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Recommendations are given concerning the terminology of concepts and methods used in spectroscopy in analytical chemistry, covering nuclear magnetic resonance spectroscopy, atomic spectroscopy, and vibrational spectroscopy. © 2021 IUPAC and De Gruyter. This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License. For more information, please visit: http://creativecommons.org/licenses/by-nc-nd/4.0/ 2021.

Raman scattering for a range of metal phthalocyanines using excitation frequencies from 457.9 to 1064 nm have been interpreted in the light of the recent DFT calculation on zinc phthalocyanine. The intention was to determine the features of the spectra that might be used for in situ analysis of specific phthalocyanines. B1 bands were found to be the most intense. The frequency of one band with a large C–N–C ring displacement is particularly sensitive to the metal ion size. The effect is determined not only by the size of the ion but also by the effect it has on ring shape. First and second order overtone bands of zinc and copper phthalocyanines are broadly similar, with some coupling differences at about 2000 cm−1. The region between 1350 and 1550 cm−1 has been little studied previously. It shows a remarkable sensitivity to the metal ion present and provides a specific signature for each phthalocyanine studied. In contrast, a study of α-, β-, γ- and e-copper phthalocyanines using 514.5 nm excitation showed very few differences, suggesting that intra- rather than intermolecular markers are most efficiently determined by Raman scattering. The study enables the interpretation of the Raman spectra of the phthalocyanines in terms of molecular structure and due to the resonant enhancement involved will enable the in situ identification of specific phthalocyanines in matrices.

The characterization of ink jet dyes and inks printed onto paper surfaces is of importance for the development of ink jet ink formulations and for use in forensic science. Raman spectroscopy is an effective and informative probe for this purpose if problems associated with fluorescence are overcome. A comparison is made here between two effective techniques, surface-enhanced resonance Raman scattering (SERRS) and near-infrared Fourier transform Raman scattering (NIR-FTR). SERRS provides a good method for obtaining in situ measurements using a visible laser system. It is fast (1–10 s accumulations) and requires very low laser powers (200 mW), and the spectral accumulation time is significantly longer. Both methods overcome fluorescence effectively in most samples studied; however, each is more effective than the other with selected inks and paper substrates. SERRS involves resonant enhancement of the chromophore of the dye in contact with the silver surface, and consequently it is the dye chromophore which is uniquely identified. With NIR-FTR, signals from the paper and the filler are also observed. Comparable spectral patterns with clear, explicable differences are obtained from each method, indicating in particular that SERRS spectra can be interpreted without recourse to specific surface selection rules. The combination of the two techniques provides some information on the electronic as well as the vibrational properties of the dyes in situ.

Density functional theory (DFT) calculations have been used to predict the IR and Raman spectra for zinc phthalocyanine (ZnPc). There is very good agreement in the frequency data (RMS error of 10 cm−1 for IR and 12 cm−1 for Raman scattering, with half of the bands in both cases predicted to within 6 cm−1). The precision of the data makes it possible to provide reliable frequency assignments and hence to interpret vibrational changes in terms of structural modifications. The sensitivity of the three IR bands between 700 and 800 cm−1 to the phthalocyanine polymorphic form is explained by the assignment of two modes to out-of-plane vibrations and one mode to an in-plane vibration. The out-of-plane vibrations are expected to be more sensitive to the solid-state packing. The most intense band in the Raman scattering, predicted at 1517 cm−1 for ZnPc, has large displacements on the C–N–C bridge bonds and shifts significantly with metal ion size, making it a good marker for changes in the metal ion environment.

The first use of Kerr gated fluorescence rejection Raman spectroscopy for the analysis of street samples of cocaine in a fluorescing matrix is reported.

The chapter illustrates specific applications of vibrational spectroscopy to colour analysis and colour probes. These include the effects of sample preparation variations for infrared spectroscopy on the colour properties and comparisons of differing laser techniques in Raman spectroscopy relative to the measurement required. A wide range of colour from prehistoric pigments to modern electronic dyes is considered. Several chemical groups, common in colour chemistry, are identified and comments made on the interpretation of the bands. Examples of reactions following tautomerism, hydration, and polymorphism are given. The use of Raman techniques, particularly surface enhanced resonance Raman spectroscopy (SERRS), as colour probes is highlighted and examples of the electronic uses of dyes are given. Brief mention is made of on/at line plant measurements and the spectroscopy of dyes in biological applications. Keywords: infrared; Raman; SERRS; colors; dyes; pigments; polymorphism; tautomerism; electronics

The assignment of the vibrational spectra of lithium hydroxide monohydrate, LiOH·H2O, has been controversial for more than half-a-century. Here we show that only the combination of all three forms of vibrational spectroscopy: infrared, Raman and inelastic neutron scattering spectroscopies coupled with periodic-density functional theory calculations is able to satisfactorily assign the spectra. All previous work based on empirical criteria is, at least partially, incorrect. The librational modes of water do not follow the expected rock > wag > twist order and the calculations indicate that complete or partial deuterium substitution would not be useful in assigning the modes.

Poly(aryl)amine based charge transfer materials (CTMs) are essential components in a range of present and future technologies, from the Xerox process to display devices based upon light emitting polymers (LEPs). However, there is a lack of detailed understanding regarding the electronic properties of CTMs in their various neutral and oxidized forms. This paper reports the use of an optically transparent thin layer electrochemical (OTTLE) cell in combination with a Raman microprobe system and DFT calculations to provide information on the molecular and electronic structure of the mono- and di-oxidized derivatives of the classic CTM N,N′-diphenyl-N,N′-bis(3-methylphenyl)(1,1′-biphenyl)-4,4′-diamine (TPD) and the closely related species N,N′-diphenyl-N,N′-bis(2,4-dimethylphenyl)(1,1′-biphenyl)-4,4′-diamine (DMTPD). The resonance Raman scattering profile easily discriminates between the monovalent and divalent cations while DFT calculations permit correlation of the observed vibrational frequencies with localized atomic displacements. The cations are best described in terms of a symmetrical (i.e. fully delocalized) structure. The high sensitivity of the method suggests that it should be appropriate for the observation of low concentrations of the various cations generated from TPD type CTMs during device operation.