“…Though presenting high photodynamic killing activity toward many kinds of tumor cell lines [3,4], viruses [5][6][7][8], and bacteria [9], the clinical use of the natural hypocrellins is severely limited by their poor water solubility and low absorptivity in the phototherapeutic window (600-900 nm), which urged the evolvement of various hypocrellin derivatives, such as sulfonated HA [10], glycosylated HB [11], cyclodextrin-modified HB [12], quaternary ammonium group-substituted HB [13], and tyrosine-appended HB [14,15]. In this respect, the metal complexes of hypocrellins are very attractive because they can be prepared easily and the enhanced water solubility and improved absorptivity within the phototherapeutic window can be achieved simultaneously [16][17][18][19][20][21].…”