The two-step nucleation model for crystal nuclei formation explains several experimental and theoretical results better than the classical nucleation theory. We report here direct visualization of the two-step nucleation model for organic molecular crystallization. Evaporative crystallization from a solution of a dibenzoylmethane boron complex that displays mechanofluorochromism, a fluorescence color change induced by mechanical perturbation, was probed by fluorescence change. The dependence of fluorescence change on dispersion concentration of the complex in a polymer matrix was also investigated. We detected transitional emission from the amorphous cluster state prior to crystallization. This is the first demonstration of the two-step nucleation model based on fluorescence color changes.
The effect of the solvent viscosity dependence of time-resolved magnetoluminescence (ML) on the delayed fluorescence of 9,10-diphenylanthracene (DPA) sensitized by platinum octaethylporphyrin has clarified the structure and dynamics of the triplet-triplet pair (TT), i.e., the transition state of triplet fusion. Phase inversion of the ML effect with time provides evidence for the recycle dynamics of the excited triplet state for DPA in triplet fusion. The electron spin-relaxation by random molecular rotation causes intersystem crossing among the different spin states of the triplet-triplet pair and allows the (3,5)TT to engage in triplet fusion. Therefore, slow-down of the molecular diffusion by an increase in the solvent viscosity can enhance the triplet fusion yield. However, the reduction of the ML effect observed in quite high viscosity solvents suggests that the substantially slow rotational motion decreases the triplet fusion yield due to steric factors in electron exchange from the triplet-triplet pair.
Living metathesis polymerization of [o- (trifluoromethyl)phenyl] acetylene, a phenylacetylene with an electron-withdrawing group, has been achieved by using molybdenum-based three-component catalysts. Thus polymerization by MoOCWt-BuiSn-EtOH (1:1:0.5 mole ratio) catalyst in toluene at 30 °C produced a polymer having a narrow molecular weight distribution; MjMa = 1.06. Upon three consecutive additions of fresh monomer feeds to completely polymerized systems, the M" of the polymer increased in direct proportion to monomer conversion, while the MjM" remained < 1.1. The initiator efficiency was ca. 0.10. The M0CI5n-ButSn-EtOH (1:1:0.5) catalyst also induced living polymerization, though the MJMn (ca. 1.20) was somewhat larger. Effects of catalyst components and polymerization conditions have been studied.
New catalyst systems composed of MoCl5 (or MoOC14), Bw4Sn, and ethanol (molar ratio 1 : 1 : 0.5) effect living polymerisations of 1 -chloro-oct-1 -yne and o-(trimethylsilyl)phenylethyne, which are the first examples of living polymerisation of acetylenes.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.