105906-41-0Relevant academic research and scientific papers
Substituent Effects upon Efficiency of Excited-State Acetophenones Produced on Thermolysis of 3,4-Diaryl-3,4-dimethyl-1,2-dioxetanes
Richardson, William H.,Stiggal-Estberg, Diana L.,Chen, Zhangping,Baker, John C.,Burns, David M.,Sherman, David G.
, p. 3143 - 3150 (2007/10/02)
The effects of meta and para substituents upon the triplet (αT) and singlet (αS) efficiencies in the thermolysis of 3,4-diaryl-3,4-dimethyl-1,2-dioxetanes 3, 3-aryl-3,4,4-trimethyl-1,2-dioxetanes 4, and 3-aryl-3-(bromomethyl)-4,4-dimethyl-1,2-dioxetanes 5 are reported.Triplet efficiencies for series 3 dioxetanes, where the two proketone moieties are identical, are sensitive to aryl substituent changes.Attempted correlation of log αT with Hammett-type substituents constants failed, and the best correlation of log αT was with the lowest triplet energy of the acetophenones T) = (0.77+/-0.19)ET1(ArCOCH3)-55.05+/-14.00, r=0.834, Sy*x=+/-0.336>.This type of correlation was previously observed with 3-aryl-3-methyl- and 3-aryl-3-methyl-3,3-(2,2'-biphenyldiyl)-1,2-dioxetanes, where the slopes (S values) are 0.38+/-0.14 and 0.52+/-0.08, respectively.In these two dioxetane series, the triplet energies of the companion proketones (formaldehyde and fluorenone) to ArCOCH3 are approximately equal to and less than ET1(ArCOCH3).For the 4 and 5 series dioxetanes, there was no change in triplet efficiency with various aryl substituents, where the average αT values are 29.1+/-2.4percent for 4 and 28.1+/- 0.7percent for 5.For these two dioxetane series, the triplet energy of the companion proketone (acetone) is higher than ET1(ArCOCH3).With regard to triplet efficiencies, all of these dioxetane series fall into two categories: (i) where the companion proketones possess triplet energies approximately equal to or less than ET1(ArCOCH3) and where αT is dependent upon substituent changes in the ArCOCH3 moiety; (ii) where the companion proketone possesses a triplet energy higher than ET1(ArCOCH3) and αT is independent of substitution changes in the ArCOCH3 moiety.An exciplex or encounter complex process is proposed to explain the apparent communication between the two proketone moieties in category i dioxetanes.Activation parameters for series 3-5 were typical of most other tetrasubstituted dioxetanes.The ρ values for ?+ correlations of series 3 and 4 plus 5 dioxetanes are -0.285 +/- 0.033 and -0.20 +/- 0.05, respectively, which is consistent with a 1,4-dioxy biradical decomposition process.
