The origin of the fluorescence redshift during asphaltene aggregation remains debated due to the great diversity of asphaltene molecules, while the extended Frenkel exciton model provided a theoretical framework for studying multi-chromophore systems such as asphaltene aggregates. We investigated the fluorescence energy of hundreds of asphaltene dimers based on 132 experimentally determined asphaltene monomer structures. Our result shows that the dimer’s fluorescence energy is always lower than both of its monomers regardless of its intermolecular conformation, with its redshift dominated by superexchange. The dimer oscillator strength predominantly depends on the monomer with the lower fluorescence energy, and the involvement of charge-transfer states and the cancellation between monomer transition dipole moments suppressed the fluorescence especially when two monomers have similar fluorescence energy. The above findings hold for all asphaltene dimers despite their diversity, which offers a theoretical interpretation for comprehending the relationship between asphaltene aggregation and its fluorescence variation. Furthermore, this work provides theoretical insights into other research areas related to organic planar conjugated systems with multiple chromophores.
See the supplementary material for detailed information on the asphaltene monomers, the change in angle between monomer TDMs after dimer structure optimization, comparison of DFT functionals, estimation of BSSE, S1 and diabatic state energy and excited state EDA result for the different conformers of the rotated C22-PC113 and C05-C22 dimers, monomer ID used in Figure 7 and Figure 8, energy and excited state EDA for the TDM-perpendicular C22-X series, S1 composition analysis for the TDM-perpendicular C22-X series, monomer ID used in Figure 9 and Figure 10, and results for excited state EDA and S1 composition analysis of 496 coal asphaltene dimers
The constructed structures of all 132 asphaltenes (ZIP).