Antimicrobial Photodynamic Polymeric Films Bearing Biscarbazol Triphenylamine End-Capped Dendrimeric Zn(II) Porphyrin

Abstract

A novel biscarbazol triphenylamine end-capped dendrimeric zinc(II) porphyrin (<b>DP 5</b>) was synthesized by click chemistry. This compound is a cruciform dendrimer that bears a nucleus of zinc(II) tetrapyrrolic macrocycle substituted at the <i>meso</i> positions by four identical substituents. These are formed by a tetrafluorophenyl group that possesses a triazole unit in the <i>para</i> position. This nitrogenous heterocyclic is connected to a 4,4'-di(<i>N</i>-carbazolyl)triphenylamine group by means of a phenylenevinylene bridge, which allows the conjugation between the nucleus and this external electropolymerizable carbazoyl group. In this structure, dendrimeric arms act as light-harvesting antennas, increasing the absorption of blue light, and as electroactive moieties. The electrochemical oxidation of the carbazole groups contained in the terminal arms of the <b>DP 5</b> was used to obtain novel, stable, and reproducible fully π-conjugated photoactive polymeric films (<b>FDP 5</b>). First, the spectroscopic characteristics and photodynamic properties of <b>DP 5</b> were compared with its constitutional components derived of porphyrin <b>P 6</b> and carbazole <b>D 7</b> moieties in solution. The fluorescence emissions of the dendrimeric units in <b>DP 5</b> were more strongly quenched by the tetrapyrrolic macrocycle, indicating photoinduced energy transfer. In addition, <b>FDP 5</b> film showed the Soret and Q absorption bands and red fluorescence emission of the corresponding zinc(II) porphyrin. Also, <b>FDP 5</b> film was highly stable to photobleaching, and it was able to produce singlet molecular oxygen in both <i>N</i>,<i>N</i>-dimethylformamide (DMF) and water. Therefore, the porphyrin units embedded in the polymeric matrix of <b>FDP 5</b> film mainly retain the photochemical properties. Photodynamic inactivation mediated by <b>FDP 5</b> film was investigated in <i>Staphylococcus aureus</i> and <i>Escherichia coli</i>. When a cell suspension was deposited on the surface, complete eradication of <i>S. aureus</i> and a 99% reduction in <i>E. coli</i> survival were found after 15 and 30 min of irradiation, respectively. Also, <b>FDP 5</b> film was highly effective to eliminate individual bacteria attached to the surface. In addition, photodynamic inactivation (PDI) sensitized by <b>FDP 5</b> film produced >99.99% bacterial killing in biofilms formed on the surface after 60 min irradiation. The results indicate that <b>FDP 5</b> film represents an interesting and versatile photodynamic active material to eradicate bacteria as planktonic cells, individual attached microbes, or biofilms.