Stefano Radice

Infrared and Raman analyses of the halogen-bonded non-covalent adducts formed by α,ω-diiodoperfluoroalkanes with DABCO and other electron donors

Abstract 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.

Joint experimental and computational investigation of the structural and spectroscopic properties of poly(vinylidene fluoride) polymorphs.

State-of-the-art density functional theory calculations are here adopted for the investigation of the crystal structure and of the vibrational properties of α, β, γ, and δ phases of poly(vinylidene fluoride) (PVDF), in comparison with IR and Raman measurements. DFT calculations allowed a detailed interpretation of the IR and Raman spectra of α and β phases, giving vibrational assignments useful for qualitative and quantitative characterization of these systems. From a molecular perspective, the computational investigation of the crystal structure and the spectra of PVDF polymorphs helped in clarifying the role of supramolecular dipole-dipole interactions, which indeed modulate the vibrational properties of these systems, indicating also that intermolecular interaction could play a significant role in the modulation of ferroelectric properties. Furthermore, the combined experimental and computational approach allowed us to identify and characterize the thermally and mechanically induced γ phase, shedding light on the far-IR marker bands of this elusive phase of PVDF.

Quantum Mechanical Calculations and Spectroscopic Analysis of Fluorinated Vinyl Ether Molecules

Abstract Infrared spectroscopy in connection with quantum mechanical calculations based on density functional theory (DFT) method have been used for the characterization of fluorinated vinyl ethers. A good correspondence between experimental and calculated spectra has been found. The peculiar behaviour in terms of frequency and intensity parameters relative to the CC stretching normal mode along a series of related compounds has been analysed and interpreted in terms of atomic polar tensor (APT) and equilibrium charge and charge fluxes (ECCFs) models. This study indicates that the IR intensity of the CC stretching mode is almost completely due to the flux terms, suggesting that the presence of fluorine atoms make the charge along CC bond very mobile. This approach, based on comparative analysis of experimental and theoretical data, allows a critical comparison between various chemically related molecules and provides information on the various effects of chemical substitution on the molecular charge distribution.

Colorimetric Detection of Perfluorinated Compounds by All-Polymer Photonic Transducers

We report on the highly sensitive optical and colorimetric detection of perfluorinated compounds in the vapor phase achieved by all-polymer dielectric mirrors. High optical quality and uniformly distributed Bragg reflectors were fabricated by alternating thin films of poly(N-vinylcarbazole) and Hyflon AD polymers as high and low refractive index medium, respectively. A new processing procedure has been developed to compatibilize the deposition of poly(N-vinylcarbazole) with the highly solvophobic Hyflon AD polymer layers to achieve mutual processability between the two polymers and fabricate the devices. As a proof of principle, sensing measurements were performed using the Galden HT55 polymer as a prototype of the perfluorinated compound. The Bragg stacks show a strong chromatic response upon exposure to this compound, clearly detectable as both spectral and intensity variations. Conversely, Bragg mirrors fabricated without fluorinated polymers do not show any detectable response, demonstrating that the Hyflon AD polymer acts as the active and selective medium for sensing perfluorinated species. These results demonstrate that organic dielectric mirrors containing perfluorinated polymers can represent an innovative colorimetric monitoring system for fluorinated compounds, suitable to improve both environmental safety and quality of life.

Static vs dynamic DFT prediction of IR spectra of flexible molecules in the condensed phase: The (ClCF2CF(CF3)OCF2CH3) liquid as a test case

First-principles molecular dynamics (FPMD) simulations in the framework of Density Functional Theory (DFT) are carried out for the prediction of the infrared spectrum of the fluorinated molecule ClCF2CF(CF3)OCF2CH3 in liquid and gas phase. This molecule is characterized by a flexible structure, allowing the co-existence of several stable conformers, that differ by values of the torsional angles. FPMD computed spectra are compared to the experimental ones, and to Boltzmann weighted IR spectra based on gas phase calculations.

FT-IR and NMR studies on the sequence distribution in the alternating copolymers ethylene(E)-tetrafluoroethylene (TFE) and ethylene(E)-chlorotrifluoroethylene (CTFE)

Abstract We have developed an IR method to study the content of monomer sequences in ETFE and ECTFE copolymers that may substitute for NMR spectroscopy in routine analysis. Indeed, the NMR analyses are carried out at 300 °C and 200 °C respectively, risking instrumental damage due to the high temperature. The search for a different technique based only on FT-IR spectroscopy can thereby be justified. We examined NMR and IR spectra of several ETFE and ECTFE polymers with different ethylene molar contents. Combining 19 F NMR and elemental analysis data it was possible to determine the structure of ETFE copolymers at the level of monomer triads. The triad monomer distribution can be obtained in the same way for ECTFE copolymers. In this case it was also possible to obtain 1 H NMR spectra that can be used to determine the concentration of [E]n sequences directly. In the case of ETFE copolymers this could only be calculated by difference. The IR spectra of both copolymers were carefully analyzed in the CH stretching region, because the CH oscillators are very sensitive to sequence distribution (both for frequency and intensity). The information so obtained considers total ethylene sequences [E]n for n>2. Some weak absorptions in the IR spectrum of the ETFE copolymer due to triad sequences [L.N. Pirozhnaya and L. I. Tarutina, Zh. Prikl. Spektros., 34 (1980) 862; L. I. Tarutina, Zh. Prikl. Spektros., 8 (1968) 653] have been correlated with the corresponding triad content determined through NMR spectroscopy. This work allowed us to discriminate in terms of homogeneity of monomer distribution between copolymers of similar molar composition and to test the reliability of available reactivity ratios.