Spectrophotometric study of molecular complex formation of asphaltene with two isomeric chloranils

Coal derived asphaltene has been observed spectrophotometrically to form molecular complexes of charge transfer type with o- and p-chloranils. The CT absorption peaks have been detected by difference spectral method and the wavelengths of the CT peaks are in the expected order of electron affinities of the chloranils. The formation constants (K) have been determined using the Benesi-Hildebrand equation. The magnitudes of K are large compared to those of weak charge transfer complexes (for which K≈101-103 dm3 mol−1) but are comparable to those of some recently reported supramolecular or inclusion complexes. The study reveals the presence of π-donor (i.e. aromatic) type of compounds in asphaltene molecule. It also supports the view that asphaltene molecules exist in solution forming micellar aggregate, in the cavities of which the chloranil molecules are included.