  We study spin excitations and Kondo effect in open-shell nanographenes,
motivated by recent scanning tunneling inelastic spectroscopy experiments.
Specifically, we consider three systems, the triangulene, the extended
triangulene with rocket shape, both with an $S=1$ ground state, and a
triangulene dimer with $S=0$ on account of intermolecular exchange. We focus on
the consequences of hybridization of the nanographene zero-modes with a
conducting substrate on the $dI/dV$ lineshapes associated with spin
excitations. The partially filled nanographene zero-modes coupled to the
conduction electrons in the substrate constitute multi-orbital Anderson
impurity models that we solve in the one-crossing approximation which treats
the coupling to the substrate to infinite order. We find that the coupling to
the substrate leads to (i) renormalization of the spin flip excitation energies
of the bare molecule, (ii) broadening of the spectral features and (iii) the
emergence of zero bias Kondo peaks for the $S=1$ ground states. The calculated
substrate induced shift of the spin excitation energies is found to be
significantly larger than their broadening, which implies that this effect has
to be considered when comparing experimental results and theory.
