Chemiluminescence in visible and infrared spectral regions and quantum chain reactions upon thermal and photochemical decomposition of adamantylideneadamantane-1,2-dioxetane in the presence of chelates Pr(dpm) 3 and Pr(fod) 3

Abstract

Catalysis of adamantylideneadamantane-1,2-dioxetane (AAD) decomposition in the presence of chelates Pr(fod) 3 or Pr(dpm) 3 proceeds through the formation of the complex AAD·Pr(fod) 3 or AAD·Pr(dpm) 3, respectively. The rate constants ( k 2) of AAD decomposition in the AAD·Pr(fod) 3 complex and stability constants ( K) of the complex have been determined by the chemiluminescence method. The Arrhenius parameters of AAD decomposition in AAD·Pr(fod) 3 (lg A = 12 ± 1.2 and E a = 26 ± 3 kcal mol −1) and thermodynamical parameters of the formation of AAD·Pr(fod) 3 (Δ H = 7.6 ± 2.8 kcal mol −1 and Δ S = 29 ± 10 kcal degree mol −1) have been calculated from the temperature dependencies of k 2 and K. In the case of Pr(dpm) 3 the parameters K and k 2 could not be obtained since the complex decomposed at the conditions of kinetical experiments, although an estimation of the activation energy of AAD·Pr(dpm) 3 decomposition gave E a = 25 ± 2 kcal mol −1. Upon decomposition of AAD·Pr(fod) 3 or AAD·Pr(dpm) 3 excitation of Pr 3+ occurs. In the case of AAD·Pr(fod) 3 the efficiency of excitation was estimated to be φ Pr ∗ ≤ 10%. The reaction is accompanied by chemiluminescence in visible and infrared regions due to radiative transitions from 3 P 1 , 3 P 0 and 1 D 2 levels of Pr 3+. Photochemical decomposition of AAD initiated by Pr(fod) 3* is accompanied by quantum chain reaction, the quantum yield of photolysis is φ max = 3.6 ± 1.2 mol Einstein −1. The branched quantum chain reaction is observed on thermal decomposition of AAD in the presence of an excess amount of Pr(fod) 3. Branching of the chain may be realized through the quenching of Pr(fod) 3 * where Pr 3+ is in the 3 P 0 or 3 P 1 - excited states by the AAD·Pr(fod) 3 complex with the preservation of excitation energy of Pr 3+ in lower lying 1 D 2 -state. Energy transfer on the Pr(fod) 3·AAD complex results in the decomposition of AAD with excitation of Pr 3+ into 3 P 1 , 3 P 0 or 1 D 2 state.