The photophysical properties of two N,N'-bis-alkyl-1,4,6,8-naphthalenediimide (DCN1 and DCN2) have been studied in chloroform and N,N-dimethylformamide solvents. The ability of DCN2 in N,N-dimethylformamide to detect metal cations have been monitored by the fluorescence emission spectroscopy. It has been shown that the fluorescent intensity is very sensitive to the concentration of Fe3+ cations. The reaction of iodine with N,N'-bis-alkyl-1,4,6,8-naphthalenediimide in chloroform solution have been investigated by spectrophotometric method. The results indicate the formation of two CT-complexes [(DCN1)I]+.I3- and [(DCN2)I]+.I3- at donor:acceptor molar ratio of 1:2. The [(DCN1)I]+.I3- shows the characteristic absorptions of I3- ion at 290 and 360 nm while the charge-transfer transition of [(DCN2)I]+.I3- occurs at 310 nm. Three characteristic bands at the far infrared region in each iodine complex are observed around 135, 105 and 85 cm-1 due to nuas (I-I), nus (I-I) and delta (I3-), respectively with C2v symmetry. The values of the complex formation constant, K, and the absorptivity, epsilon have been calculated.