Preferred PhTBP compounds include substituted or unsubstituted tetraphenyltetrabenzoporphyrin (hereinafter TPhTBP) compounds, including mesotetraphenyltetrabenzoporphyrin (hereinafter m-TPhTBP) compounds, which have the following formula: ##STR6## where R2, R3 and M are as defined above, R4 is a substituent group, and x is an integer from 0 to 3.