Self-Aggregation in Pyrrole:  Matrix Isolation, Solid State Infrared Spectroscopy, and DFT Study

Abstract

Pyrrole (C 4 H 5 N) was embedded in low-temperature solid inert matrixes (argon, xenon; T ) 9 K) and both the monomer and low-order aggregates characterized by FTIR spectroscopy. The spectroscopic studies were complemented by extensive theoretical [DFT(B3LYP)/6-311++G(d,p)] structural and vibrational studies carried out for the monomer and their self-aggregates (up to four units). The calculated spectrum for monomeric pyrrole fits well those obtained immediately after deposition (at 9 K) of diluted matrixes, which can be prepared keeping the compound at low temperature before deposition and using low fluxes of the sublimate. Annealing of the matrixes to higher temperatures or increasing of the gaseous flux during deposition leads to aggregation, which can be easily recognized spectroscopically. On the basis of the theoretically predicted spectra for the monomer, dimer, trimers, and tetramers of pyrrole, assignments were proposed for the experimentally observed bands. It was also found that the formation of the hydrogen-bonded clusters shows a significant cooperativity effect, which was studied in detail and could be related with several structural and spectroscopic parameters. Infrared spectra of the pure solid compound at low temperatures in both amorphous and crystalline states were also studied and interpreted.

Ab initioquantum dynamical study of the multi-state nonadiabatic photodissociation of pyrrole

“…The optimized S 0 structural parameters are given in Table S1 (supplementary material 41 ). Our computed ground state equilibrium geometry agrees well with available experimental data 42 as well as high level density functional theory (DFT) calculations, 43 the typical (maximum) deviation from experiment being 0.005 Å (0.014 Å) for the bond lengths and 0.2 • (0.4 • ) for the bond angles. The frequencies are collected in Table II, to be discussed below.…”

Experimental and theoretical study of the pyrrole cluster photochemistry: Closing the πσ* dissociation pathway by complexation

“…50. The structure of pyrrole clusters in the ground state has recently been addressed by several groups, e.g., Ref.…”

Quantum Chemical Investigations of Structural Parameters of PVDF-based Organic Ferroelectric Materials

“…Quantum mechanics (QM) methods, which we also denote as QCC (Quantum Chemical Calculations) can provide valuable information about the electronic and structural phase transitions for several polymer backbones giving an insight into structure-property relationships, which are not yet completely elucidated (Broahurst et al 1978;Jungnickel, 1999;Tashiro et al, 1988;Casalini & Roland, 2001;Gao & Scheinbeim, 2000;Casalini & Roland, 2002;Nicholas, 1997;Nicholas et al, 1991;Gómez-Zaravaglia & Fausto, 2004;Teunissen et al, 1994;Sierra, 1993;Evleth et al, 1994;Das & Whittenburg, 1999). Therefore, the first principles-based materials models are helpful for the design of materials with improved properties.…”

“…In this concern, QCC together with experimental techniques have reached widespread application as a tool for characterization of a reactive system and spectra modeling (Nicholas, 1997). The experimental spectroscopic results are often confronted with theoretical calculations in which the vibrational frequencies are computed and afterwards analyzing the corresponding mode in order to reproduce the model molecule characterization (Nicholas et al, 1991;Gómez-Zaravaglia & Fausto, 2004). Moreover, it is possible to make a model of a solid crystalline system or instead be treated as a molecule, depending on the properties that we wish to obtain.…”