Distribution of a water-soluble porphyrin in mixed monolayers evaluated by energy transfer

Mixed monolayers of a water-soluble tetra-anionic porphyrin (PO) with dioctadecyldimethylammonium bromide (DOMA) and methyl stearate (SME) have been formed by co-spreading, with the aim of achieving molecular recognition. The lateral distribution of PO in such monolayers has been investigated by Forster energy transfer from the amphiphilic oxacyanine dye S9 in a mixed monolayer of methyl arachidate (AME) and arachidic acid (AA). Mixed monolayers of PO:DOMA:SME, mixing ratios 1:4:X (X=32, 64, 160, 240, 320 and 480) were transferred to hydrophobic glass plates coated with S9:AME:AA=1:2:18 by vertical dipping. The system was excited with ultraviolet radiation (lambda=366 nm). The excitation energy of S9 is transferred to PO and the relative fluorescence intensity I-d/I-infinity (I-d in the presence and I-infinity in the absence of PO) of S9 at 420 nm was measured. The results indicate a homogeneous lateral distribution of PO, i.e. no cluster formation, for low densities of PO in mixed monolayers with DOMA and SME. (C) 1997 Elsevier Science Ltd. All rights reserved.