Further, under the combined action of electron push and pull effects, the C18 unit in NH2-C18-NO2 is slightly positively charged. Due to the very similar but not identical carbon-chain bridges in the molecule, H-C18-H has a small but non-zero dipole moment The above results reveal the occurrence of intramolecular charge transfer in C18 derivatives and suggest their excellent optical properties. And, it appears that the performance of NH2-C18-NO2 may be better. in Figure , it can be observed that the vibration frequencies of the molecules are in the range of 0-2500 cm -1 (i.e., > 4000 nm). Therefore, these C18 derivatives should have excellent IR transparency in the range of 800 to 4000 nm. The orbital analysis shows that the maximum wavelength absorption located in visible region of all molecules are mainly contributed by the electronic transition from their HOMO to LUMO, as shown in the inset in Figure , which accounts for more than 86% of the total.