ABSTRACT
At present, it is generally recognized that a large number of near-UV or visible-light-absorbing dyes belongingtodi¨erentcategoriesoforganiccompoundsexhibitinterestingphotosensitizingproperties, whosecontrolcanleadtodi¨erenttypesofdamagingorbene©ciale¨ectsonbiologicalsystems,includinglivingorganisms[11].Aparticularlyprominentroleisplayedbyporphyrinsandtheirnaturalor syntheticallypreparedtetrapyrrolicanalogues,includingchlorophylls,porphycenes,purpurins,phthalocyanines,andnaphthalocyanines.Porphyrinsabsorbessentiallyallthewavelengthsincludedinthe sunemissionspectrum;hence,theyareespeciallyimportantforapplicationsinnaturalenvironments wherethesunrepresentsthesourceofthephotochemicallyusefullightwavelengths.Historically,the ©rstporphyrintobeisolatedwashematoporphyrin,whichwasextractedfromdriedbloodbytreatment withconcentratedsulfuricacidfollowedbysolubilizationwithethanol[12].§enamehematoporphyrinwasassignedbyHoppe-Seylerin1871[13],andthisporphyrinwas©rstusedasaphotosensitizer inhumansbyMeyer-Betzin1913[14],whoinjectedhimselfwithhematoporphyrinandsubsequently su¨eredaprolongedpainandswellinginlight-exposedskinareas.Aderivativeofhematoporphyrin, knownunderthecommercialnameofPhotofrin,wasinitiallyusedasaphotosensitizerforthePDTof tumors[7],whereashematoporphyrinitselfwasproposedasanenvironmentallyfriendlyphotoinsecticidalagent[15].Moreover,thetetrapyrroliccoreofporphyrinscanbechemicallymodi©edatdi¨erent levels,suchasthecoordinationofmetalionsatthecenterofthemacrocycleandaxialligandsinthe©«h and/orsixthcoordinationpositionsoftheion,aswellastheintroductionofsubstituentsintheperipheralpositionsofthepyrroleringsorthemesointer-ringcarbonatoms.Inthisway,thephysicaland chemicalpropertiesoftheporphyrinphotosensitizercanbetailoredtoorientatethemoleculetoward predetermined sites of a cell or tissue [16].
