CONFORMATIONAL-ANALYSIS OF C-60 BALL-AND-CHAIN MOLECULES - A MOLECULAR-ORBITAL STUDY

A computational study of the conformational analysis of a series of C- 60 ball-and-chain bichromophoric molecules (1)-(6) has been carried ou t by means of the AM1 and HF/3-21G//AM1 theoretical methods. It is fou nd that the AM1 method underestimates both the relative conformational energies and the magnitude of the energy barriers separating the fold ed and extended conformers. In contrast, the HF/3-21G//AM1 method give s reasonable values for these quantities. The HF/3-21G//AM1 calculated energy differences between the folded and extended conformers of syst ems (2)-(5) are less than 5 kJ/mol and the barriers to their interconv ersion are c. 30 kJ/mol. The conformational bias in these systems may be modified by the judicious placement of methyl groups in the region of the hydrocarbon chain closest to the C-60 cage. It is found that th e length of the chain and the nature of the non-C-60 chromophore have little effect on the conformational energetics.