Theoretical studies on the chromogenic mechanism of 1,3-N,N '-bis-4-(4 '-nitrobenzenediazo)phenylsquaraine with fluorinion

Based on the AM1 studies of the electronic structure of 1,3-N,N'-bis-4-(4'- nitro benzenediazo) phenyl squaraine (BNBPS), the interacting model in whic h a fluorinion approaches vertically the planar four - member ring of BNBPS has been proposed and the stable geometry of [ BNBPS - F](-) has been foun d. The chromogenic mechanism has been suggested in terms of the calculated total energies of BNBPS and [BNBPS - F](-) at ground and first excited stat es, respectively. The interactions between BNBPS and Cl-, Br-, I- have also been calculated and the results are in agreement with the experimental phe nomena.