We characterise the electronic properties of triangulenes and study their u
se as building blocks in nanotube metallic Y-junctions. We calculate the ba
llistic conductance of such junctions using the Landauer formalism, and ide
ntify the existence of a non-conduction energy window when the system has a
C-3 axis centered on a six-membered ring. Such a system can exploit a loca
l C-6 symmetry to stabilize the central region of the Y-junction, thereby o
pening a band gap. (C) 1999 Elsevier Science B.V. All rights reserved.