Side-chain influence on the mass density and refractive index of polyfluorenes and star-shaped oligofluorene truxenes

This work is part of the TIRAMISU project, funded by the European Commission’s Seventh Framework Programme (FP7/2007-2013) under grant agreement n◦284747 and the Engineering and Physical Sciences Research Council (EPSRC) grants EP/J009016/1 and EP/F059922/1. I.D.W.S. and P.J.S. are Royal Society Wolfson Research Merit Award holders.The density of organic semiconductor films is an important quantity because it is related to intermolecular spacing which in turn determines the electronic and photophysical properties. We report thin film density and refractive index measurements of polyfluorenes and star-shaped oligofluorene truxene molecules. An ellipsometer and a procedure using a spectrophotometer were used to determine film thickness and mass of spin-coated films, respectively. We present a study of the effect of alkyl side-chain length on the volumetric mass density and refractive index of the materials studied. The density measured for poly(9,9-di-n-octylfluorene) (PF8) was 0.88 ± 0.04 g/cm3 and decreased with longer alkyl side chains. For the truxene molecule with butyl side chains (T3 butyl), we measured a density of 0.90 ± 0.04 g/cm3, which also decreased with increasing side-chain length.PostprintPeer reviewe

DNA binding and oxidative DNA cleavage activity of (μ-oxo)diiron(III) complexes in visible light

Four (μ-oxo)diiron(III) complexes [Fe2(μ-O)(H2O)2B4](ClO4)4 ( 1 and 2) and [Fe2(μ-O)(μ-O2CMe)B4](ClO4)3 ( 3 and 4), where B = 1,10-phenanthroline (phen) and dipyrido[3,2-d:2',3'-f]quinoxaline (dpq), are prepared and their DNA binding and cleavage activity studied. The complexes show DNA binding propensity giving Kb values of 3.6-9.3 × 104 M-1. The viscosity and DNA melting data suggest a surface and/or groove binding nature of the complexes to calf thymus (CT) DNA. The DNA binding data obtained from isothermal calorimetric study indicate two binding modes involving surface aggregation and/or partial intercalation of the phenanthroline bases to CT DNA. All the complexes show chemical nuclease activity in the presence of 3-mercaptopropionic acid as a reducing agent following a mechanistic pathway that involves formation of superoxide and hydroxyl radicals. Photoirradiation of pUC19 DNA at 365 nm in the presence of 1-4 show that the complexes, barring 1, are efficient photocleavers of supercoiled DNA to its nicked circular form. Complexes 2-4 display photocleavage activity in visible light of different wavelengths. Complexes 3 and 4 exhibit significant DNA cleavage activity in red light of 633 nm, the wavelength known for the activity of the photodynamic therapeutic drug Photofrin®. The mechanistic study using various additives suggests a minor groove binding nature of the complexes with the formation of singlet oxygen from the quinoxaline moiety of dpq and hydroxyl radical from photodecarboxylation of the acetate ligand as the reactive oxygen species

Photo-induced double-strand DNA and site-specific protein cleavage activity of L-histidine (mu-oxo)diiron(III) complexes of heterocyclic bases

