Photo-activated thin films of porphyrins for reactive oxygen species generation

The use of a single component porphyrin thin-film for photodynamic antimicrobial chemotherapy is unexplored. Herein, a porphyrin with good film formation properties is used to make thin layers, by physical vapor phase deposition, that are stable in aqueous media and can generate singlet oxygen upon 650 nm excitation. The synthesis and photophysical studies, in solution and as thin film, of free base 5,10,15,20-tetra-(4-hexyloxyphenyl)porphyrin are described. The porphyrin was synthesized via modified Adler-Longo conditions. Thin films of this porphyrin were made on quartz glass via spin coating and via vapour-phase deposition. The porphyrin was studied, in solution and as thin film (without a polymer component or matrix), with UV-Vis spectroscopy and with steady-state and time-resolved photoluminescence spectroscopy. The spin coated films display sharp J-band emission at 741 nm, indicating J-aggregate formation, but are not stable in aqueous media. The thin films obtained via vapour-phase deposition do not show the J-band emission, but are stable. The detection of singlet oxygen generated by the porphyrin thin film using a chemiluminescent water-soluble singlet oxygen probe is reported.