Scaling of Computed Cyano-Stretching Frequencies and IR Intensities of Nitriles, Their Anions, and Radicals

Stoyanov, Simeon

doi:10.1021/jp908400g

Cited by 14 publications

(8 citation statements)

References 89 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Hence, µ b j ′ values determined by DFT can be scaled to reproduce experimental intensities if available. 66 Since measurements of the absolute IR intensities of vibrational transitions in DMABN's CT state have not been measured, the scaling factor is unknown, and we will need to instead compare the relatiVe magnitude of solvent induced Stokes shift in the ν 8a and ν CN .…”

Section: Resultsmentioning

confidence: 99%

“…Third-order force constants and anharmonic couplings determined by DFT have been shown to accurately reproduce the vibrational spectrum of several molecules. ,,− However, dipole derivatives are still poorly quantified by DFT calculations, though the relative intensities of different transitions can be quite accurate. Hence, μ⃗ j ′ values determined by DFT can be scaled to reproduce experimental intensities if available . Since measurements of the absolute IR intensities of vibrational transitions in DMABN’s CT state have not been measured, the scaling factor is unknown, and we will need to instead compare the relative magnitude of solvent induced Stokes shift in the ν 8a and ν CN .…”

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Probing the Charge Transfer Reaction Coordinate of 4-(Dimethylamino)benzonitrile with Femtosecond Stimulated Raman Spectroscopy

2010

View full text Add to dashboard Cite

Femtosecond stimulated Raman spectroscopy (FSRS) and femtosecond transient absorption have been used to probe the photoinduced charge transfer (CT) dynamics of 4-(dimethylamino)benzonitrile in methanol and n-hexane. Through a combined analysis of temporal changes in the Raman modes and transient absorption kinetics, a more complete picture of the reaction coordinate of the intramolecular charge transfer process has been established. FSRS spectra of the phenyl C═C stretching mode (Wilson mode 8a) at 1607 cm(-1), which shifts to 1581 cm(-1) in the CT state, and transient absorption measurements ranging from 360 to 700 nm support internal conversion from the locally excited to the charge transfer state in 4-5 ps and then a subsequent vibrational relaxation within the CT state manifold on a 6-8 ps time scale. Dramatic shifting and narrowing of the 1581 cm(-1) quinoidal C═C stretch (ν(8a)) on the ∼7 ps time scale indicates that the quinoidal distortion is an important probe of the CT reaction dynamics. The cause of the spectral shifts is determined by comparing the observed shifts in the vibrational spectrum to anharmonic couplings computed for the benzonitrile radical anion by density functional theory (DFT) and with quantitative theoretical models of the solvent induced vibrational peak shifts. The DFT calculations indicate that the 10 cm(-1) downshift of the C═C stretch is most likely attributable to significant vibrational excitation in nontotally symmetric modes that are strongly anharmonically coupled to the C═C stretch.

show abstract

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Probing the Charge Transfer Reaction Coordinate of 4-(Dimethylamino)benzonitrile with Femtosecond Stimulated Raman Spectroscopy

2010

View full text Add to dashboard Cite

show abstract

“…Extensive investigation into the spectroscopic shifts of nitrile vibrations has established that the nitrile frequency is primarily influenced by its position on the aromatic ring and electron donating character of the ring. − More recent studies by Zhao and Han dealing specifically with DMABN have given a possible reassignment of the HICT and “free” nitrile frequencies previously assigned by Kwok . Using DFT calculations, Zhao and Han showed that hydrogen bonding to the nitrile actually up-shifts the nitrile frequency in DMABN.…”

Section: Discussionmentioning

confidence: 99%

Multimode Charge-Transfer Dynamics of 4-(Dimethylamino)benzonitrile Probed with Ultraviolet Femtosecond Stimulated Raman Spectroscopy

