Tuning Excited-State Charge Transfer Character in Cofacial Core-Substituted Perylenediimide Dimers
Samuel B Tyndall1, Jonathan R Palmer1, Nikolai A Tcyrulnikov1
1Department of Chemistry and Paula M. Trienens Institute for Sustainability and Energy, Northwestern University, Evanston, Illinois 60208-3113, United States.
Abstract:
Understanding the interplay between excimer formation and symmetry-breaking charge separation is important for optimizing charge separation in organic photovoltaic materials. To explore this connection, we synthesized four 1,6,7,12-tetrakis(p-X-phenoxy)perylene-(3,4:9,10)-bisdicarboximide cofacially stacked dimers, where X = MeO, tert-butyl, Br, and CF3. Steady-state spectroscopy reveals H-type aggregation and excimer formation in all four dimers, while transient absorption spectroscopy shows relatively small changes in their excited-state absorptions. However, time-resolved fluorescence (TRF) spectroscopy shows that relaxation occurs from an initial Frenkel exciton-dominated excimer state to one in which charge transfer (CT) character contributes. Relaxation to the lower-lying state with CT character is attributed to a combination of structural and charge distribution changes elicited by varying the substituents. This study illustrates how subtle changes in charge distribution and structure can combine to influence the excited state dynamics that influence charge separation in molecular dimers.
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