Electron-Donating and Electron-Withdrawing Subunit Effects on Coumarin-BODIPY Dyads: Optical and Electrochemical Properties and Molecular Interactions

In this study, a series of coumarin-BODIPY molecules were synthesized using a Sonogashira cross-linking reaction. The effects of electron withdrawing and electron donating moieties on electrochemical and optical properties were supported by results of density functional theory calculations, and energy transfer mechanisms were investigated. The band gap value decreased from 2.0 eV to 1.6 eV due to reversible oxidation of the extra dimethylamino subunit at lower potential. Besides, characteristics of the crystal structures were investigated with single-crystal X-ray diffraction, and crystallinity was supported by differential scanning calorimetry. In addition, when the thin film surface morphologies were examined, it was clearly observed that the N,N-dimethylamino group on the coumarin-BODIPY dyad (B3) formed large-scale domains due to its crystalline behavior. As a result, Forster-type energy transfer was observed for coumarin-BODIPY dyads containing different electron withdrawing and donating subunits.