Asphaltene molecular size and structure

The rotational correlation times of individual asphaltene molecules have be en determined using fluorescence depolarization techniques, addressing an a ctive, long-standing controversy. Using simple theoretical models and using model-independent comparisons with known chromophores, a range of asphalte ne molecular diameters is obtained of 10-20 Angstrom. Comparison with corre sponding data of known chromophores indicates a molecular mass for asphalte ne molecules of 500-1000 amu. Furthermore, we have performed the first dire ct measurement correlating molecular size with constituent chromophore size ; we establish that the bulk of asphaltene molecules possess 1 or 2 (aromat ic) chromophores per molecule. Similar results are found for the largest ar omatic molecules of the de-asphaltened crude oil.