The synthesis of 4-phenyl-4H-arsolo[2,3-d:5,4-d′]bis(thiazole)
is reported,
and its properties are compared to those of the previously prepared
phosphole analogue. By comparison of their single-crystal structures,
the harmonic oscillator model of heterocyclic electron delocalization
(HOMHED) was used to directly compare the aromatic character of the
two systems. The findings demonstrate that, although both compounds
can be considered aromatic, the phosphole-containing compound had
a greater degree of aromatic character than its arsole analogue. The
arsole derivative exhibited excellent stability in ambient air with
no formation of the arsole oxide observed upon storage. The absorption
and photoluminescence spectra of the arsole derivate were subtly altered
in comparison to the phosphole derivative, suggesting that changing
pnictogenic atoms in such fused-ring systems to heavier analogues
could be a viable way of tuning both the ambient stability and optoelectronic
properties of such materials.