A series of novel substituted fulleropyrrolidines have been synthesized and characterized. A correlation between the substituent structure and the spreading behavior at the air-water interface has been proposed through the systematic study of their Langmuir films. This evidences that only some derivatives are suitable to from true monolayers at the air-water interface, because of the strong pi-pi intermolecular attractive forces among C-60 spheres. The factors that influence the nature of the floating layers on the water subphase have been identified. At last, tuneable parameters for the preparation of real and stable monolayers of fullerene derivatives have been proposed.