4nπ Stable Multitasking Azapentacene: Acidochromism, Hole Mobility, and Visible Light Photoresponse

Herein, we describe the synthesis, characterization,
and optoelectronic
investigation of a stable 4nπ dihydrotetraazapentacene derivative.
The neutral dihydrotetraazapentacene contains a 24π-conjugated N-heteroacene core with two phenyl pendants appended thereof.
The exceptional stability of this formally antiaromatic π-system
is attributed to the fused dihydropyrazine ring, which has ethenamine
(enamine) conjugations, and hence, the π-electrons delocalize
over the nearly planar azapentacene core to endow with a global aromatic
characteristic. The embedded dihydropyrazine also offers an additional
Clar’s sextet with enhanced aromaticity. The present dihydrotetraazapentacene
can be considered as a multitasking N-heteroacene,
which showed photoresponsive nature under visible light illumination,
acidochromism in solution, and p-type charge transport with an appreciable
field-effect hole mobility of 0.02 cm2 V–1 s–1 and a bulk p-type mobility of 0.98 ×
10–4 cm2 V–1 s–1 in the space charge-limited regime of operation measured
in the hole-only device. Nucleus-independent chemical shift calculation,
anisotropy of the induced current density plot, and anisotropic mobility
calculation were performed to support the experimental findings.