TY - JOUR
T1 - Electron spin resonance of difluorobiphenyls in the phosphorescent triplet states. s-cis and s-trans conformers and fluorine hyperfine structure
AU - Tanigaki, Katsumi
AU - Yagi, Mikio
AU - Higuchi, Jiro
N1 - Funding Information:
This work was supported by a Grant-in-Aid for Scientific Research (6143002) from the Ministry of Education, Science and Culture. K.T. thanks NEC Corporation for a leave of absence during the term of this research.
Funding Information:
The geometry of biphenyl (BP) is governed by the delicate balance between the electronic conjugation of the two phenyl rings and the repulsion of the two ortho hydrogen atoms ( 1). In the ground state (G state), BP is known to be twisted by an angle of 42” in vapor phase (2), while it is planar in crystal form (3, 4). The phosphorescent triplet state ( T, state) of BP was confirmed to be planar by T + G absorption and photochemical quenching data (5)) and by precise phosphorescence analysis (6). The planarity of BP in the T1 state is also supported by ESR measurements in durene single crystals ( 7) and by theoretical calculations ( 8-10). This suggests that the central C-C bond connecting the two phenyl rings of biphenyl derivatives should have an “ethylenic” double-bond character, although it has a single-bond character in the G state. Therefore, s-cis and s-trans conformers should be observed for 2,2’-and 3,3’-disubstituted biphenyls in the T, states owing to the increased overlap population between the two central carbon atoms. Actually such conformers were detected for 2,2’-and 3,3’-dimethylbiphenyls with some ambiguities by Scheve and Wagner (11) but reasonably assigned by us for a related compound of 2,2-bipyridine (12-16).
PY - 1989/9
Y1 - 1989/9
N2 - Electron spin resonance spectra of 2,2′-, 3,3′-, and 4,4′-difluorobiphenyls (2DFBP, 3DFBP, and 4DFBP, respectively) in their phosphorescent triplet states have been studied in various matrices at 77 K. Two sets of peaks corresponding to the s-cis and s-trans conformers are observed for 2DFBP and 3DFBP. By using a stretched poly(vinyl alcohol) film as a host, the observed individual peaks are assigned. The 19F hyperfine splitting is obtained for 2DFBP and 4DFBP with a microwave magnetic field parallel to an external magnetic field (B ∥ Brf), which is different from the conventional resonance condition of B ⊥ Brf.
AB - Electron spin resonance spectra of 2,2′-, 3,3′-, and 4,4′-difluorobiphenyls (2DFBP, 3DFBP, and 4DFBP, respectively) in their phosphorescent triplet states have been studied in various matrices at 77 K. Two sets of peaks corresponding to the s-cis and s-trans conformers are observed for 2DFBP and 3DFBP. By using a stretched poly(vinyl alcohol) film as a host, the observed individual peaks are assigned. The 19F hyperfine splitting is obtained for 2DFBP and 4DFBP with a microwave magnetic field parallel to an external magnetic field (B ∥ Brf), which is different from the conventional resonance condition of B ⊥ Brf.
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U2 - 10.1016/0022-2364(89)90372-7
DO - 10.1016/0022-2364(89)90372-7
M3 - Article
AN - SCOPUS:0011624244
VL - 84
SP - 282
EP - 295
JO - Journal of Magnetic Resonance (1969)
JF - Journal of Magnetic Resonance (1969)
SN - 0022-2364
IS - 2
ER -