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　(λmax　=　257　nm)　compared　to　compound　1　(λmax　=　264　nm)　due　to　the　disruption　of　conjugation　by　the　methylene　group,　while　compound　2　(λmax　=　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±0.01G0)　and　3　(10−4.67±0.01G0),　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±0.01G0),　2　(10−4.63±0.01G0),　and　4　(10−4.50±0.01G0).　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.　©　2025　The　Royal　Society　of　Chemistry.