We have investigated acid- and base-induced conformational alterations of N-aryl-N-troponyl amides containing an electron-donating group on the phenyl ring. NMR spectral studies indicated that the E/Z conformational preferences of these amides can be reversibly controlled by pH-dependent protonation or deprotonation of the tropolone moiety. Thus, these compounds have potential applications as acid/base-controllable molecular switches.