Single conformation spectroscopy of a flexible bichromophore: 3-(4-hydroxyphenyl)-N-benzylpropionamide.
Resonant two-photon ionization (R2PI), UV hole-burning (UVHB), and resonant ion-dip infrared (RIDIR) spectroscopy have been used to study the single-conformation infrared and ultraviolet spectroscopy of 3-(4-hydroxyphenyl)-N-benzylpropionamide (HNBPA, HOC6H5CH2CH2(CO)NHCH2C6H5) cooled in a supersonic expansion. UVHB determines the presence of three conformers, two of which dominate the spectrum. RIDIR spectra in the OH stretch (3600-3700 cm(-1)), amide NH stretch (3450-3500 cm(-1)), and CO stretch (1700-1750 cm(-1)) regions reveal the presence of small shifts in these fundamentals that are characteristic of the folding of the flexible chain and the ring-ring and ring-chain interactions. On the basis of a comparison of the experimental frequency shifts with calculations, the two major experimentally observed conformers are assigned to two folded structures in which the two aromatic rings are (nominally) face-to-face and perpendicular to one another. The perpendicular structure has a transition assignable to the S0-S2 origin, while the face-to-face structure does not, consistent with a faster nonradiative process in the latter case. The calculated structures and vibrational frequencies are quite sensitive to the level of theory due to the flexibility of the interconnecting chain and the importance of dispersive interactions between the two aromatic rings.
Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907-2084, USA.
Esteban E
EE
Baquero
William H
WH
James
Tae Hoon
TH
Choi
Kenneth D
KD
Jordan
Timothy S
TS
Zwier
D000577:Amides / Q000737:chemistry*; D001593:Benzyl Compounds / Q000737:chemistry*; D004396:Coloring Agents / Q000737:chemistry*; D003198:Computer Simulation; D008956:Models, Chemical; D008968:Molecular Conformation; D015394:Molecular Structure; D013055:Spectrophotometry, Infrared; D013056:Spectrophotometry, Ultraviolet; D013816:Thermodynamics
C533911:3-(4-hydroxyphenyl)-N-benzylpropionamide; D000577:Amides; D001593:Benzyl Compounds; D004396:Coloring Agents