2012

View full text Add to dashboard Cite

4-(Dimethylamino)benzonitrile (DMABN) has been one of the most studied photoinduced charge-transfer (CT) compounds for over 50 years, but due to the complexity of its excited electronic states and the importance of both intramolecular and solvent reorganization, the detailed microscopic mechanism of the CT is still debated. In this work, we have probed the ultrafast intramolecular CT process of DMABN in methanol using broad-band transient absorption spectroscopy from 280 to 620 nm and ultraviolet femtosecond stimulated Raman spectroscopy (FSRS) incorporating a 330 nm Raman pump pulse. Global analysis of the transient absorption kinetics revealed dynamics occurring with three distinct time constants: relaxation from the Franck-Condon L(a) state to the lower locally excited (LE) L(b) state in 0.3 ps, internal conversion in 2-2.4 ps that produces a vibrationally hot CT state, and vibrational relaxation within the CT state occurring in 6 ps. The 330 nm FSRS spectra established the dynamics along three vibrational coordinates: the ring-breathing stretch, ν(ph), at 764 cm(-1) in the CT state; the quinoidal C═C stretch, ν(CC), at 1582 cm(-1) in the CT state; and the nitrile stretch, ν(CN), at 2096 cm(-1) in the CT state. FSRS spectra collected with a 400 nm Raman pump probed the dynamics of the 1174 cm(-1) CH bending vibration, δ(CH). Spectral shifts of each of these modes occur on the 2-20 ps time scale and were analyzed in terms of the vibrational anharmonicity of the CT state, calculated using density functional theory. The frequencies of the δ(CH) and ν(CC) modes upshift with a 6-7 ps time constant, consistent with their off-diagonal anharmonic coupling to other modes that act as receiving modes during the CT process and then cool in 6-7 ps. It was found that the spectral down-shifts of the δ(CH) and ν(CN) modes are inconsistent with vibrational anharmonicity and are instead due to changes in molecular structure and hydrogen bonding that occur as the molecule relaxes within the CT state potential energy surface.

show abstract

“…Solvent and coordination effects. The sensitivity of cyano group stretching vibrations to the surrounding is well documented 26 and has frequently been used to study ion-ion and ion-solvent interactions. 11,[27][28][29][30][31] Here, at B2200 cm À1 , the n(C3-N2) signature of TDI varies over 14 cm À1 between electrolytes (Fig.…”

Section: Experimental Raman Spectra Of Litdi Electrolytesmentioning

confidence: 99%

Ion–ion and ion–solvent interactions in lithium imidazolide electrolytes studied by Raman spectroscopy and DFT models

Scheers¹,

Niedzicki²,

Żukowska³

et al. 2011

Phys. Chem. Chem. Phys.

View full text Add to dashboard Cite

Molecular level interactions are of crucial importance for the transport properties and overall performance of ion conducting electrolytes. In this work we explore ion-ion and ion-solvent interactions in liquid and solid polymer electrolytes of lithium 4,5-dicyano-(2-trifluoromethyl)imidazolide (LiTDI)-a promising salt for lithium battery applications-using Raman spectroscopy and density functional theory calculations. High concentrations of ion associates are found in LiTDI:acetonitrile electrolytes, the vibrational signatures of which are transferable to PEO-based LiTDI electrolytes. The origins of the spectroscopic changes are interpreted by comparing experimental spectra with simulated Raman spectra of model structures. Simple ion pair models in vacuum identify the imidazole nitrogen atom of the TDI anion to be the most important coordination site for Li(+), however, including implicit or explicit solvent effects lead to qualitative changes in the coordination geometry and improved correlation of experimental and simulated Raman spectra. To model larger aggregates, solvent effects are found to be crucial, and we finally suggest possible triplet and dimer ionic structures in the investigated electrolytes. In addition, the effects of introducing water into the electrolytes-via a hydrate form of LiTDI-are discussed.

show abstract

Scaling of Computed Cyano-Stretching Frequencies and IR Intensities of Nitriles, Their Anions, and Radicals

Cited by 14 publications

References 89 publications

Probing the Charge Transfer Reaction Coordinate of 4-(Dimethylamino)benzonitrile with Femtosecond Stimulated Raman Spectroscopy

Probing the Charge Transfer Reaction Coordinate of 4-(Dimethylamino)benzonitrile with Femtosecond Stimulated Raman Spectroscopy

Multimode Charge-Transfer Dynamics of 4-(Dimethylamino)benzonitrile Probed with Ultraviolet Femtosecond Stimulated Raman Spectroscopy

Ion–ion and ion–solvent interactions in lithium imidazolide electrolytes studied by Raman spectroscopy and DFT models

Contact Info

Product

Resources

About