Infrared Electroabsorption Spectroscopy of N,N-Dimethyl-p-nitroaniline in Acetonitrile/C₂Cl₄: Solvation of the Solute and Self-Association of Acetonitrile

Abstract

Solvated structures of N,N-dimethyl-p-nitroaniline (DMPNA), an analog of p-nitroaniline (PNA), and self-associated structures of acetonitrile (ACN) in mixed solvents of ACN and C(2)Cl(4) were studied using infrared (IR) electroabsorption and FTIR spectroscopies. IR electroabsorption spectroscopy measures changes in IR absorption intensity upon application of external electric field modulation, which are a sensitive probe for permanent dipole moments. In ACN/CCl(4), PNA has been shown to occur as two distinct solvated forms, namely, 1:1 and 1:2 forms, which have one and two ACN molecule(s), respectively, associated with PNA. The IR electroabsorption and FTIR measurements on DMPNA show that, unlike PNA, DMPNA occurs as a monomer in ACN/C(2)Cl(4) rather than as specific solvated structures analogous to the 1:1 and 1:2 forms because of the substitution effect. Not only does the N,N-dimethyl substitution in DMPNA hamper solvation of ACN at the N(CH(3))(2) group, but it also indirectly blocks strong interactions with ACN at the NO(2) group. Furthermore, by using the ΔA signal of DMPNA as an internal intensity standard, it was found that the dipole moment of ACN in the DMPNA/ACN/C(2)Cl(4) system is about 1.5 times larger than that of the ACN monomer in dilute CCl(4) solution. This large value of the dipole moment in the solution studied here is attributable to the formation of a head-to-tail linear dimer of ACN, whereas the antiparallel dimer is energetically more favorable in the gas phase.

Voltage-induced Infrared Absorption from a Spin-cast Thin Film of Ferroelectric Poly(vinvlidene fhioride-co-trifluoroethvlene) (P(VDF-TrFE))

“…On the other hand, the original spectrum was large for a reoriented sample with respect to the external electric field. 9 Thus, it is reasonable to consider that the observed original spectra at -0.57, -1.3, and -3.0 MV/cm are likely to be caused by the reorientation of polymer chains.…”

“…External electric field effects on the infrared spectra of materials give rise to the vibrational Stark effect, [1][2][3][4] orientation polarization in solutions [5][6][7][8][9] and ferroelectric solids, [10][11][12][13][14][15][16] as well as other effects. In previous work, we demonstrated that the voltage-induced infrared spectra from organic field-effect transistors are due to the carriers generated in organic semiconductors by the field effect.…”

Anharmonic coupling of the CH-stretch and CH-bend vibrations of chloroform as studied by near-infrared electroabsorption spectroscopy

“…The first response we consider is orientational polarization, 17,18,33,34 which is the primary concern in this paper. When liquid molecules having nonzero permanent dipole moment are subject to an external electric field, a small fraction of the molecules tend to align so that the dipole moment is parallel to the applied field.…”

“…8] and needs to be separated. Assuming that the transition hyperpolarizability is negligible 39,40 (i.e., B = 0) and that the reorientation of the molecules through α and A is small compared with that through μ, 18 we have the electronic polarization contribution to the zeroth-derivative A signal of the form…”

“…Here, we present NIR electroabsorption (EA) spectroscopy as a novel experimental approach to study anharmonic vibrational coupling in liquids and solutions through determination of the direction of the transition moment with respect to the permanent dipole moment of the molecule. By integrating a high-throughput NIR spectrometer used in our nanosecond time-resolved IR experiments [14][15][16] into an existing MIR EA apparatus, 17,18 we extend EA spectroscopy to cover the NIR region so that the electric-field effects on combination bands and overtones can be studied. In the present study, we focus on the combination band of the CHstretching (ν 1 ) mode at 3019 cm −1 and doubly degenerate CH-bending (ν 4 ) mode at 1215 cm −1 of liquid chloroform (see Fig.…”