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In this work a study is reported on the Raman and UV–vis absorption spectra of recently synthesized poly (3-hexylthiophene-2,5-diyl) (P3HT) samples whose degree of head-to-tail (H-T) regioregularity has been, on purpose, modified in the range 98%-64% by a controlled insertion of head-to-head (H-H) coupled bithiophene monomers. The materials under study show the strongest Raman scattering line near 1450 cm−1, when recorded in off-resonance conditions. Based on the Effective Conjugation Coordinate theory we learn that this scattering originates from the collective CC stretching mode along the polymer backbone (Я mode). A curve fitting analysis reveals that this line is the result of the convolution of three strong components at 1445 cm−1, 1450 cm−1 and near 1480 cm−1 with different relative intensities as function of the sample regioregularity. These lines are assigned to polymer chains which take up different conformations namely: i) co-planar sequences of thiophene units, labelled as hairy-A, which originate the crystalline domains of form-1, ii) conformationally slightly distorted sequences of thiophene units, labelled as hairy-B, and iii) highly distorted/disordered sequences of thiophene units which originate the amorphous phase. Also the UV–vis absorption spectra recorded on thin films of the same materials can be interpreted as the convolution of the absorptions originated from the polymers chains in the three different conformations as in i), ii), and iii). With multi-wavelength resonance Raman spectroscopy is thus possible to enhance selectively the scattering of each type of chain. From the Raman data recorded in off-resonance a straightforward method to obtain the relative amount of the above structures is proposed, showing that solid rr-P3HT at room temperature is composed approximately by 50% of hairy-A chains and 50% of hairy-B chains with a negligible contribution by the amorphous phase. The information derived from this study are of great help for the understanding of the conformational structure in the solid state of the technologically relevant parent molecule rr-3PHT.

Air pollution mostly originating from car exhaust and industrial emissions is seriously endangering human health. The study of toxic effects of particulate matter (PM) is a subject of very active research that covers a broad field from biology to chemistry and technology. The main issue of these works is the understanding of the oxidative properties of PM. In this paper, we present a quantitative analytical method based on the resonance Raman spectroscopy of cytocrome c that can be used to monitor the oxidative reactions that may take place between biological samples and PM. Copyright © 2016 John Wiley & Sons, Ltd.

Carbonaceous particles of environmental origin are practically insoluble, which constitutes an obstacle to many chemical physical characterization techniques. Micro-Raman spectroscopy overcomes the sample preparation step and can be applied on the as-received sample and even in situ, with nowadays commercially available portable Raman equipment. Multivariate statistical analysis of Raman data recorded on a variety of carbonaceous particles of different origin, through a molecular interpretation of the signal, shows that the use of Raman spectroscopy with several excitation sources can provide a useful tool for assisting the characterization of various forms of environmental carbon matter. Copyright © 2015 John Wiley & Sons, Ltd.

New data on vibrational properties of calcium oxalates and their controversial transformation mechanism are presented. We have focused on whewellite (CaC2O4·H2O) and weddellite [CaC2O4·(2 + x) H2O], the most common phases of calcium oxalate; these compounds occur in many organisms, in kidney stones and in particular kinds of films found on the surface of many works of art. Low temperature experiments carried out by Fourier transform infrared spectroscopy have highlighted both the high structural order in the crystalline state of whewellite and the disordered distribution of the zeolitic water molecules in weddellite. The synthesised nanocrystals of weddellite have been kept under different hygrometric conditions in order to study, by X-ray powder diffraction, the role of "external" water molecules on their stability. Moreover, in order to identify the different kinds of water molecules, a re-investigation, supported by quantum chemical calculations, of the observed vibrational spectra (IR and Raman) of whewellite has been conducted. © 2014 Published by Elsevier B.V.

We review the theory for overtones and combinations in resonant Raman spectroscopy introduced by Nafie, Stein and Peticolas in 1971 on the basis of time-ordered diagrams, and we apply it to β-carotene with the support of density functional theory calculations. Comparison with experimental results obtained by Tasumi's group in 1994 is provided. The theory here presented allows a prompt evaluation of resonant Raman intensities with presently available quantum chemistry tools. Copyright © 2014 John Wiley & Sons, Ltd.

