Donor–Acceptor–Donor Triads with Flexible Spacers: Deciphering Complex Photophysics for Targeted Materials Design

Abstract

AbstractThe complex photokinetics of donor–acceptor–donor triads with varying flexible spacer lengths (n = 4–10 carbon atoms) are investigated in liquid and solid solution, as well as in crystals, by steady‐state and transient fluorescence spectroscopy combined with computational studies. For the short spacer (n = 4) in a liquid solution, dynamic charge‐transfer (CT) state formation with subsequent, efficient exciplex emission is observed, effectively competing with quenching through electron transfer (eT) via a radical ion pair. In a solid solution, a fluorescent CT static complex is formed upon freezing for all spacer lengths. This allows the observations of a former seminal report on stimuli‐responsive high‐contrast fluorescence on/off switching in films of the triads to be reassigned (Adv. Mater. 2012, 24, 5487), now providing a holistic picture on varying spacer length. In fact, external stimuli of the film by modulating the geometry of the CT complex, which results in on/off fluorescence switching (for n > 4) or in a change of the emission color (n = 4). The work thus demonstrates how in‐depth analysis of complex photophysics can be put to practical use in materials science.