Three oxo-bridged diiron(III) complexes of L-histidine and heterocyclic bases [Fe-2(mu-O)(L-his)(2)(B)(2)](ClO4)(2) (1-3), where B is 2,2'-bipyridine (bpy),1,10-phenanthroline (phen), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq), were prepared and characterized. The bpy complex 1 was structurally characterized by X-ray crystallography. The molecular structure showed a {Fe-2(mu-O)} core in which iron(III) in a FeN4O2 coordination is bound to tridentate monoanionic L-histidine and bidentate bpy ligands. The Fe center dot center dot center dot Fe distance is similar to 3.5 angstrom. The Fe-O-Fe unit is essentially linear, giving a bond angle of similar to 172 degrees. The complexes showed irreversible cyclic voltammetric cathodic response near -0.1 V vs. SCE in H2O-0.1 M KCl. The binuclear units displayed antiferromagnetic interaction between two high-spin (S = 5/2) iron(III) centers giving a -J value of -110 cm(-1). The complexes showed good DNA binding propensity giving a binding constant value of similar to 10(5) M-1. Isothermal titration calorimetric data indicated single binding mode to the DNA. The binding was found to be driven by negative free energy change and enthalpy. The dpq complex 3 showed oxidative double-strand DNA cleavage on exposure to UV-A and visible light. The phen complex 2 displayed single-strand photocleavage of DNA. The DNA double-strand breaks were rationalized from theoretical molecular docking calculations. Mechanistic investigations showed formation of hydroxyl radicals as the reactive species through photodecarboxylation of the L-histidine ligand. The complexes exhibited good binding propensity to bovine serum albumin (BSA) protein in Tris-HCl/NaCl buffer medium. The dpq complex 3 showed UV-A light-induced site-specific oxidative BSA cleavage forming fragments of similar to 45 kDa and similar to 20 kDa molecular weights via SOH pathway

Photo-induced double-strand DNA and site-specific protein cleavage activity of L-histidine (μ-oxo)diiron(III) complexes of heterocyclic bases

Three oxo-bridged diiron(III) complexes of L-histidine and heterocyclic bases [Fe2(μ-O)(L-his)2(B)2](ClO4)2 (1-3), where B is 2,2'-bipyridine (bpy), 1,10-phenanthroline (phen), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq), were prepared and characterized. The bpy complex 1 was structurally characterized by X- ray crystallography. The molecular structure showed a {Fe2(μ-O)} core in which iron(III) in a FeN4O2 coordination is bound to tridentate monoanionic L-histidine and bidentate bpy ligands. The Fe···Fe distance is ~3.5 Å. The Fe-O-Fe unit is essentially linear, giving a bond angle of ~172°. The complexes showed irreversible cyclic voltammetric cathodic response near −0.1 V vs. SCE in H2O-0.1 M KCl. The binuclear units displayed antiferromagnetic interaction between two high-spin (S=5/2) iron(III) centers giving a −J value of ~110 cm−1. The complexes showed good DNA binding propensity giving a binding constant value of ~105 M−1. Isothermal titration calorimetric data indicated single binding mode to the DNA. The binding was found to be driven by negative free energy change and enthalpy. The dpq complex 3 showed oxidative double-strand DNA cleavage on exposure to UV-A and visible light. The phen complex 2 displayed single-strand photocleavage of DNA. The DNA double-strand breaks were rationalized from theoretical molecular docking calculations. Mechanistic investigations showed formation of hydroxyl radicals as the reactive species through photodecarboxylation of the L-histidine ligand. The complexes exhibited good binding propensity to bovine serum albumin (BSA) protein in Tris-HCl/NaCl buffer medium. The dpq complex 3 showed UV-A light-induced site-specific oxidative BSA cleavage forming fragments of ~45 kDa and ~20 kDa molecular weights via OH pathway

Side-chain influence on the mass density and refractive index of polyfluorenes and star-shaped oligofluorene truxenes

The density of organic semiconductor films is an important quantity because it is related to intermolecular spacing which in turn determines the electronic and photophysical properties. We report thin film density and refractive index measurements of polyfluorenes and star-shaped oligofluorene truxene molecules. An ellipsometer and a procedure using a spectrophotometer were used to determine film thickness and mass of spin-coated films, respectively. We present a study of the effect of alkyl side-chain length on the volumetric mass density and refractive index of the materials studied. The density measured for poly(9,9-di-n-octylfluorene) (PF8) was 0.88 ± 0.04 g/cm3 and decreased with longer alkyl side chains. For the truxene molecule with butyl side chains (T3 butyl), we measured a density of 0.90 ± 0.04 g/cm3, which also decreased with increasing side-chain length