This study aims to evaluate the relevance of portable Raman and portable mid-Fourier transform infrared (FTIR) reflectance instruments in monitoring the synthetic treatments applied on plaster substrates, a crucial issue in a conservation work. Some polymeric consolidants and protectives have a relatively short life owing to their degradation, and after some years the surface should be retreated. It follows that any information about the presence and composition of the products applied, their chemical transformations and their distribution on the surfaces is essential. For these purposes, conservation scientists should seek and test new in situ methods, and this is of utmost importance especially in the case of buildings, considering their large dimensions and consequent extensive mapping. The effectiveness of portable Raman and portable mid-FTIR reflectance instruments has been compared by analysing a set of laboratory specimens prepared and treated with variable amounts of products belonging to three classes of polymers; the spectroscopic investigation highlighted, for the first time, the limits and the advantages of portable Raman and portable mid-FTIR reflectance instruments in the detection of small amounts of products commonly employed for the conservation of plasters.

The chemical nature of the red pigment of Corallium rubrum (CR) has not yet been clearly identified. We have recorded the Raman spectra of CR, canthaxantin, and parrot feather, and we propose an interpretation with the help of quantum chemistry and of the effective conjugation coordinate theory, which accounts for the main Raman lines (ν1, ν2, ν3) as originating from the polyene backbone. In this study, two additional lines in the 1000 cm−1 range (ν4 and ν5) are considered as well as a series of overtones and combinations in the second order Raman spectrum (2000–3000 cm−1). Density Functional Theory calculations predict that, moving with successive methylation from a simple unsubstituted polyene chain with 9 C═C bonds (as psyttacofulvins) to a 9, 9′, 13, 13′ tetramethylated chain (as carotenoids), the geometric structures of the molecules and their Raman spectra show changes that can be rationalized if the effective conjugation coordinate theory is extended to account for mechanical confinement. This turns out to be a new concept that helps the interpretation of the Raman spectra of partially methylated conjugated oligoenes. Evidence is found that the main component of the pigment of CR does not posess a fully demethylated polyene chain (psyttacofulfine) nor a tetramethylated chain (carotenoid), thus indicating that the polyene chain is partially methylated. Because we consider resonance Raman spectra, the target of this study is the structure of the polyene backbone; no direct spectroscopic information can be obtained in this way on the chemical nature of the groups attached to both chain ends. Copyright © 2012 John Wiley & Sons, Ltd.

Linear sp-carbon polyynes are ideal molecules for the direct investigation of the physical properties of one-dimensional conjugated systems. Traditionally, the main obstacle to the study of these systems has been their instability under normal laboratory conditions. Thanks to improved chemical syntheses, a broadened range of polyynes is now available for study, including the hydrocarbon series endcapped with adamantyl groups, Ad[n]. In this work, the quantitative Raman spectroscopic analysis is reported for each member of this homologous series. The Raman scattering intensities corresponding to the major features of the polyyne segment (i.e., the effective conjugation coordinate or Я lines) are then used to evaluate the nonlinear optical (NLO) behavior via determination of the vibrational contribution to the second hyperpolarizability (γvib). This study shows that γvib values as a function of length are of the same order of magnitude as those arising from the electronic contribution to the molecular second hyperpolarizability, γele, as reported for triisopropylsilyl polyynes, TIPS[n], using the differential optical Kerr effect technique. The nonlinear response for Ad[n] polyynes, supported by the analogous response for TIPS[n] polyynes, confirms that linear sp-carbon molecules have large second hyperpolarizabilities that show a power-law increase in γ-values versus length that is larger than other known π-conjugated systems, such as polyenes. Furthermore, the NLO response of polyynes versus length approaches the theoretical limit described by Kuzyk more closely than other conjugated organic oligomers. Copyright © 2012 John Wiley & Sons, Ltd.

Infrared (IR) and Raman spectroscopy have been used to examine the vibrational characteristics of a series of three macrocyclic tetraynes in comparison with an acyclic analog. By changing the length of the alkyl tether of the macrocycles, varying degrees of bending of the tetrayne moiety can be achieved, and the joint use of IR and Raman spectroscopies provides an avenue to probe the impact of bending on the sp-chain. The spectroscopic data show a general trend toward decreasing activation of Raman bands in the IR spectra, and vice versa, as bending of the polyyne chain is decreased. Density functional theory calculations provide a detailed rationalization of the experimental observations. Copyright © 2011 John Wiley & Sons, Ltd.

A first-principles assisted study of the Raman spectrum associated with the photoactive chromophore in bacteriorhodopsin (bR) allowed the elucidation of the effective coupling existing between the π electrons of the retinylidene chromophore and the local environment of the Schiff base. The role of the counter-ion on the electronic and vibrational structure of the chromophore is investigated by means of density functional theory (DFT) calculations. Several molecular models of the retinylidene chromophore interacting with different counter-ions facing the Schiff base have been considered. The counter-ion induces a strong modulation of the position of both the UV–vis absorption maximum and the strong Raman active collective CC stretching mode, related to the effective conjugation coordinate (ECC). Experimental Raman and UV–vis absorption data are interpreted in the light of these theoretical findings. The data collected in this paper provide an interesting accumulation of points along the optical gap versus ECC wavenumber relationship. Copyright © 2011 John Wiley & Sons, Ltd.

