general, many articles about the antibacterial properties of Pcs as photosensizers have already been published. However, there is lack of reports on their activity against multi-drug-resistant microorganisms.  
Various carbon-based composites are fabricated to enhance the activity of materials, for example, in photocatalysis [9; 10]. Phthalocyanines have also been incorporated into graphene or other carbon structures for photocatalytic or optoelectronic applications [11; 12; 13]. On the other hand, specific graphene-based systems have been found to possess good antimicrobial properties [14; 15]. In our study, we wanted to combine antimicrobial effects caused by two different factors--graphite oxide flakes and phthalocyanines activated by light--and use them against bacteria causing infection of the root canals of teeth.  
The application of ZrPc/GO-based composite (ZrPc with lysine ligand, LYS; GO, graphite oxide) for antibacterial PDT has already been shown by us [16], where the action against _Staphylococcus aureus_ ATCC 6538, _Pseudomonas aeruginosa_ ATCC 27853, and _Escherichia coli_ (_E. coli_) ATCC 11229 was proven. In agreement with other studies, it was indicated that Gram-positive bacteria are more sensitive strains. However, the influence of irradiation on enhanced antimicrobial activity of bis(LYS)ZrPc/GO materials was observed, particularly in the case of _P. aeruginosa_ (a multidrug resistant pathogen), where minimal inhibitory concentration (MIC) was equal to 0.32 mg/mL in comparison to 40 mg/mL needed for the nonirradiated sample [16].  
The aim of this paper was to characterize two synthesized zirconium(IV) phthalocyanines, axially substituted with different ligands (hydrocarbon chains terminated with amino groups), which were used to obtain two hybrid materials with graphite oxide flakes. Optical properties of all systems were described, also showing singlet oxygen generation after red-near-infrared light exposition. The composite activities against two resistant _E. coli_ strains were tested.