Understanding and tuning photogenerated excitons in organic materials are crucial for high performance organic photovoltaics. Using a combined experimental and computational approach, we designed seven triphenylamine-based molecules to generate excitons with a size range of 2.0-8.6 angstrom. The absorption and fluorescence wavelengths of the molecules increase quadratically with the size of excitons generated while the fluorescence emission lifetime shows a volcano plot. The charge separated excitons were identified with a decay lifetime of about 200 ps. This work opens up a new way of studying organic supramolecules, polymers, and bulk materials for efficient organic photovoltaics and photocatalysis. (C) 2014 Elsevier B.V. All rights reserved.