Electronic structure tunability of carbon-based 1D-polymers combining cross-conjugation and nitrogen doping

Abstract

Quasi-one-dimensional polymer structures with extended π-electron systems stand out due to their remarkable application in light-emitting diodes and devices. Upon smart choice of their building units, such carbon-based organic nanoarchitectures provide excellent optoelectronic properties by tuning their dimensionality, atomic structure or intrinsic doping. Here, we generate and study three canonical cross-conjugated quasi one-dimensional chains with controlled nitrogen intrinsic doping, which is selectively introduced into their poly-phenylene backbones. By means of scanning tunneling microscopy and spectroscopy we corroborate that the cross-conjugation that break the chain linearity is exclusively responsible of the electronic confinement in the straight segments. Moreover, we demonstrate that the LUMO state exhibits similar spatial distribution for the cross-conjugated polymers independently of the pyridine content of the initial precursor. Despite this coincidence, the semiconducting character and other relevant electronic properties of the polymers are found to depend both on the chain morphology and on the precise position and number of doping nitrogen atoms synthetically introduced into the molecular precursors. We compare these results to related previous studies, which allows us to unambiguously validate the opto-electronic tunability upon the choice of the polymers’ building units.