Solution State Absorption Research Articles

Structural and spectroscopic insights on the coordination chemistry of the rigid heterotopic chelating ligand 1H-pyrazolo[4,3-h]quinoline

In this work, we report the coordination chemistry of a rigid heterotopic ligand 1H-pyrazolo[4,3-h]quinoline HL1 in copper(II) and zinc(II) complexes and examine both the structural properties and solution-phase behavior of these species. On reaction with zinc(II) nitrate in acetonitrile, a mononuclear complex [Zn(HL1)2(OH2)2](NO3)2 1 is generated, where a size mismatch between the metal ion and the binding pocket leads to an anomalously long Zn–N bond to the pyrazole nitrogen. This is consistent with solution-state absorption and fluorescence measurements which indicate a relatively low stability constant logβ of 9.1(3) in acetonitrile. The reaction of HL1 with copper(II) nitrate in methanol gave four new crystalline phases, the major forms of which are two polymorphs of [Cu2(μ2-L1)2(NO3)2(MeOH)2] 2α and 2β which also constitutes the dominant solution-phase behavior of this mixture. Additionally, trace amounts of the nitric acid salt of HL1 were crystallized along with the slow formation of a tetranuclear species [Cu4(μ2-L1)6(OH2)2](NO3)2 · 2MeOH 3 which also features anomalously long bridging distances from L1 as a result of its backbone rigidity.

Boron subphthalocyanine polymers: Avoiding the small molecule side product and exploring their use in organic light‐emitting diodes

ABSTRACTIn this study, we set out the steps to efficiently synthesize boron subphthalocyanine (BsubPc)‐containing polymers while circumventing the formation of a known side product. The synthesis was achieved using the post‐polymerization coupling reaction of a carboxylic acid functional prepolymer with bromo‐BsubPc. We have earlier shown that when copolymerizing styrene and acrylic acid (AA) a significant amount of an undesired side product is formed. In this study, we have determined that this side product persisted when styrene was copolymerized with AA or n‐butyl acrylate but could be avoided when styrene was copolymerized with methacrylic acid (MAA), methyl methacrylate, or acrylonitrile. Therefore, MAA/styrene copolymer, synthesized by nitroxide‐mediated polymerization was chosen to be coupled to BsubPc. The resulting BsubPc polymer was found to have similar electrochemical properties, solution state absorption and photoluminescence characteristics when compared against a small molecule model compound although the solid‐state PL emission of the polymer was found to be excitation wavelength dependent. Finally, preliminary organic light‐emitting diodes (OLEDs) were fabricated to assess the potential role(s) of the BsubPc polymer in organic electronic devices. These OLEDs represent the first‐solution processed organic electronic devices containing BsubPc polymers as a functional material. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 1996–2006

Investigating the effect of conjugation in MEH-PPV

Solution state absorption and fluorescence of samples of fully and partially conjugated MEH-PPV at 77K and 300K have been measured to probe the distribution of conjugated segments within the polymer. The absorption of the partially conjugated polymer is at shorter wavelength and has a larger full width at half maximum at all temperatures than that of the fully conjugated polymer. The spectra are analysed by considering the polymer chain to be made up of a number of non interacting conjugated segments. Using this approach it is possible to explain all the features seen in the spectra.

Structures of the Copper(I) and Copper(II) Complexes of 2,9-Diphenyl-1,10-phenanthroline: Implications for Excited-State Structural Distortion.

The syntheses, crystal structures, and electronic absorption spectra of the copper(I) and copper(II) complexes of 2,9-diphenyl-1,10-phenanthroline (dpp) are reported. The complex [Cu(dpp)(2)](PF(6)) (1) crystallizes in space group P2(1)/c with a = 11.081(4) Å, b = 25.491(8) Å, c = 14.263(5) Å, beta = 92.84(3) degrees, Z = 4, and V = 4024(2) Å(3). For 4813 unique data with F > 4.0sigma(F), R = 5.41% and R(w) = 6.43%. The coordination geometry about the copper(I) center in [Cu(dpp)(2)](+) is best described as distorted tetrahedral with approximate C(2) symmetry. The structure of [Cu(dpp)(2)](+) is largely determined by interligand pi-stacking interactions that occur between the phenyl groups of one ligand and the phenanthroline moiety of the other ligand. Solution-state absorption and (1)H NMR spectra indicate that the [Cu(dpp)(2)](+) complex is fluxional in solution, rocking between two enantiomeric structures of C(2) molecular symmetry through an intermediate of C(s)() symmetry. The complex [Cu(dpp)(2)](ClO(4))(2) (2) crystallizes in space group P&onemacr; with a = 7.809(3) Å, b = 13.027(6) Å, c = 20.344(10) Å, alpha = 87.68(4) degrees, beta = 89.16(4) degrees, gamma = 79.26(4) degrees, Z = 2, and V = 2032(1) Å(3). For 4943 unique data with F > 4.0sigma(F), R = 5.22% and R(w) = 5.37%. The coordination geometry about the copper(II) center in [Cu(dpp)(2)](2+) is best described as flattened tetrahedral with approximate D(2) symmetry. There are no interligand pi-stacking interactions in the structure of [Cu(dpp)(2)](2+). The four-coordinate geometry in [Cu(dpp)(2)](2+) persists in solution on the basis of solution-state and solid-state absorption spectroscopy. Structural distortion in the metal-to-ligand charge-transfer excited state of [Cu(dpp)(2)](+) is discussed on the basis of the structures of 1 and 2.