A series of alkylnaphthalenes, namely 1,4-dimethylnaphthalene, 2,6-diethylnaphthalene, 2-ethylnaphthalene and pure naphthalene are not able to form Diels-Alder adducts with C60 fullerene but produce a series of 1:1 charge-transfer complexes (CTC) where the aromatic compounds act as donor and C60 as acceptor. The spectrophotometric analysis of these CTC has permitted to determine the equilibrium constants of the CTC formation at four different temperatures and the relative enthalpies and entropies of formation. The C60-alkylnaphthalenes and C60-naphthalene were identified as weakly bound CTC. Using the Mulliken theory of the CTC also the degree of charge transfer α was determined, confirming the results already suggested by the equilibrium constants, i.e., the weakly interaction between the donor and the acceptor considered.