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Crystal structure, spectroscopic, and theoretical investigations of excited-state proton transfer in the doubly hydrogen-bonded dimer of 2-butylamino-6-methyl-4-nitropyridine N-oxide.
J Phys Chem A. 2006 Sep 21; 110(37):10690-8.JP

Abstract

The crystal structure of 2-butylamino-6-methyl-4-nitropyridine N-oxide (2B6M) was resolved on the basis of X-ray diffraction. Solid 2B6M occurs in the form of a doubly hydrogen-bonded dimer with squarelike hydrogen-bonding network composed of two intra- (2.556(2) A) and two intermolecular (2.891(2) A) N-H...O type hydrogen bonds. The molecule thus has both a protonable and a deprotonable group that led us to investigate the possibility of an excited-state proton transfer (ESIPT) reaction in different solvents by means of experimental absorption, steady state, and time-resolved emission spectroscopy. The results were correlated with quantum mechanical TD-DFT and PM3 calculations. Experimental and theoretical findings show the possibility of an ESIPT reaction in polar solvents. It is demonstrated that in particular the emission spectra of 2B6M are very sensitive to solvent properties, and a large value of the Stokes shift (about 8000 cm(-1)) in acetonitrile is indicative for an ESIPT process. This conclusion is further supported by time-resolved fluorescence decay measurents that show dual exponential decay in polar solvents. Vertical excitation energies calculated by TD-DFT reproduce the experimental absorption maxima in nonpolar solvents well. The majority of electronic transitions in 2B6M is of pi --> pi* character with a charge shift from the electron-donating to the electron-accepting groups. The calculations show that, due to the charge redistribution on excitation, the acidity of the amino group increases significantly, which facilitates the proton transfer from the amino to the N-oxide group in the excited state.

Authors+Show Affiliations

Faculty of Chemistry, University of Wrocław, ul. Joliot-Curie 14, 50-383 Wrocław, Poland. anias@wchuwr.chem.uni.wroc.plNo affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

16970358

Citation

Szemik-Hojniak, Anna, et al. "Crystal Structure, Spectroscopic, and Theoretical Investigations of Excited-state Proton Transfer in the Doubly Hydrogen-bonded Dimer of 2-butylamino-6-methyl-4-nitropyridine N-oxide." The Journal of Physical Chemistry. A, vol. 110, no. 37, 2006, pp. 10690-8.
Szemik-Hojniak A, Deperasiñska I, Jerzykiewicz L, et al. Crystal structure, spectroscopic, and theoretical investigations of excited-state proton transfer in the doubly hydrogen-bonded dimer of 2-butylamino-6-methyl-4-nitropyridine N-oxide. J Phys Chem A. 2006;110(37):10690-8.
Szemik-Hojniak, A., Deperasiñska, I., Jerzykiewicz, L., Sobota, P., Hojniak, M., Puszko, A., Haraszkiewicz, N., van der Zwan, G., & Jacques, P. (2006). Crystal structure, spectroscopic, and theoretical investigations of excited-state proton transfer in the doubly hydrogen-bonded dimer of 2-butylamino-6-methyl-4-nitropyridine N-oxide. The Journal of Physical Chemistry. A, 110(37), 10690-8.
Szemik-Hojniak A, et al. Crystal Structure, Spectroscopic, and Theoretical Investigations of Excited-state Proton Transfer in the Doubly Hydrogen-bonded Dimer of 2-butylamino-6-methyl-4-nitropyridine N-oxide. J Phys Chem A. 2006 Sep 21;110(37):10690-8. PubMed PMID: 16970358.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Crystal structure, spectroscopic, and theoretical investigations of excited-state proton transfer in the doubly hydrogen-bonded dimer of 2-butylamino-6-methyl-4-nitropyridine N-oxide. AU - Szemik-Hojniak,Anna, AU - Deperasiñska,Irena, AU - Jerzykiewicz,Lucjan, AU - Sobota,Piotr, AU - Hojniak,Marek, AU - Puszko,Aniela, AU - Haraszkiewicz,Natalia, AU - van der Zwan,Gert, AU - Jacques,Patrice, PY - 2006/9/15/pubmed PY - 2007/9/7/medline PY - 2006/9/15/entrez SP - 10690 EP - 8 JF - The journal of physical chemistry. A JO - J Phys Chem A VL - 110 IS - 37 N2 - The crystal structure of 2-butylamino-6-methyl-4-nitropyridine N-oxide (2B6M) was resolved on the basis of X-ray diffraction. Solid 2B6M occurs in the form of a doubly hydrogen-bonded dimer with squarelike hydrogen-bonding network composed of two intra- (2.556(2) A) and two intermolecular (2.891(2) A) N-H...O type hydrogen bonds. The molecule thus has both a protonable and a deprotonable group that led us to investigate the possibility of an excited-state proton transfer (ESIPT) reaction in different solvents by means of experimental absorption, steady state, and time-resolved emission spectroscopy. The results were correlated with quantum mechanical TD-DFT and PM3 calculations. Experimental and theoretical findings show the possibility of an ESIPT reaction in polar solvents. It is demonstrated that in particular the emission spectra of 2B6M are very sensitive to solvent properties, and a large value of the Stokes shift (about 8000 cm(-1)) in acetonitrile is indicative for an ESIPT process. This conclusion is further supported by time-resolved fluorescence decay measurents that show dual exponential decay in polar solvents. Vertical excitation energies calculated by TD-DFT reproduce the experimental absorption maxima in nonpolar solvents well. The majority of electronic transitions in 2B6M is of pi --> pi* character with a charge shift from the electron-donating to the electron-accepting groups. The calculations show that, due to the charge redistribution on excitation, the acidity of the amino group increases significantly, which facilitates the proton transfer from the amino to the N-oxide group in the excited state. SN - 1089-5639 UR - https://www.unboundmedicine.com/medline/citation/16970358/Crystal_structure_spectroscopic_and_theoretical_investigations_of_excited_state_proton_transfer_in_the_doubly_hydrogen_bonded_dimer_of_2_butylamino_6_methyl_4_nitropyridine_N_oxide_ L2 - https://doi.org/10.1021/jp062405x DB - PRIME DP - Unbound Medicine ER -