Molecules composed of sp-hybridized carbon chains (polyynes) are the simplest of the known conjugated organic oligomers. In comparison to their counterparts such as polyacetylene and polydiacetylene, however, the formation of polyynes has traditionally posed a difficult synthetic challenge. In particular, there is no reliable method to form end-capped polyethynylene, and monodisperse polyynes have therefore been assembled. As a result, structure–property relationships for shorter polyynes have been relatively well established in recent years, while extension of these trends toward longer polyynes has remained a difficult task. Using the Fritsch–Buttenberg–Wiechell (FBW) rearrangement, the formation of diynes through decaynes has become possible and has provided a unique chance to explore the physical characteristics of conjugated polyyne chains. This paper highlights recent advances in the synthesis of extended polyynes, as well as interesting aspects of their NMR, Raman, and UV/vis spectroscopic analyses. These synthetic achievements offer the opportunity to predict some of the properties of the carbon allotrope carbyne. In particular, a set of X-ray crystallographic analyses of t-Bu end-capped polyynes (tBu[n]) shows a definitive experimental trend in reduced bond-length alternation (BLA).

A theoretical model based on Huckel theory is presented and applied to the infinite linear carbon chain. The effect of Peierls distortion, π-electron confinement and electron–phonon coupling are interpreted on the basis of measurable parameters such as bond length alternation, electronic gap and Raman wavenumbers. A diagram is presented where the correlation among these quantities is shown on the basis of the model adopted. The effect of π-electron confinement on experimental data can be directly evaluated, and insights on the physical properties of these materials can be derived. Copyright © 2009 John Wiley & Sons, Ltd.

Apomorphine (aporphine-10,11-diol, CA Registry Number 58004) is a non-narcotic derivative of morphine discovered in 1869 by Mattheisen1 and it is a well-known potent short-acting dopamine agonist at D1 and D2 dopamine receptors, typically used in the treatment of patients with advanced Parkinson's disease (PD). To identify the unknown vibrational spectrum of this compound, apomorphine bare salt and its commercial drug formulation (Apofin) were examined by means of Raman spectroscopy. In the Raman spectrum of apomorphine (both bare salt and commercial drug), two strong characteristic signals were found, which were assigned with the help of first-principles calculations: the band at 1589 cm−1 (assigned to the stretching mode of the B aromatic ring coupled with CH in-plane bending) and the band at 1302 cm−1 (assigned to O-H in-plane bending and CH2 twisting and wagging vibrations). Copyright © 2009 John Wiley & Sons, Ltd.

Amorphous fluorinated optical polymers, characterized by high transparency in the visible and near infrared spectra, high glass transition temperature and very good resistance to chemical environment, have been developed by co-polymerisation of tetrafluoroethylene (TFE) and 2,2,4-trifluoro-5-trifluoromethoxy-1,3-dioxole (TTD). In this work we study at molecular level the effect of the introduction of the bulky TTD unit in a perfluoroalkyl chain. In particular the effect on the molecular structure and chain flexibility is investigated and spectroscopic markers correlated to chemical and structural defects are identified. The study includes a thorough experimental spectroscopic analysis (infrared and Raman spectra) of several different copolymer samples and a modelling based on Density Functional Theory calculations and semiempirical calculations on suitable model molecules.

The modulation of the longitudinal optical (LO) phonon branch of a linear, infinite carbon chain (carbyne) by the degree of bond length alternation (BLA) is discussed in relation to the wavenumber dispersion of the strongest Raman line of oligoynes. Furthermore, the potential energy surface describing the Peierls distortion of the infinite 1D crystal has been determined theoretically through DFT calculations with periodic boundary conditions. A two-minima potential surface has been obtained as a function of BLA parameter, under the constraint that the diatomic unit cell keeps its translational period fixed to the optimized value. In this way, it has been possible to obtain the generalized harmonic force constant associated with the LO phonon at the Γ point. The results obtained can be related to the observed behavior of the LO Raman line upon the temperature-driven phase transition towards a cumulenic structure. Copyright © 2007 John Wiley & Sons, Ltd.

