No abstract

The mechanism of chemiluminescence of 1,2-dioxetane (DO) and 3,3,4,4-tetramethyl-1,2-dioxetane (TMDO) are investigated by the ab initio molecular orbital calculation. The rate-determining step of the chemiluminescent reaction is the O−O bond breaking to form the biradicals. The potential energies along the reaction path are calculated by uB3LYP and uB3P86 methods with 6-31+G(d); the calculated potential barriers are in reasonable agreement with experimental activation energies. An overview of the potential surfaces for overall reaction is obtained. The intersystem crossing mechanism from the singlet biradical to the triplet state is investigated, and the reaction path is followed to the 3(nπ*) excited states of the carbonyl group of respective fragment molecules. The mechanism of promotion to the 1(nπ*) excited state of formaldehyde is investigated by the MCSCF method on DO. The reaction rates and the yield of chemiluminescence are discussed by the RRKM theory of unimolecular reaction.

The shrinking mechanism of comb-type grafted poly(N-isopropylacrylamide) gel due to temperature jump across its volume transition temperature has been investigated. Grafted chains or gel networks were labeled by a dansyl probe, and the temporal change in microenvironment of the dansyllabeled gel was investigated by means of fluorescence spectroscopy. The comb-type grafted poly(Nisopropylacrylamide) gel exhibited a rapid shrinking compared to normal-type NIPA gel, and the change in its microenvironment was found to become hydrophobic more than 10 times faster than normal-type poly(N-isopropylacrylamide) gel by observation of temporal change in the maximum emission wavelength, λ em, of the dansyl group. The freely mobile characteristics of grafted chains are expected to show the rapid dehydration to make tightly packed globules with temperature, followed by the subsequent hydrophobic intermolecular aggregation of dehydrated graft chains. The dehydrated grafted chains created the hydrophobic cores, which enhance the hydrophobic aggregation of the networks.