  Guanine-quadruplex, consisting of several stacked guanine-quartets (GQs), has
emerged as an important category of novel molecular targets with applications
from nanoelectronic devices to anticancer drugs. Incorporation of metal cations
into GQ structure is utilized to form stable G-quadruplexes, while no other
passage has been reported yet. Here we report the room temperature (RT)
molecular self-assembly of extensive metal-free GQ networks on Au(111) surface.
Surface defect induced by an implanted molybdenum atom within Au(111) surface
is used to nucleate and stabilize the cation-free GQ network. Additionally, the
decorated Au(111) surface with 7-armchair graphene nanoribbons (7-AGNRs)
results in more extensive GQ networks by curing the disordered phase nucleated
from Au step edges spatially and chemically. Scanning tunneling
microscopy/spectroscopy (STM/STS) and density functional theory (DFT)
calculations confirm GQ networks' formation and unravel the nucleation and
growth mechanism. This method stimulates cation-free G-quartet network
formation at RT and can lead to stabilizing new emerging molecular
self-assembly.