A novel SERS (surface-enhanced Raman scattering) sensor has been recently developed; its peculiar geometry is able to increase considerably both the SERS active surface and the number of internal reflections at the interface between silica and silver, thus allowing an increase of the signal intensity. The aim of this work is to demonstrate that this sensor could be efficiently used to detect some molecules such as illegally used veterinary medicine (crystal violet and malachite green) below the ppb detection limit. The advantages of this sensor with respect to other detection techniques are not only the higher sensitivity, but also the fast response and the possibility of coupling with a portable Raman spectrometer for “on-field” measurements. The ability of the sensor to work under real environmental conditions in the presence of many cationic and anionic species has been tested both in solutions containing sodium and chlorine ions and in water coming from the aqueduct of Milan and from the (normally polluted) river Serio.

The FT-Raman spectra of a series of mechanically prepared MgCl 2 –TiCl 4 samples with increasing content of TiCl 4 have been recorded. Raman scattering lines in the range 600–100 cm −1 reveal the formation of TiCl 4 molecules complexed on the lateral cuts of activated MgCl 2 crystals. This pattern of lines suggests that atleast three types of complexes are formed during the grinding process and their relative concentration depend on the starting concentration of TiCl 4 . Two types of these complexes have been shown to be unstable and easily removed when the samples are washed with n -hexane. In the former two cases TiCl 4 molecules are seemingly physisorbed and/or weakly complexed on MgCl 2 . The remaining complex is stable and it is found in every sample also after washing. This stable complex shows Raman lines which can be interpreted as originated from the complexed TiCl 4 molecules with the Ti atoms in an octahedral coordination. On the other hands also monomeric TiCl 4 species complexed along the (1 1 0) lateral cut or dimeric TiCl 4 species complexed along the (1 0 0) lateral cuts of the MgCl 2 crystal can take up a geometry with the Ti in an octahedral coordination. Both these structures have been considered in this work. Calculated Raman spectra, molecular energy considerations and Raman lines intensity ratios strongly support the fact that the stable complexes are the monomeric TiCl 4 species complexed along the (1 1 0) MgCl 2 lateral cuts. A spectroscopic quantitative determination of the complexed TiCl 4 for this class of material is proposed.

Photochromic diarylethene molecules are characterized by electronic properties significantly different in the two isomers. In this work, we are particularly concerned with the vibrational contribution to second order hyperpolarizabilities. We show that a systematic increase of the non-linear optical properties is observed every time the closure reaction is induced by a suitable irradiation. The large change of molecular non-linear optical coefficients can be exploited e.g., for the realization of an optical switch. Moreover, we show that also the intrinsic response of the “closed” (i.e., more conjugated) form is, in some case, quite large. The structural reasons of this phenomenon are discussed.

FT-Raman spectra ( λ exc =1064 nm) of two crystalline forms (I and II) of Nolomirole are presented and discussed. Spectral markers characteristic and selective for the two polymorphs are identified. The analysis of Raman spectra obtained from samples made as mechanical mixtures of the two pure polymorphs suggests criteria for developing a spectroscopic method for the determination of the two phases in Nolomirole samples of unknown polymorph composition. On this basis a revision of some published results and conclusions concerning phase transformations occurring in thermally and/or mechanically treated Nolomirole powders is proposed.

Calcium oxalate is found in nature in three different crystalline states determined by the number of H2O in the unit formula (whewellite CaC2O4·H2O, COM; weddellite CaC2O4·(2 + x)H2O, COD and caoxite CaC2O4·3H2O, COT). The properties of these materials are relevant in the field of biomedicine, cultural heritage and mineralogy. In two previous papers, we have used X-ray diffraction and vibrational spectroscopy (infrared and Raman) to derive information on crystal and molecular structures of COM and COD. In this paper, we complete the synthesis and analysis on the third form, COT, and present a comparative study of the data collected from the three crystalline states. The experiments clearly highlight the role played by the H2O molecules linked within the structure by different kinds of hydrogen bonds. The vibrational assignment of the infrared and Raman bands are critically proposed. The fact relevant for the work in biomedicine, cultural heritage and crystallography is that a simple examination of the spectra allows quickly to determine the chemical nature of the material in an unknown sample even in a minute quantity or in awkward experimental conditions.

The Raman spectra of H 2 and D 2 adsorbed on metal–organic framework-5 at various pressures (H 2 : 12.8 and 30.3 bar; D 2 : 2.2–24.5 bar) and temperatures (H 2 : 298 K; D 2 : 40–300 K) have been recorded. The shifts observed in the vibrational modes of the gases indicate that physisorption is responsible for the attractive interactions between the gas and the framework; these interactions are larger with respect to those detected for carbon materials.

The study of the temperature-dependent Raman spectra of n-alkanes from the solid through melting and in the melt phase reveals that short intermolecular correlation can occur in the melt forming at Tm and just above Tm a sizable concentration of extended trans C−C bonds sequences. The mean length of these trans sequences is not less than approximately 5 units. The implications of these observations regarding the mechanism of crystallization of n-alkanes are discussed.

