  The atomic doping of open-shell nanographenes enables the precise tuning of
their electronic and magnetic state, which is crucial for their promising
potential applications in optoelectronics and spintronics. Among this
intriguing class of molecules, triangulenes stand out with their size-dependent
electronic properties and spin states, which can also be influenced by the
presence of dopant atoms and functional groups. However, the occurrence of
Jahn-Teller distortions in such systems can have a crucial impact on their
total spin and requires further theoretical and experimental investigation. In
this study, we examine the nitrogen-doped aza-triangulene series via a
combination of density functional theory and on-surface synthesis. We identify
a general trend in the calculated spin states of aza-[n]triangulenes of various
sizes, separating them into two symmetry classes, one of which features
molecules that are predicted to undergo Jahn-Teller distortions that reduce
their symmetry and thus their total spin. We link this behavior to the location
of the central nitrogen atom relative to the two underlying carbon sublattices
of the molecules. Consequently, our findings reveal that centrally-doped
aza-triangulenes have one less radical than their undoped counterparts,
irrespective of their predicted symmetry. We follow this by demonstrating the
on-surface synthesis of {\pi}-extended aza-[5]triangulene, a large member of
the higher symmetry class without Jahn-Teller distortions, via a simple
one-step annealing process on Cu(111) and Au(111). Using scanning probe
microscopy and spectroscopy combined with theoretical calculations, we prove
that the molecule is positively charged on the Au(111) substrate, with a
high-spin quintet state of S = 2, the same total spin as undoped neutral
[5]triangulene.
