Novel Zwitterionic Diallylzirconium Complexes: Synthesis, Structure, Polymerization Activity, and Deactivation Pathways

Abstract

Without interstate mixing the conjugate does not function as a phototropic assembly, and absorbed photons are converted into heat within about 50 ps.Interstate mixing extends the overall timescale for charge recombination to about 40 µs, but the phototropic process itself continues for milliseconds.This is because diffusional charge recombination occurs between separated π radical cations, and is followed by slower reinsertion of the dication into the receptor (see Figure 1).In contrast to the case with MV•2PF 6 , where the acceptor is nonfluorescent and separation of the RIP is minimal, formation of free DAP•2PF 6 as a transitory species can be followed by fluorescence spectroscopy using two-color (or delayed pulse) excitation.Background fluorescence, being set by the amount of free DAP•2PF 6 , can be suppressed with excess CE10, while the rate of reinsertion of DAP•2PF 6 into the cavity is solvent-dependent.Similar behavior is found for ADIQ•2PF 6 , but the level of background fluorescence is too high for practical application.With complex 1, however, laser-induced fluorescence selectively tracks the evolution and disappearance of free diazapyrenium dications. Experimental Section DAP•2PF6[11] and CE10 [17] were prepared by literature methods.ADIQ•2PF6 was available from earlier work [11].All compounds gave satisfactory analytical data that were consistent with their assigned structures.Fast kinetic measurements were made with nanosecond and sub-picosecond laser flash photolysis equipment, built for this purpose, similar to that described previously [11].The excitation wavelength was 440 nm.Decay kinetics were obtained by collecting transient differential absorption spectral profiles at about 50 delay times.Binding constants were determined by fluorescence spectroscopy with about 50 different concentrations of crown ether being added to a solution of fluorophore in acetonitrile.X-ray structure analysis of 1: C48H54F12N3O10P2, Mr = 1122.88,yellow prisms, 0.15 × 0.20 × 0.45mm, measured at 293(2) K; triclinic, P1, a = 11.284(2),b = 11.211(2),c = 12.043(2) Å, α = 99.95(3),β = 106.28(3),γ = 107.15(3)°,V = 1342(4) Å 3 .ρcalcd = 1.389 mgm -3 , Enraf-Nonius CAD-4 diffractometer, MoKα radiation (λ = 0.71069 Å), µ = 0.179 mm -1 , ω/2θ scan, 2θ ≤ 60°; of 7524 reflections measured, 6509 were independent; ψ-scan absorption correction, Tmin = 0.94, Tmax = 1.00.The structure was solved with direct methods (SHELXS-86), and refined on F 2 (SHELXL-93; non-hydrogen atoms, except disordered F atoms, were refined anisotropically, and H atoms at calculated positions in riding mode).R1 = 0.0959 for 6494 reflections (F0 ≥ 4σ(F)), wR2 = 0.2949 for all data, GOF = 1.0086, 330 parameters.∆ρmax = 1.042 eÅ -3 in the vicinity of a severely disordered solvent molecule.