Locked energy of axial to equatorial transformation monitored by exciplex and excimer fluorescence

2-O-tert-Butyldimethylsilyl-4,6-bispyrenoyl-myo-inositol-1,3,5-orthoformate (1) and 2-O-tert-butyldimethylsilyl-4-[(4-dimethylamino)benzoyl]-6-pyrenoyl- myo-inositol-1,3,5-orthoacetate (2) adopt unstable chair conformations with five substituents axial, in which the aromatic esters participate in π-stacking, and give excimer and exciplex fluorescence, respectively. Upon addition of acid, the orthoformate/orthoacetate lock is cleaved, which allows the inositol ring to switch to the more stable penta-equatorial chair conformation, with loss of exciplex/excimer fluorescence.