Dynamic surfaces: The conformational transition of 2,6-bis(1-aryl-1,2,3-triazol-4-yl)pyridine (BTP) derivatives, triggered by a change in pH, has been observed with a sub-nm resolution by STM at the solid-liquid interface. Upon addition of trifluoroacetic acid two different BTP molecules, each forming a highly ordered physisorbed monolayer, underwent significant conformational changes from their "rosette" to their "tetragon" forms, as reflected in dramatically altered 2D self-assembly over large areas extending over hundreds of nanometers (see graphic).