¿Conjugated? Copolymers from a Pechmann Dye Derivative

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

The 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.

Probing the nature of donor-acceptor effects in conjugated materials: a joint experimental and computational study of model conjugated oligomers

A series of model oligomers consisting of combinations of a traditional strong donor unit (3,4-ethylenedioxythiophene), a traditional strong acceptor unit (benzo[c][1,2,5]thiadiazole), and the ambipolar unit thieno[3,4-b]pyrazine were synthesized via cross-coupling methods. The prepared oligomers include all six possible dimeric combinations in order to characterize the extent and nature of donor-acceptor effects commonly used in the design of conjugated materials, with particular focus on understanding how the inclusion of ambipolar units influences donor-acceptor frameworks. The full oligomeric series was thoroughly investigated via photophysical and electrochemical studies, in parallel with density functional theory (DFT) calculations, in order to correlate the nature and extent of donor-acceptor effects on both frontier orbital energies and the desired narrowing of the HOMO-LUMO energy gap. The corresponding relationships revealed should then provide a deeper understanding of donor-acceptor interactions and their application to conjugated materials.