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Strongelectron correlation within a quasi-spin model of chromophoreswas recently shown to enhance exciton energy transfer significantly.Here we investigate how the modulation of the electronic structureof the chromophores by chemical substitution can enhance energy-transferefficiency. Unlike previous work that does not consider the directeffect of the electronic structure on exciton dynamics, we add chemicalsubstituents to the fluorone dimer to study the effect of electron-donatingand electron-withdrawing substituents on exciton energy transfer.The exciton dynamics are studied from the solution of a quantum Liouvilleequation for an open system whose model Hamiltonian is derived fromexcited-state electronic structure calculations. Both van der Waalsenergies and coupling energies, arising from the Hellmann–Feynmanforce generated upon transferring the dimers from infinity to a finiteseparation, are built into the model Hamiltonian. Though these twoeffects are implicitly treated in dipole-based models, their explicitand separate treatment as discussed here is critical to forging thecorrect connection with the electronic structure calculations. Wefind that the addition of electron-donating substituents to the fluoronesystem results in an increase in exciton-transfer rates by factorsranging from 1.3–1.9. The computed oscillator strength is consistentwith the recent experimental results on a larger heterodimer systemcontaining fluorone. The oscillator strength increases with the additionof electron-donating substituents. Our results indicate that the studyof chromophore networks via electronic structure will help in thefuture design of efficient synthetic light-harvesting systems. [ABSTRACT FROM AUTHOR]