A theoretical investigation is presented aimed to the interpretation of the spectroscopic behaviour of the methoxy group in molecules belonging to the class of hydrofluoroethers. The simulation of infrared and Raman spectra of four different stable conformers of CH 3 –O–CF 2 –CF 2 –O–CH 3 and the comparison with the experimental spectra allow to propose a vibrational band assignment in the CH stretching region. This clarifies the role of the CF 2 group in determining the electronic properties and spectroscopic parameters of methyl CH bonds when back-donation of electronic charge take place from oxygen.

The effect of the confinement of pi electrons in one- and two-dimensional domains is illustrated with several examples ranging from linear polyene chains to planar molecules with honeycomb structure. Theoretical computations and specific Raman experiments on molecular materials demonstrate that a molecular approach provides a unified key to the interpretation of the Raman response both of linear polyconjugated polymers (polyacetylene) and of nanostructured graphitic materials.

The vibrational Infrared and Raman Spectra of a MgCl 2 -TiCl 4 Ziegler-Natta catalyst precursor with a 50/1 MgCl 2 /TiCl 4 ratio have been recorded. The Raman spectrum of this catalyst precursor, in the range 50-500 cm -1 , shows clear scattering lines which can be assigned to the complex MgCl 2 -TiCl 4 , well separated from those of the initial species. Analogous, but less clear signals can be found in the infrared spectrum. Vibrational symmetry analysis and quantum chemical calculations of suitable models of MgCl 2 -TiCl 4 complex have been made for the interpretation of the experimentally recorded spectra. The observed spectroscopic signals can be explained in terms of the existence of only one type of MgCl 2 -TiCl 4 complex where the TiCl 4 molecules are complexed on the MgCl 2 along the (110) lateral cuts in a local C 2v symmetry with the Ti atoms in an octahedral coordination.

The extent of π-electron delocalization in polyconjugated organic materials is the basic molecular structural property required for attaining large molecular hyperpolarizabilities (β, γ) and large nonlinear optical (NLO) response (χ(2), χ(3)). When the electronic and the vibrational contributions to hyperpolarizabilities are considered we have shown that for low band-gap molecules at least the longitudinal βe and γe are as large as βv and γv. Since molecular vibrations (frequencies and intensities in IR and Raman) can be derived both experimentally and theoretically by ab initio methods, the vibrational contributions to β and γ can be obtained from either experimental or calculated IR and Raman spectra and the two values compared. New materials with improved NLO properties need to be devised for a successful breakthrough in technology. We have synthesized low band-gap molecules whose ground electronic state is forced to be quinoid (planarity and the consequent π-electron delocalization should yield large γ values) and its first excited state is aromatic. Very little is known on NLO properties of quinoid systems. All our molecules have been characterized by UV-Vis, 1 H -NMR, FT-IR, FT-Raman and their properties theoretically studied by DFT methods. With this work we try to identify the molecular features which optimize the NLO properties and we find that the vibrational contribution to molecular hyperpolarizability γv (measured from spectra and calculated by quantum chemical methods) and the χ(3) value (experimentally determined by third-harmonic generation, THG) of the quinoid structures are extremely large.

We present a quantum chemical investigation of the vibrational frequencies and Raman intensities of large polycyclic aromatic hydrocarbons (PAHs) as models for nanosized graphitic domains in carbon materials. The gradient corrected BLYP functional, in the framework of density functional theory, was employed to compute equilibrium structures, vibrational force fields, and Raman intensities. Molecules of different size (from 24 to 138 carbon atoms) and symmetry (D6h, D3h, D2h) were investigated. It is shown that the simulated Raman spectra compare well with the available experimental spectra. The analysis of Raman activities in terms of local contributions from internal coordinates shows that the PAHs can be grouped in essentially two classes related more strictly to their “benzenoid” character than to the shape of their periphery. The analysis of local contributions to polarizability derivatives combined with the shape of the molecular motion of the Raman active vibrations in the 1300 cm-1 region of PAHs s...

Here we present, for the first time, an extension of spatially offset Raman spectroscopy to thin (tens of micrometers thick), highly turbid stratified media such as those encountered in paintings. The method permits the non-destructive interrogation of painted layers in situations where conventional Raman microscopy is not applicable due to high turbidity of the top layer(s). The concept is demonstrated by recovering the pure Raman spectra of paint sub-layers that are completely obscured by paint over-layers. Potential application areas include the analysis of paintings in art preservation and restoration avoiding the cross-sectional analysis used currently with this type of samples. The technique also holds promise for the development as a non-destructive subsurface tool for in situ analysis using portable instruments.

