Azulene-Fused Linear Polycyclic Aromatic Hydrocarbons with Small Bandgap, High Stability, and Reversible Stimuli Responsiveness

Azulene-fused polycyclic aromatic
hydrocarbons (PAHs) were synthesized
from commercially available azulene in four steps. The resulting azulene
conjugates exhibited significantly narrow HOMO–LUMO bandgaps
with high air stability, confirmed by photophysical study. Introduction
of azulene also enabled the unique reversible stimuli-responsiveness
even with the weak acid and base, which can potentially control the
degree of conjugation and optoelectronic properties by simple acid–base
and redox processes.