Analysis of redox-active polymers by MALDI-TOF mass spectrometry: Poly(3-hexylthiophene) and functionalized dendrimers

The electron-transfer matrices for matrix-assisted desorption/ionization (MALDI)-mass spectrometry of small non-polar, redox-active analytes are evaluated. Results show that terthiophene can be used successfully as a matrix for the mass spectral characterization of the electronically conducting polymer poly(3-hexylthiophene). The molecular weight values obtained by MALDI-MS are significantly lower than those provided by gel permeation chromatography. In the analysis of redox-active dendrimer, anthracene and terthiophene are the gentlest MALDI matrices, causing much less fragmentation than dithranol or 2,5-dihydroxybenzoic acid

On-line capillary electrophoresis-electrospray ionization mass spectrometry using a polymerized anionic surfactant

On-line capillary electrophoresis - electrospray ionization - mass spectrometry (CE-ESI-MS) has been used to determine the tricyclic antidepressant drugs (imipramine, doxepin, and amitriptyline) as well as the β-adrenergic blocker drugs (propranolol and alprenolol). A CE-ESI-MS interface linking a manually operated CE system and a Finnigan MAT-900 sector mass spectrometer (with an Analytica electrospray ionization source) has been constructed in-house and employed for this study. Although a water/methanol based capillary zone electrophoresis (CZE) buffer was initially used to determine these analytes, enhanced resolution was obtained by addition of a polymerized surfactant, i.e., poly-sodium undecylenic sulfate (poly-SUS), into the electrokinetic chromatography (EKC) buffer. When a low concentration of this poly-SUS surfactant was added to a volatile EKC buffer, these structurally similar cationic drugs were EKC separated and on-line detected by ESI-MS

Remarkable Photophysics and Amplified Quenching of Conjugated Polyelectrolyte Oligomers

We report the photophysics and fluorescence quenching of a series of monodisperse, anionic π-conjugated oligomers that are molecularly dissolved in aqueous solution. These structurally well-defined oligomers feature oligo(phenylene ethynylene) backbones with two -CH2COO(-) units on each repeat unit, with overall lengths of 5, 7, and 9 repeats. The ionic oligomers display a structured fluorescence band with high quantum efficiency in water, in contrast to the low fluorescence quantum efficiency and pronounced aggregation displayed by structurally similar oligomeric and polymeric (phenylene ethynylene) conjugated polyelectrolytes studied previously. Stern-Volmer (SV) fluorescence quenching studies using cationic charge- and energy-transfer quenchers reveal that all of the oligomers give rise to SV quenching constants (KSV) in excess of 10(6) M(-1), with values increasing with oligomer length, consistent with the amplified quenching effect. The amplified quenching effect is proposed to occur due to the formation of comparatively small oligomer aggregates

Phase transition pattern of 2,5-diphenyloxazole/γ-cyclodextrin (PPO/γ-CD) self-assembly aggregates

The molecule 2,5-diphenyloxazole (PPO) organizes into non-covalently bonded self-assembled aggregates of guest-host complexes with γ-cyclodextrin (γ-CD) in aqueous solutions. This structure is held together by weak interactions between the PPO and the γ-CD molecules. Therefore a small activation energy allows deterioration of these self-assembled aggregates. In this study, we report the effect of temperature and pH on this unique ensemble of aggregates. We report a phase transition pattern in which the structure disassembles from long to short (i.e. basic unit) aggregates. The relative fluorescence intensities of the excimer and monomer of PPO have been used to study this transition. Earlier investigations reported that these self-assembled aggregates were destroyed by an increase in temperature up to 80°C. In this study, we examined the effect of temperature on this structure and found a phase transition pattern of the temperature-dependent structure. Both the intensity and polarization of the steady state fluorescence reveal similar values of the critical temperature at 46±8°C and 49±7°C for the monomer and excimer fluorescence respectively. In addition, earlier studies proposed that hydrogen bonding between the guest and host molecules may play an active role in stabilizing the linear beads. We examined this hypothesis by changing the pH to an acidic or basic medium. A change in the aggregates was observed at approximately pH 12, which is the pKa value of γ-CD. For the pH range 10-13, a phase transition is centered at about pH 12. © 1995

Spray coatable electrochromic dioxythiophene polymers with high coloration efficiencies

Four new disubstituted propylenedioxythiophene polymers have been synthesized by Grignard metathesis on the 1-5 g scale. All polymers were found to be soluble in chloroform, methylene chloride, toluene, and tetrahydrofuran and were fully structurally characterized having GPC determined number-average molecular weights ranging from 33000 to 47000 g mol(-1). Dilute polymer solutions in toluene exhibited strong red fluorescence with moderate quantum efficiencies from 0.38 to 0.50. Homogeneous thin films were formed by electropolymerization and spray casting polymer solutions onto ITO coated glass slides at thicknesses of ca. 150 nm. The films were electroactive, switching from a dark blue-purple to a transmissive sky blue upon p-doping, often with subsecond switching times, and high electrochromic contrast luminance changes (% DeltaY) of 40-70%. These studies revealed that the branched derivatives, [poly(3,3-bis(2-ethylhexyl)-3,4-dihydro-2H-thieno[3,4-b] [1,4] dioxepine)] and [poly(6,8-dibromo-3,3-bis(2-ethylhexyloxymethyl)-3,4-dihydro-2H-thieno[3,4-b] [1,4]dioxepine)], gave an electrochemical response and associated color change over a much smaller voltage range in comparison to the linear chain substituted derivatives, [poly(3,3-dihexyl-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine)] and [poly(3,3-bis(octadecyloxymethyl)-3,4-dihydro-2H-thieno[3,4-b] [1,4]dioxepine)]. Composite coloration efficiency values were found up to 1365 cm(2)/C; this was considerably larger than values obtained from previously studied alkylenedioxythiophene based polymers (similar to375 cm(2)/C)

Remarkable Photophysics and Amplified Quenching of Conjugated Polyelectrolyte Oligomers

We report the photophysics and fluorescence quenching of a series of monodisperse, anionic π-conjugated oligomers that are molecularly dissolved in aqueous solution. These structurally well-defined oligomers feature oligo­(phenylene ethynylene) backbones with two −CH₂COO^– units on each repeat unit, with overall lengths of 5, 7, and 9 repeats. The ionic oligomers display a structured fluorescence band with high quantum efficiency in water, in contrast to the low fluorescence quantum efficiency and pronounced aggregation displayed by structurally similar oligomeric and polymeric (phenylene ethynylene) conjugated polyelectrolytes studied previously. Stern–Volmer (SV) fluorescence quenching studies using cationic charge- and energy-transfer quenchers reveal that all of the oligomers give rise to SV quenching constants (<i>K</i>_SV) in excess of 10⁶ M^–1, with values increasing with oligomer length, consistent with the amplified quenching effect. The amplified quenching effect is proposed to occur due to the formation of comparatively small oligomer aggregates