This note shows the first results of a study concerning the development of a new method for the consolidation of decayed carbonatic matrices. On the basis of the results achieved with ammonium oxalate, the authors tested a different mechanism to crystallize calcium oxalate phases in calcium carbonate substrate using diethyl oxalate solution. Raman spectroscopy provided a significant analytical support on the study of diethyl oxalate hydrolysis allowing to monitor the reaction and to suppose the occurrence of a reaction intermediate. The investigation of the newly-formed calcium oxalate phases after the reaction of diethyl oxalate with calcite powder allowed to verify the reactivity of the proposed solution and to highlight the crystallization of caoxite, an uncommon calcium oxalate phase.

In this work, we report a comparative analysis of the infrared and Raman spectra of octa(3-hexylthiophene) (3HT)8, trideca(3-hexylthiophene) (3HT)13, and poly(3-hexylthiophene) P3HT recorded in various phases, namely, amorphous, semicrystalline, polycrystalline and single crystal. We have based our analysis on the spectra of the (3HT)8 single crystal (whose structure has been determined by selected area electron diffraction) taken as reference and on the results of DFT calculations and molecular vibrational dynamics. New and precise spectroscopic markers of the molecular structures show the existence of three phases, namely: hairy (phase 1), ordered (phase 2), and disordered/amorphous (phase 3). Conceptually, the identified markers can be used for the molecular structure analysis of other similar systems.

An attractive intermolecular interaction which has been called “halogen bonding” exists between the nitrogen, sulfur, or oxygen atoms present in HC motifs and the iodine atom of PFC residues. The “halogen bonding” is strong enough to overcome the low affinity existing between PFC and HC compounds, driving their self-assembly into supramolecular architectures. The non-covalent co-polymer formed by 1,2-diiodotetrafluoroethane with diazabicyclooctane has been prepared and characterised by FT–IR and –Raman spectroscopies. We propose the changes shown by the vibrational spectra of single PFC and HC components when involved in halogen bonded co-polymers as diagnostic probes of the interaction and as tools to rank the electron-donor ability of differently heteroatom substituted hydrocarbons.

A valence force field based on H\"uckel's theory has been developed, which allows us to establish a close correlation between phonons of graphite and the normal modes of small polycyclic aromatic hydrocarbons (such as coronene and hexabenzocoronene). The results show that in these systems two kinds of motions dominate the Raman spectrum: the \cyrchar\CYRYA{} mode and the ``breathing'' A mode. These modes are the equivalent, in a finite domain, of the ${E}_{2g}$ phonon of graphite at the \ensuremath{\Gamma} point and the ${A}^{\ensuremath{'}}$ phonon at the K point of the first Brillouin zone. This study provides a useful basis for the understanding of the Raman spectra of any material containing ${\mathrm{sp}}^{2}$ carbon domains.

In this article we focus on the conformational dependence of molecular hyperpolarizabilities and on the related infrared and Raman intensities for molecules where π electron delocalization and/or back-donation by oxygen lone pairs can occur. Ab initio calculations at the Hartree–Fock level have been performed on anisole and 4-nitro-anisole with 3-21G and 6-31G∗∗ basis sets. Vibrational properties and second and third order molecular polarizabilities have been studied as a function of the torsional angle describing the rotation of the O–(CH3) group about the φ-O bond. In these systems two competing effects can take place, namely back-donation and conjugation. From the study of infrared intensities it is shown that no back-donation of electrons from the oxygen lone pairs takes place, independently of the conformation of the methoxy-group. These results are used in the interpretation of the infrared spectrum of many compounds which show a characteristic strong and low frequency infrared CH stretching vibration, previously assigned to a back-donation effect. However, conjugation dependent optical properties, such as the vibrational pattern, the intensity of the collective modes, the first (β) and second order (γ) hyperpolarizabilities are almost constant with respect to changes of the torsional angle.

Molecular properties of oligo-para-phenylenes are determined mostly by the combined effect of π electron delocalization and intra-ring confinement. In order to study their relative role, we have carried out an ab initio study on biphenyl and terphenyl. Energies of formation, geometrical parameters, vibrational spectra and molecular hyperpolarizabilities are studied (using the 3-21G basis) as function of the torsional angle between two adjacent rings and the number of rings in the molecule. Relaxation contribution to first- and second-order hyperpolarizabilities (βr and γr, respectively) are obtained with a vibrational method from computed frequencies, infrared and Raman intensities. Raman lines of Я-containing normal modes progressively weaken when the systems are distorted. Similarly the component of γr along the chain axis (γzzzzr) and the orientation average 〈γr〉 decrease. For planar molecules, Raman intensities and molecular hyperpolarizabilities show a superlinear dependence upon the number of rings in the chain, while when adjacent rings lie on perpendicular planes an almost linear dependence is obtained. The optical properties of the para-phenylenes studied can be predicted by the simple addition of the corresponding values for the repeating unit (benzene) only in the conformationally distorted case. This fact suggests that in the planar case the effects of π electron delocalization are much stronger than those of the intra-ring confinement potential. The comparison with experimental determinations of 〈γr〉 offers clear evidence that in solution oligo-p-phenylenes are highly conformationally distorted. An improvement of molecular properties is thus predicted if torsions about inter-ring bonds are hindered by proper substitutions or bridging.

