Fig. 4: On-surface synthesis of tetraazaundecacene 3 via STM tip-induced cleavage of the ethano protecting groups of 5 and electronic characterization.
From: On-surface synthesis and characterization of nitrogen-substituted undecacenes
a Successive STM topography images illustrating the cleavage process. Top image shows a cluster of 5 (leftmost molecule has already one bridge cleaved) with blue crosses indicating the locations where the voltage pulse is applied. Middle image shows the intermediate state after two voltage pulses, and bottom image shows the final result after applying a voltage pulse to all the molecules of the cluster. Scale bars: 5 nm. b DFT-calculated equilibrium geometry of a cluster of five molecules of 3. Red ovals indicate hydrogen bonds. The side view is shown for a single molecule in the direction indicated by the green arrow. c Experimental constant-height dI/dV maps of the frontier states for a cluster of five tetraazaundecacene molecules. PIR−1, PIR, and NIR stand for the second positive, the positive, and the negative ion resonances, respectively. Each map includes a zoom-in of a single molecule indicated by the green rectangle. Scale bars: 1 nm. d, e DFT-calculated molecular orbitals (α, β denote the two spin channels) and LDOS mappings at height 5 Å for the broken-symmetry open-shell singlet and the closed-shell state, respectively. Scale bars: 1 nm.
