Surface organization and photochemistry of Langmuir-Blodgett (LB) monolayers of 10 mol-% 5,10,15,20-tetrakis( pentafluorophenyl) porphyrin (PFP) in an octadecylamine (ODA) matrix on. at quartz and tapered optical fiber surfaces are studied. Previous investigations of PFP films on. at surfaces had revealed that they exhibit a relatively long fluorescence lifetime (similar to 4 ns). In this Letter we show that the fluorescence lifetime of PFP films deposited on optical fiber-tapers with diameters between 10 and 20 mu m is ten times shorter than that measured for the. at surface, being about 0.3 ns. Besides, films on tapered fibers are found to aggregate into domains with typical sizes smaller than those on. at surfaces. (C) 2009 Elsevier B. V. All rights reserved.