Using data from computed observables of vibrational spectroscopy (frequency, infrared, Raman and hyper Raman intensities) we derive structural criteria necessary to design new organic conjugated molecules with enhanced non linear optical responses. In this work, in particular, we focus on second order hyperpolarizability (γ) and extract from our analysis the structural requirements necessary to reach large negative γ values.

A new polyconjugated polymer, poly(indenofluorene), has been studied with vibrational spectroscopy. The Raman spectrum shows a few bands with extraordinary high absolute intensity associated with the extended delocalization of the π electronic system. A vibrational method has been applied to determine the relaxation contribution to the second order hyperpolarizability γ r . The combination of a large measured value of γ r (3.75 × 10 −33 esu per repeating unit) with the low band gap, the high stability and solubility, makes poly(indenofluorene) a promising material for technological applications

The study of temperature dependent infrared (i.r.) and Raman spectra of alternating ethylenetetrafluoroethylene (ETFE) copolymer suggests that the transition from orthorhombic to hexagonal phases may be driven by the generation and propagation of conformational solitons (gentle mobile chain twist).

It is shown that molecular non linear optical properties can be measured with the vibrational infrared and Raman spectra. Correlations between optical non linearities and structural features are discussed.

Raman spectra of oligo-p-phenylenes, oligorylenes, and oligoacenes of different chain lengths have been obtained in the solid state and in solution. Among the properties studied, particular attention is devoted to frequency and intensity dispersion of the Raman bands with increasing conjugation length and to the vibrational second order hyperpolarizability γ r. The results obtained are compared with those relative to polyenic systems. The behavior of the various classes of molecules studied is in some cases different both in absolute values and trends. This fact is discussed in order to clarify the influence of the topology of the π-electron system on the properties of conjugated materials and to determine whether the presence of aromatic rings in the main chain can confine π electrons and so reduce delocalization. Oligorylenes turn out to be the compounds with the largest vibrational γ r. The results also indicate that absolute Raman intensity shows strong intensity dispersion with conjugation length and...

The aim of this work is to understand the molecular structural properties which may justify the great observed stability of doped alkoxy polythiophenes. Infrared frequency and intensity spectroscopy and Raman spectroscopy are used as probes. Suitably synthesized oligomers with increasing chain length and preassigned chemical structure have been studied together with several model molecules. The existence of through‐space and through‐bond S‐ ‐ ‐O interactions has been revealed. The extent of the topologically dependent perturbation induced by the charge injection by the oxygen atoms is detected and measured. The inter‐ and intraring delocalizations have been monitored by the observation of the softening of the strongly Raman active ‘‘amplitude mode’’ and by the red shift of the electronic spectra. The conformation of the side chains is trans planar in the solid state and collapses in a liquidlike premelting state before the melting of the crystal.

The vibrational infrared and Raman spectra of a series of t‐butyl substituted oligomers of para‐phenylenevinylene and of the corresponding polymer in the pristine and potassium‐doped states have been recorded for the first time and interpreted on the basis of the theory of the effective conjugation coordinate. The Raman spectra of selectively deuteriated materials have also been analyzed. Evidence is found of strong phonon confinement. The information derived from the spectra is that the charge carrier is confined over a few monomer units and that when the polymer is doped with electron donors the benzene ring is preferentially perturbed. The data collected in this work are compared with the results from UV spectroscopy and ESR experiments which indicate a larger dimension of the charge carrier. The information which can be derived by using in a complementary way the data from these spectroscopies are presented and discussed.

Because of the peculiar physics of polyconjugated molecules, the spectroscopic properties (infrared and Raman) can reflect with great detail the molecular properties of such materials. The vibrational spectra then become a unique tool for the molecular characterization of the materials in their pristine and doped state or when they are made to interact with additional guest molecules. In this paper we describe the effect, at the molecular level, of the inclusion of proteins (glucose oxidase and peroxidase) in films of host materials of the class of polythiophenes (in the doped state). Care was taken to keep the biological activity of the enzyme (guest) at a very reasonable level, even when embedded in the polymer host matrix. This study is aimed at contributing to the development of science and technology of novel devices in the field of bioelectronics, in which the polyconjugated material is used as an interface between the active enzyme and the inorganic moiety which elaborates the signal.

