Multifaceted
Regioregular Oligo(thieno[3,4‑<i>b</i>]thiophene)s
Enabled by Tunable Quinoidization and Reduced
Energy Band Gap
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Abstract
Thiophene-based
materials have occupied a crucial position in the
development of organic electronics. However, the energy band gaps
of oligo- and polythiophenes are difficult to modulate without resorting
to push–pull electronic effects. We describe herein a new series
of monodisperse oligo(thieno[3,4-<i>b</i>]thiophene) derivatives
with well-defined regioregular structures synthesized efficiently
by direct C–H arylation. These compounds show a unique palette
of colors and amphoteric redox properties with widely tunable energy
band gaps. The capacity to stabilize both cations and anions results
in both anodic and cathodic electrochromism. Under excitation, these
compounds can produce photoionized states able to interconvert into
neutral triplet or form these through singlet exciton fission or intersystem
crossing. These features arise from a progressive increase in quinoidization
on a fully planar platform making the largest effective conjugation
length among hetero-oligomers. Oligo(thieno[3,4-<i>b</i>]thiophene)s might represent the more distinctive family of oligothiophenes
of this decade