Raman spectroscopy is an optical technique that can be used to evaluate the biomolecular composition of tissue and cell samples in a real-time and non-invasive manner. Subtle differences between datasets of spectra obtained from related cell groups can be identified using multivariate statistical algorithms. Such techniques are highly sensitive to small errors, however, and, therefore, the classification sensitivity of Raman spectroscopy can be significantly impacted by miscalibration of the optical system due to small misalignments of the optical elements and/or variation in ambient temperature. Wavenumber calibration is often achieved by recording the spectrum from a wavenumber reference standard, such as 4-acetamidophenol or benzene, which contains numerous sharp peaks in the fingerprint region. Here, we investigate a commercial polymer slide as a wavenumber reference standard for the calibration of Raman spectra. The Raman spectrum of this slide contains numerous sharp peaks in the fingerprint region. Unlike many other reference standards, the polymer slide is non-hazardous, has an indefinite lifetime, and is designed in the shape of a glass slide used for microscopy. We evaluate this reference in terms of accuracy and repeatability, and we compare with the established 4-Acetamidophenol wavenumber reference.
The synthesis of a series of PPV derivative polymers by the Wittig-Horner reaction is described. The structure of each polymer is varied and the effects of these variations on the optical properties is explored. The effects of alkyloxy side chains is observed between the PPV derivatives Poly(-p-phenylvinylene-co-2,5-bis-octyloxy phenylvinylene.) PPV-OPV and Poly (para-2,5-bis-(n-octyloxy)-phenylvinylene) POPV. The phenyl units of the soluble PPV derivative POPV are replaced by alternate naphthyl units in the polymer Poly(2,5-bis(n-octyloxy)-1,4-phenylene vinylene-1,5-bis(n-octyloxy)-2,6-naphthylene vinylene) POPN-ONV and then fully by naphthyl units in Poly(2,6-bis-(n-octyloxy)-1,5-NaphthyleneVinylene) PONV. The addition of alkyloxy sidechains served to red shift the fluorescence emission as expected. The systematic conversion of phenyl to naphthyl units blue shifted the emission considerably while reducing the Stokes shift. There is evidence to suggest some localization of the pi electrons over the aromatic units of the polymer backbone. PONV is shown to have greater stability towards photo-oxidation then either POPV or PPV-OPV.
A series of π conjugated systems were studied by absorption, photoluminescence and vibrational spectroscopy. As is common for these systems, a linear relationship between the positioning of the absorption and photoluminescence maxima plotted against inverse conjugation length is observed. The relationships are in good agreement with the simple particle in a box method, one of the earliest descriptions of the properties of one-dimensional organic molecules. In addition to the electronic transition energies, it was observed that the Stokes shift also exhibited a well-defined relationship with increasing conjugation length, implying a correlation between the electron-vibrational coupling and chain length. This correlation is further examined using Raman spectroscopy, whereby the integrated Raman scattering is seen to behave superlinearly with chain length. There is a clear indication that the vibrational activity and thus nonradiative decay processes are controllable through molecular structure. The correlations between the Stokes energies and the vibrational structure are also observed in a selection of PPV based polymers and a clear trend of increasing luminescence efficiency with decreasing vibrational activity and Stokes shift is observable. The implications of such structure property relationships in terms of materials design are discussed.
Single wall carbon nanotubes are insoluble in most organic solvents such as toluene. Improvements in the solubility of the single wall carbon nanotubes are however seen as a result of specific interactions with molecules such as terphenyl and anthracene. Suspensions formed in toluene with these molecules and the single wall carbon nanotubes are seen to be stable over prolonged periods. Spectroscopic analysis clearly shows an interaction between the carbon nanotubes and the molecules. It is proposed in this study that the use of these more simple molecular systems may help elucidate the nature and extent of the interaction in more complex composite based systems.