ABSTRACT
A series of luminescent, neutral pentacoordinate dithieno[3,2-b:2',3'-d]phosphole compounds was synthesized by [4+1] cycloaddition of o-quinones with the corresponding trivalent phospholes. The electronic and geometrical modification of the π-conjugated scaffold implemented here impacts the aggregation behavior of the species in solution. It proved successful in generating species with improved Lewis acidity of the phosphorus center that was then leveraged for small-molecule activation. Hydride abstraction from an external substrate involving the hypervalent species is followed by an intriguing P-mediated umpolung from the hydride to a proton and supports the catalytic potential of this class of main-group Lewis acids for organic chemistry. This study is a comprehensive investigation into various methods, including electronic, chemical, geometric modifications (and sometimes combinations of these approaches) to systematically improve the Lewis acidity of neutral and stable main-group Lewis acids with practical value for a range of chemical transformations.
Subject(s)
Chemistry, Organic , Lewis Acids , Catalysis , Concept Formation , Cycloaddition ReactionABSTRACT
Nanoparticle (NP) embedded conductive polymer films are desirable platforms for electrocatalysis as well as biomedical and analytical applications. Increased catalytic and analytical performance is accompanied by concomitant decreases in NP size. Herein, highly reproducible electrogeneration of low dispersity Au nanocluster embedded ultra-thin (â¼2 nm) conductive polymer films at a micro liquid|liquid interface is demonstrated. Confinement at a micropipette tip facilitates a heterogeneous electron transfer process across the interface between two immiscible electrolyte solutions (ITIES), between KAuCl4(aq) and a dithiafulvenyl-substituted pyrene monomer, 4,5-didecoxy-1,8-bis(dithiafulven-6-yl)pyrene (bis(DTF)pyrene), in oil, i.e., a w|o interface. At a large ITIES the reaction is spontaneous, rapid, and proceeds via transfer of AuCl4- to the oil phase, followed by homogeneous electron transfer generating uncontrolled polymer growth with larger (â¼50 nm) Au nanoparticles (NPs). Thus, miniaturization facilitates external, potential control and limits the reaction pathway. Atomic (AFM) and Kelvin probe force microscopies (KPFM) imaged the topography and work function distribution of the as-prepared films. The latter was linked to nanocluster distribution.
ABSTRACT
A monomer-through-pentamer series of oligo(1,8-pyrenylene)s was synthesized using a two-step iterative synthetic strategy. The trimer, tetramer, and pentamer are mixtures of atropisomers that interconvert slowly at room temperature (as shown by variable-temperature NMR analysis). They are liquids well below room temperature, as indicated by POM, DSC and SWAXS analysis. These oligomers are highly fluorescent both in the liquid state and in dilute solution (λF,max = 444-457 nm, φF = 0.80) and an investigation of their photophysical properties demonstrated that delocalization plays a larger role in their excited states than it does in related pyrene-based oligomers.
ABSTRACT
Two structural isomers of (9H-pyreno[4,5-d]imidazol-10-yl)-benzaldehyde, with para and meta substitution patterns, were synthesized by condensation of 4,5-pyrenedione with terephthalaldehyde and isophthalaldehyde, respectively. These new pyrenoimidazole derivatives were characterized by single-crystal X-ray crystallography, UV-vis absorption spectroscopy, fluorescence spectroscopy, and cyclic voltammetry to elucidate their structural, solid-state packing, and electronic properties. Interactions of these compounds with fluoride anions in polar organic solvents (acetone and dimethyl sulfoxide) were investigated by NMR, UV-vis, and fluorescence techniques in conjunction with density functional theory calculations. UV-vis analysis showed that the binding of the two pyrenoimidazolyl benzaldehydes with fluoride anions resulted in significant colorimetric responses, while fluorescence studies showed that the para-pyrenoimidazolyl benzaldehyde behaved as an intramolecular charge transfer fluorescent probe, exhibiting ratiometric sensing performance to efficiently detect and quantify fluoride anions at the sub-millimolar level.
ABSTRACT
Dithiafulvenyl (DTF) end groups were linked to the 1 and 8 positions of a pyrene core directly or via phenylene bridges to afford redox-active pyrene derivatives. Upon oxidation, the 1,8-bis(DTF)pyrene underwent stepwise electron transfers to form radical cation and dication species, whereas the phenylene-extended bis(DTF)pyrene derivative was cyclized into a macrocyclic trimer through sequential DTF oxidative coupling reactions in solution and in the solid state. The structural, electronic, and supramolecular properties of the pyrene-based macrocycle were investigated using various spectroscopic techniques and molecular modeling studies.
