Theoretical Prediction of Isotope Effects on Charge Transport in Organic Semiconductors.
We suggest that the nuclear tunneling effect is important in organic semiconductors, which we showed is absent in both the widely employed Marcus theory and the band-like transport as described by the deformation potential theory. Because the quantum nuclear tunneling tends to favor electron transfer while heavier nuclei decrease the quantum effect, there should occur an isotope effect for carrier mobility. For N,N'-n-bis(n-hexyl)-naphthalene diimide, electron mobility of all-deuteration on alkyls and all (13)C-substitution on the backbone decrease ∼18 and 7%, respectively. Similar isotope effects are found in the N,N'-n-bis(n-octyl)-perylene diimide. However, there is nearly no isotope effect for all-deuterated rubrene or tetracene. We have found that the isotopic effect only occurs when the substituted nuclei contribute actively to vibrations with appreciable charge reorganization energy and coupling with carrier motion. Thus, this prediction can shed light on the current dispute over the hopping versus band-like mechanisms in organic semiconductors.
†MOE Key Laboratory of Organic OptoElectronics and Molecular Engineering, Department of Chemistry, Tsinghua University, Beijing 100084, People's Republic of China.
Yuqian
Y
Jiang
‡Key Laboratory of Organic Solids, Beijing National Laboratory for Molecular Sciences (BNLMS), Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, People's Republic of China.
Hua
H
Geng
†MOE Key Laboratory of Organic OptoElectronics and Molecular Engineering, Department of Chemistry, Tsinghua University, Beijing 100084, People's Republic of China.
Wen
W
Shi
‡Key Laboratory of Organic Solids, Beijing National Laboratory for Molecular Sciences (BNLMS), Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, People's Republic of China.
Qian
Q
Peng
†MOE Key Laboratory of Organic OptoElectronics and Molecular Engineering, Department of Chemistry, Tsinghua University, Beijing 100084, People's Republic of China.
Xiaoyan
X
Zheng
†MOE Key Laboratory of Organic OptoElectronics and Molecular Engineering, Department of Chemistry, Tsinghua University, Beijing 100084, People's Republic of China.
Zhigang
Z
Shuai
charge mobility; isotope effects; naphthalene diimide; nuclear tunneling; organic semiconductors; perylene diimide