Modulating　charge　accumulation　in　molecular　structures　to　switch　the　quantum　interference　effect　(QIE)　presents　a　promising　approach　for　manipulating　conductance　in　molecular　devices　without　altering　the　molecular　structure,　which　is　crucial　for　real　molecular　device　applications.　However,　understanding　the　QIE　switch　by　charging　is　still　a　challenge.　In　this　study,　we　used　carbon　ring　structures　to　induce　and　finely　modulate　the　charge　accumulation　in　cross-conjugated　diphenylpenta-1,4-dien-3-one　molecular　junctions.　Our　measurements　show　that　an　approximate　one-order　magnitude　conductance　suppression　was　detected　in　the　highly　charged　structure　compared　to　the　moderately　charged　structures　by　using　the　scanning　tunneling　microscopy　break　junction　(STM-BJ)　technique.　The　theoretical　calculations　revealed　that　the　energy　of　anti-resonance　in　destructive　QI　was　governed　by　the　ratio　of　orbital　coefficients　between　HOMO−1　and　HOMO.　Specifically,　a　higher　ratio　shifted　the　anti-resonance　toward　the　HOMO,　whereas　a　lower　ratio　maintained　the　anti-resonance　around　the　Fermi　energy.　The　charge　accumulation　within　the　conjugated　structure　decreased　the　coefficient　ratio,　thereby　switching　the　QIE　from　constructive　to　destructive　when　the　number　of　ring　members　reached　seven.　This　study　not　only　provides　a　chance　to　understand　the　mechanism　of　QIE　switching　by　charge　but　also　paves　the　way　for　utilizing　the　charge　accumulation　to　manipulate　the　conductance　switch　in　molecular　devices.　©　2025　The　Royal　Society　of　Chemistry.