Chemosensitive chlorophyll derivatives: optical detection of various amines by synthetic 3-trifluoroacetyl-131-deoxo-pyropheophorbides in solution

Methyl 3-trifluoroacetyl-131-deoxo-pyropheophorbide-a (1) and its derivatives were prepared by modifying naturally occurring chlorophyll-a. The 3-trifluoroacetyl group of the synthetic pigments was reacted with amines in dichloromethane to give the hemiaminal-type adducts bearing blue-shifted absorption bands. The hemiaminal of metal-free chlorin 1 with butylamine was formed more preferably than were those of its metal complexes as well as its C17double bond; length as m-dashC18 (porphyrin) and C7–C8 analogs (bacteriochlorin). An increase of the steric hindrance around the nitrogen atom of amines reduced the production of hemiaminals and primary amines possessing a primary alkyl group were selectively detected by absorption spectral change in 1. Polyamines bearing a (2-aminoethyl)amino group were readily added to the trifluoroacetyl group of 1 to afford the hemiaminals stabilized by intramolecular hydrogen bonding of the resulting hydroxy group with the nitrogen atom of the 2-aminoethyl group. Therefore, ethylenediamine was quantitatively analyzed by fluorescence emission spectroscopy and could be quickly detected even at 1 nmol (=0.1 equiv) using 10−5 M solution (1 mL) of 1 in aerated dichloromethane.