Transformation of Stored Energy into Light in the Chemiluminescence of 1,2-Dioxetanes

Chemiluminescence (CL) is a chemical phenomenon in which stored energy is transformed into light. The stored energy in a CL system must be sufficient to generate electronically excited carbonyl products. Rapid transfer of the heat of reaction is required to produce CL. However, this transformation of heat into light has not been demonstrated by correlating the reaction energies available with the light energies produced. We addressed this problem by re-evaluating the reactions of a series of 1,2-dioxetanes by making calorimetric measurements of heats of reaction and transformation efficiencies (phi(ET)), and compared the results with quantum yields (phi(CL)) of CL reactions. Our results provide experimental support that the phi(ET) values of the 1,2-dioxetanes were essentially the same as their phi(CL) values. Additionally, we addressed the even-odd (meta-para) substitution issue through discussion of the heats of reaction of 1m (3-(2-spiroa-damantane)-4-methoxy-4-(3"-tert-butyldimethylsilyloxy)phenyl-1,2-dioxetane) and 1p (3-(2-spiroadamantane)-4-methoxy-4-(4-tert-butyldimethyl-silyloxy)-phenyl-1,2-dioxetane) with the aid of empirical calculations and kinetic studies. We found that 1m(-) provides sufficient stored energy to give the emitter 5m(-)* while the energy level of emitter 5p(-)* is higher than the stored energy of 1p(-). Thus, the transition energy of 1m(-) is higher than that of 1p(-). The even-odd substitution effect therefore was manifested as different degrees of stored energy and transition-state energy.