Stacking effect of polyfluorene on the chemical shift and electron transport.
We investigate the structures, NMR chemical shifts, absorption spectra, frontier molecular orbitals, and transition density matrices of pi-stacked polyfluorenes by ab initio calculations. For F1-F4, we consider two different conformations, syn and anti. The simulated 1H NMR chemical shifts are in good agreement with the previous experiment, and the significantly upfielded chemical shifts explain that the fluorene moieties are stacked on each other. It is found that the relative stability for syn and anti conformers is almost equivalent in B3LYP calculations; however, the syn conformer becomes much more stable than the anti conformer in MP2 calculations, which is consistent with the experimental finding that only the syn conformers are relevant. The vertical detachment energy, which is linearly proportional to the ionization potential, shows the same size dependence as the previous experiment. The electron attachment energy decreases exponentially as the size increases, which implies that the electron transport would be possible even for long chains such as F3 and F4. This was evident from the frontier molecular orbitals (HOMO and LUMO). Also, it is found that the syn conformers are very favorable for electron transport through the pi-stacked fluorene moieties.
Kim
Woo Seong
WS
Department of Chemistry, Chonnam National University, 300 Yongbong-Dong, Bugku, Gwangju, 500-757, Korea.
Kim
Jongseob
J
Park
Jong Keun
JK
Mukamel
Shaul
S
Rhee
Soon Ki
SK
Choi
Yong Kook
YK
Lee
Jin Yong
JY
D001703:Biophysics / Q000379:methods; D002627:Chemistry, Physical / Q000379:methods; D004579:Electron Transport; D004583:Electrons; D005449:Fluorenes / Q000737:chemistry*; D007477:Ions; D009682:Magnetic Resonance Spectroscopy; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation; D011108:Polymers / Q000737:chemistry / Q000494:pharmacology*; D011522:Protons; D013053:Spectrophotometry / Q000379:methods; D013055:Spectrophotometry, Infrared; D013059:Spectrum Analysis, Raman
D005449:Fluorenes; D007477:Ions; D011108:Polymers; D011522:Protons