Bandgap Engineering in π‑Extended Pyrroles. A Modular Approach to Electron-Deficient Chromophores with Multi-Redox Activity

A family
of bandgap-tunable pyrroles structurally related to rylene
dyes was computationally designed and prepared using robust, easily
scalable chemistry. These pyrroles show highly variable fluorescence
properties and can be used as building blocks for the synthesis of
electron-deficient oligopyrroles. The latter application is demonstrated
through the development of π-extended porphyrins containing
naphthalenediamide or naphthalenediimide units. These new macrocycles
exhibit simultaneously tunable visible and near-IR absorptions, an
ability to accept up to 8 electrons via electrochemical reduction,
and high internal molecular free volumes. When chemically reduced
under inert conditions, the most electron-deficient of these macrocycles
revealed reversible formation of eight charged states, characterized
by remarkably red-shifted optical absorptions, extending beyond 2200
nm. Such features make these oligopyrroles of interest as functional
chromophores, charge-storage materials, and tectons for crystal engineering.