Chain-length-dependent π electron delocalization is analyzed in pristine oligofurans and polyfuran by means of Fourier transform Raman spectroscopy. Neutral polyfuran shows a large frequency dispersion with conjugation length and it has not yet reached saturation at the level of the hexamer. In spite of such a large π electron delocalization the polymer seems to show an unexpectedly good stability in air at room temperature. Regio-defined poly(2,5-difurans) could be good candidates for technological developments.

Using a recently developed method, we show here that solvent effects on the first molecular hyperpolarizabilities of push‐pull polyenes can be predicted by evaluation of the relaxation contribution βr to the hyperpolarizability from vibrational infrared and Raman intensities and vibrational frequencies. The molecules studied in this work are a few organic polymethine dyes with different donor and acceptor groups. The analysis of their vibrational spectra confirms the key role played by the structural parameters of the polyene chain in determining the nonlinear optical response.

Micro resonance Raman spectra of a series of synthetic carotenoids and of a large number of bird's feathers which contain various kinds of carotenoids were analysed on the basis of the effective conjugation coordinate (ECC) theory. The data obtained on parrots provide the first structural data on the chemical nature of the pigments embedded in their feathers, and show that these pigments are unmethylated polyene molecules. Data on the molecular orientation of the carotenoids and on the presence of different pigments in the same feather are presented and discussed.

This study is focused on the characterization of the oxalate films observed on the surfaces of several ancient monuments. They consist mostly of calcium oxalate in the common forms, namely whewellite (CaC2O4 • H2O) and weddellite (CaC2O4 • (2 + x) H2O), which chemically differ only by the number of water molecules contained in the crystalline unit cell. In order to ascertain the controversial origin of the calcium oxalate films, the settlement of their mineralogical composition and stratigraphy is essential. Because of the lack of analytical techniques able to discriminate, with an acceptable resolution, between whewellite and weddellite in cross-sections, in the literature, very little attention has been paid to these data. μ-Raman mapping allowed for the first time, to unequivocally identify the phases which occur in the calcium oxalate films and to obtain direct information, at high spatial resolution, on their distribution with respect to the material surface. μ-Raman mapping carried out on polished cross-sections of samples belonging to the facade of the Cathedral of Trento showed, for a yet unknown reason, either a random distribution of the two phases or a higher content of weddellite in the external portions of the calcium oxalate films. Meaningful differences in the mineralogical composition have been highlighted between areas of the monument sheltered from rainfall and those exposed to rainfall. A multivariate approach using principal components analysis has been used to analyze the huge number of spectra in the Raman maps. Copyright © 2012 John Wiley & Sons, Ltd.

Apomorphine is a well-known short-acting dopamine agonist typically used in the treatment of patients with advanced Parkinson's disease. In this work we propose a method for detection of apomorphine in blood plasma through Surface Enhanced Raman Scattering (SERS) technique. Detection can be achieved in a few minutes by simply depositing a drop of the blood plasma containing Apofin ® on silica Thin Layer Chromatography (TLC) substrates and dropping the silver colloid on it. The Raman measurements carried out on the edges of the stain reveal the presence of the drug through its SERS signal which is found to significantly differ from the normal Raman spectrum. We propose a Density Functional Theory (DFT) model for the interpretation of the major SERS signatures of apomorphine in terms of the interaction of the drug molecule with silver.

The temperature-dependent vibrational infrared and Raman spectra of 20% solutions of decylammonium chloride in H2O (D2O) were studied. According to previous work, phases SI and SII were identified in the low-temperature range. Molecular and supermolecular structures were derived. The upper shift (Δν = 12 cm−1) of the Raman-active antisymmetric stretching CH2 mode (d−) and its narrowness are peculiar and specific signals of a specific structure. It is proposed that the phase transition SI SII is originated by the onset of a conformational flexibility generally described as twistons or conformational solitons. No evidence was found that the alkyl residues have librational freedom about their axes.

Frequency and intensity spectroscopies have been used in the reanalysis of the vibrational spectrum (IR and Raman) of alternate copolymers of ethylene and tetrafluoroethylene. A new assignment of the CH stretching fundamental is proposed. The seeming anomalies of the infrared spectrum in the CH stretching range are accounted for in terms of equilibrium atomic charges and charge fluxes. In particular, the analysis of the dichroic ratios shows that there exists a relevant mobility of the electronic charge along the C-C bonds