Redox- and Protonation-Tunable Diboraheptacenes.

Area of Science:

• Organic Chemistry
• Materials Science
• Supramolecular Chemistry

Background:

• Acenes are key organic electronic materials due to their π-electron delocalization and small HOMO-LUMO gaps.
• Incorporating heteroatoms into acenes allows tuning of electronic properties and introduces sites for chemical reactions.
• The redox chemistry of boron-doped higher acenes is not well understood.

Purpose of the Study:

• To synthesize and characterize diboraheptacenes.
• To investigate the multistate redox and protonation chemistry of these novel compounds.
• To establish the relationship between redox/protonation states and their electronic/photophysical properties.

Main Methods:

• Synthesis of tetrahydrodiboraheptacene (1).
• Generation of radical anion (1•−) via one-electron reduction.
• Accessing fully aromatized diborataheptacene dianion (22−) via double deprotonation.
• Characterization of redox-interconversion between benzenoid and quinoidal structures.
• Spectroscopic analysis (UV-Vis, fluorescence) of dianion (22−) and neutral species (2).
• Investigating reactivity with CO2, acrylonitrile, and H2O.

Main Results:

• Synthesis and structural characterization of diboraheptacene derivatives.
• Generation of radical anion and dianion species with distinct redox states.
• Demonstration of redox-interconversion between benzenoid and quinoidal structures (22− to 2).
• Diborataheptacene dianion (22−) exhibits NIR absorption (λabs = 951 nm) due to a small HOMO-LUMO gap.
• Neutral diboraheptacene (2) displays red fluorescence (λem = 682 nm).
• Dianion undergoes cycloaddition reactions and hydroxylation.

Conclusions:

• Diboraheptacenes represent the first diboron-doped π-isosteres of all-hydrocarbon heptacene.
• Redox and protonation state significantly influence electronic structure, photophysics, and reactivity.
• These findings establish an extended diboraacene platform with tunable properties for organic electronics.