Dioxetane scission products unchanged by mechanical force.

Dioxetane-based force-induced light emission from polymers, or mechanoluminescence, is a powerful new way of characterizing the behavior of polymeric materials under stress. Here, we reveal that breaking the dioxetane mechanically gives strikingly similar products to those formed on thermal activation, with a singlet/triplet ratio of 1:9.9 and a total quantum yield of 9.8%. A sensitized relay scheme ensured high reproducibility in the detection of the short-lived triplet products. In addition to guiding the design of more sensitive mechanoluminescent probes, the similarity in the scission products indicates that once mechanical force releases the steric lock between the adamantyl groups, the dioxetane undergoes scission in a pathway that resembles the thermal process. Excited states are formed only after the main transition state in a region in which the excited- and ground-state surfaces are nearly degenerate, which, thus, accounts for the remarkable similarity in the scission products.