7, 8-Dimethyl-10-dodecyl isoalloxazine (DDI) is a derivative of "flavin", which is a good electron donor that is easily found in natural systems. DDI shows high electron transfer efficiency with electron acceptors in artificial electron transport systems made of Langmuir-Blodgett (LB) films. LB films exhibit a variety of morphologies according to the experimental conditions, and the electron transfer efficiency depends strongly on the morphology of the films. In previous studies, the morphology of LB films composed of DDI was not investigated sufficiently. The present study shows that rod-shaped domains are formed in LB films composed of DDI when the DDI monolayer is compressed beyond a specific limiting area. The formation mechanism for rod-shaped domains can be surmised from the surface pressure-mean molecular area isotherm curve and atomic force microscopy data. The fluorescence lifetimes of the rod-shaped domains or nondomains were measured. The data is discussed in terms of the suggested formation mechanism of rod-shaped domains. (C) 2013 Elsevier B.V. All rights reserved.