Infrared-optical double resonance spectroscopic measurements on 2-(2'-pyridyl)benzimidazole and its hydrogen bonded complexes with water and methanol.
The H(2)O and MeOH complexes of 2-(2'-pyridyl)benzimidazole (2PBI) were investigated using laser induced fluorescence and IR-UV double resonance spectroscopic techniques. The 0(0)(0) band for the S(1) <-- S(0) electronic transition of 2PBI was observed at 31,616 cm(-1), and corresponding transitions for the H(2)O and MeOH complexes show substantial red shifts of 1059 and 1203 cm(-1), respectively. A long progression up to v' = 5 in the 92 cm(-1) vibrational mode was observed for bare 2PBI, which is considerably shortened to v' = 2 and v' = 1 for the H(2)O and MeOH complexes, respectively. The combined experimental and theoretical results suggest that both H(2)O and MeOH form cyclic complex with 2PBI incorporating N-H...O and O-H...N hydrogen bonds. Comparison with other known hydrogen-bonded H(2)O complexes of bifunctional aza-heteroaromatic molecules suggest that 2PBI-H(2)O is probably one of the strongest of all known complexes. Further, the experimental data in combination with calculations suggests that the hydrogen atom/proton transfer leading to tautomeric form might be thermodynamically spontaneous in the electronic excited state, due to explicit solvent (H(2)O and MeOH) participation.
Guin
Mridula
M
Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India.
Maity
Surajit
S
Patwari
G Naresh
GN
D001562:Benzimidazoles / Q000737:chemistry*; D006860:Hydrogen Bonding; D000432:Methanol / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D011522:Protons; D013055:Spectrophotometry, Infrared / Q000379:methods*; D014867:Water / Q000737:chemistry*
C479869:2-(2'-pyridyl)benzimidazole; D001562:Benzimidazoles; D011522:Protons; D014867:Water; D000432:Methanol