Synthesis, structure and electronic transport properties of phenanthrenone derivatives

Abstract

Phenanthrenone 1 was synthesized via cyclization of 4,5-dibromo-9-fluorenone with diarylacetylenes, followed by selective reduction of the carbonyl group to yield hydroxyl derivative 2 and methylene derivative 3, alongside reference molecule 4. UV-vis absorption spectroscopy revealed that compound 3 exhibits a blueshift (λ_max = 257 nm) compared to compound 1 (λ_max = 264 nm) due to the disruption of conjugation by the methylene group, while compound 2 (λ_max = 267 nm) shows a redshift compared to compound 3, attributed to the electron-donating effect of the hydroxyl group. Single-molecule conductance measurements using the STM-BJ technique demonstrated a 2-fold difference between 1 (10^{−4.37±0.01}G₀) and 3 (10^{−4.67±0.01}G₀), attributed to the carbonyl group's ability to lower the HOMO–LUMO gap and enhance charge transport. Notably, cyclization at the 4,5-positions has a limited impact on conductance, as evidenced by the small differences between 1 (10^{−4.37±0.01}G₀), 2 (10^{−4.63±0.01}G₀), and 4 (10^{−4.50±0.01}G₀). These results indicate that functional group modifications and skeletal cyclization both influence the electronic properties of phenanthrenone derivatives, with functional group modifications playing a more noticeable role in modulating conductance. This work provides a framework for designing functional organic molecules with tailored electronic properties, advancing the development of next-generation nanoscale electronic devices.