Structure and hydrogen bond vibrations of the jet-cooled 1:1 complex between 7-azaindole and formamide: A laser-induced fluorescence spectroscopy study

Hazra, Montu K.; Mukherjee, Moitrayee; Goswami, Debabrata; Chakraborty, Tapas

doi:10.1016/j.cplett.2011.01.019

Cited by 7 publications

(8 citation statements)

References 30 publications

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“…66 Chakraborty and co-workers found an intermolecular vibrational mode at 86 cm −1 , as well as 28, 47, 56, and 148 cm −1 modes and combination band at 114 cm −1 , of AI−formamide cluster in the gas phase by laser-induced fluorescence spectroscopy. 67 Therefore, it is natural to think that the broad band at ca. 80 cm −1 for AI in acetone, CH 3 CN, and DMSO is attributed to intermolecular HB vibrations involving the solvent.…”

Section: ■ Materials and Methodsmentioning

confidence: 99%

Solvent Dependence of 7-Azaindole Dimerization

2013

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We have investigated 7-azaindole (AI) in a variety of solvents including CCl4, CHCl3, CH2Cl2, acetone, CH3CN, and DMSO by femtosecond Raman-induced Kerr effect spectroscopy. In differential low-frequency Kerr spectra between the solutions and the respective neat solvents, vibrational bands of the AI hydrogen-bonding (HB) dimer have been observed at ca. 90 and 105 cm(-1) in CHCl3 and CH2Cl2, as well as CCl4: the standard solvent for the AI dimer. In contrast, a broad monomodal band at ca. 80 cm(-1) characterizes an HB mode between the AI monomer and solvent in acetone, CH3CN, and DMSO. The overdamped Kerr transients in the picosecond region show evidence of both the AI monomer and dimer reorientations in CHCl3, CH2Cl2, acetone, and CH3CN, but only the monomer reorientation has been confirmed in DMSO. The clear intermolecular HB bands have not been observed in acetone, CH3CN, and DMSO because these solvents are sufficiently strong HB acceptors, which form HB AI-solvent complexes, thus preventing quantitative AI dimerization. In addition, it is plausible that the HB band of between AI and solvent obscures the intermolecular bands of the AI dimer when the concentration of the AI dimer is much lower than the AI monomer. For comparison, we have employed NMR to study the concentration-dependent chemical shift of the proton attached to the N at the 7-position of AI and to estimate the dimerization constant: 356, 13.3, 14.7, 0.727, and 0.910 M(-1) in CCl4, CHCl3, CH2Cl2, acetone, and CH3CN, respectively. The femtosecond Raman-induced Kerr effect spectroscopy and NMR results are in good agreement.

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Section: ■ Materials and Methodsmentioning

confidence: 99%

Solvent Dependence of 7-Azaindole Dimerization

2013

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“…Recently, we also studied the LIF spectroscopy of jet-cooled 7AI•••formamide and 7AI•••pyrrolidinone complexes. 35,23 However, in both cases, only UV fluorescence from the locally excited state was detected.…”

Section: ■ Results and Discussionmentioning

confidence: 94%

“…Thus, the photophysics of the complex is sensitively medium dependent, which is not the case for the homodimer. Recently, we also studied the LIF spectroscopy of jet-cooled 7AI···formamide and 7AI···pyrrolidinone complexes. , However, in both cases, only UV fluorescence from the locally excited state was detected.…”

Section: Resultsmentioning

confidence: 99%

Excited State Tautomerization of 7-Azaindole in a 1:1 Complex with δ-Valerolactam: A Comparative Study with the Homodimer

2012

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A comparative analysis for relative stability between normal and tautomeric forms in the excited electronic states of 7-azaindole···δ-valerolactam 1:1 complex and 7-azaindole homodimer has been presented. The tautomeric configuration of the complex is estimated to be ~6 kcal/mol more stable than normal form, and the same for homodimer appears to be ~10 kcal/mol. Consistent with these estimates both the complex and homodimer undergo facile double proton transfer tautomerization upon UV excitation in hydrocarbon solutions (Chou; et al. J. Am. Chem. Soc. 1995, 117, 7259). However, we notice that such similarity in photophysical behavior of the two hydrogen-bonded systems is lost completely in a cold supersonic jet expansion. The jet-cooled homodimer emits only the tautomer fluorescence in the visible spectral region, but the complex emits exclusively from the locally excited state in ultraviolet. We have interpreted this contrast by arguing that the effective barrier for excited state double proton exchange tautomerization of the complex is larger compared to that of the homodimer, and the difference originates because of asymmetric nature of the two hydrogen bonds of the complex.

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“…The effect of intermolecular vibrations present in the dimer on the intramolecular modes of the excited 7-azaindole monomer moiety in the dimer has been reported recently for the 7-azaindole 3 3 3 formamide dimer. 63 Specific types of low frequency intermolecular vibrations are very often observed in the electronic spectrum of the dimer, especially when they are double hydrogen bonded. 45 The remaining bands apart from the assigned intramolecular vibrations of the excited monomer unit (7-azaindole) of the dimer observed in Figure 1b could be due to either low frequency intermolecular vibrations or the presence of isomeric structures of the dimer.…”

Section: Resultsmentioning

confidence: 99%

Structure of 7-Azaindole···2-Fluoropyridine Dimer in a Supersonic Jet: Competition between N–H···N and N–H···F Interactions

et al. 2011

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In the present work, we have investigated the structure of 7-azaindole···2-fluoropyridine dimer in a supersonic jet by employing resonant two photon ionization (R2PI), IR-UV, and UV-UV double resonance spectroscopic techniques combined with quantum chemistry calculations. The R2PI spectrum of the dimer is recorded by electronic excitation of the 7-azaindole moiety, and a few low frequency intermolecular vibrations of the dimer are clearly observed in the spectrum. The electronic origin band of the dimer is red-shifted by 1278 cm(-1) from the S(1) ← S(0) origin band of 7-azaindole monomer. The presence of a single conformer of the dimer is confirmed by IR-UV and UV-UV hole-burning spectroscopic techniques. RIDIR (Resonant ion dip infrared) spectrum of the dimer shows a red-shift of 265 cm(-1) in the N-H stretching frequency with respect to that of the 7-azaindole monomer. Two planar double hydrogen bonded cyclic structures of the dimer have been predicted from DFT calculations. Comparison of experimental and theoretical N-H stretching frequencies confirms that the observed dimer is stabilized by N-H···N and C-H···N hydrogen bonding interactions. The less stable conformer with N-H···F and C-H···N interactions are not observed in the experiment. The competition between N-H···N and N-H···F interactions in the two dimeric structures are discussed from natural bond orbital (NBO) analysis. The current results demonstrate that fluorine makes a hydrogen bond of intermediate strength through cooperative interaction of another hydrogen bond (C-H···N) present in the dimer, although fluorine is believed to be very weak hydrogen bond acceptor.

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Structure and hydrogen bond vibrations of the jet-cooled 1:1 complex between 7-azaindole and formamide: A laser-induced fluorescence spectroscopy study

Cited by 7 publications

References 30 publications

Solvent Dependence of 7-Azaindole Dimerization

Solvent Dependence of 7-Azaindole Dimerization

Excited State Tautomerization of 7-Azaindole in a 1:1 Complex with δ-Valerolactam: A Comparative Study with the Homodimer

Structure of 7-Azaindole···2-Fluoropyridine Dimer in a Supersonic Jet: Competition between N–H···N and N–H···F Interactions

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