A series of Sn(IV) porphyrins with 4-methoxy-(1-SnPor), 3-methoxy-(2-SnPor), 4-hydroxy-(3-SnPor) and 3-methoxy-4-hydroxyphenyl (4-SnPor) meso-Aryl rings have been synthesized and characterized. 1-4-SnPor have relatively high singlet oxygen quantum yields in the 0.65-0.68 range in DMSO due to the heavy atom effect of the Sn(IV) ion. The lowest energy Q bands of the complexes lie at 612, 602, 615 and 620 nm, respectively. In the context of 4-SnPor, this represents an 18 nm red shift relative to the spectra of Sn(IV) tetraphenylporphyrin and 2-SnPor, which has methoxy groups at a meta-position. The in vitro photodynamic therapy (PDT) activities of 1-4-SnPor were determined against MCF-7 breast cancer cells through illumination for 20 min with a Thorlabs M625L3 (240 mW.cm-2) light emitting diode (LED) that has an output maximum at 625 nm and a Modulight illumination kit providing a dose of 1.7 J.cm-2 at the well-plate. The IC50 value of 7.1 μM for 4-SnPor is significantly lower than the values of 14.7, 16.5 and 11.2 μM for 1-3-SnPor, respectively, due to the significant red shift of its Q00 band that results in a better match with the output maximum of the LED. 1-4-SnPor were found to have relatively high photodynamic antimicrobial activity against planktonic Gram-(+) Staphylococcus aureus (S. aureus) and exhibited moderate activity against Gram-(-) Escherichia coli (E. coli) bacteria upon illumination with the Thorlabs M625L3 LED for 75 min providing a dose of 6.5 J.cm-2 at the well-plate. Log10 reduction values of 7.62 and > 2.40-2.94 were obtained with 1 and 5 μM solutions in 1% DMSO/PBS, respectively. The photodynamic antimicrobial activities were also investigated against S. aureus and E. coli biofilms.