Phospholipids, labeled covalently by a fluorescent dye, are commonly applied in membrane biophysics. In this work, a molecular dynamics model of sulforhodamine attached covalently to a headgroup of 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine is developed. It is found that the incorporation of rhodamine-labeled phospholipids into a DPPC bilayer at the low concentration results in small perturbation of the bilayer. In the dye-labeled membrane, the sulforhodamine moiety binds favorably to a polar membrane interface, forming the tilt angle 44 degrees +/- 8 degrees to the bilayer normal. The deep location and binding of a bulk sulforhodamine fluorophore lead, therefore, to some 'softening' of the membrane structure. (C) 2009 Elsevier B. V. All rights reserved.