期刊
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
卷 116, 期 17, 页码 8178-8183出版社
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1820932116
关键词
singlet fission; electron paramagnetic resonance; spin state
资金
- Chemical Sciences, Geosciences, and Biosciences Division, Office of Basic Energy Sciences, Department of Energy [DE-FG02-99ER14999]
- Ryan Fellowship
- Northwestern University International Institute for Nanotechnology
- National Science Foundation Graduate Research Fellowship Program [DGE-1324585]
Singlet fission (SF) is a photophysical process in which one of two adjacent organic molecules absorbs a single photon, resulting in rapid formation of a correlated triplet pair (T1T1) state whose spin dynamics influence the successful generation of uncorrelated triplets (T-1). Femtosecond transient visible and near-infrared absorption spectroscopy of a linear terrylene-3,4:11,12-bis(dicarboximide) dimer (TDI2), in which the two TDI molecules are directly linked at one of their imide positions, reveals ultrafast formation of the (T1T1) state. The spin dynamics of the (T1T1) state and the processes leading to uncoupled triplets (T-1) were studied at room temperature for TDI2 aligned in 4-cyano-4'-pentylbiphenyl (5CB), a nematic liquid crystal. Time-resolved electron paramagnetic resonance spectroscopy shows that the (T1T1) state has mixed (5)(T1T1) character at room temperature. This mixing is magnetic field dependent, resulting in a maximum triplet yield at similar to 200 mT. The accessibility of the (3)(T1T1) state opens a pathway for triplet-triplet annihilation that produces a single uncorrelated T-1 state. The presence of the (5)(T1T1) state at room temperature and its relationship with the (1)(T1T1) and (3)(T1T1) states emphasize that understanding the relationship among different (T1T1) spin states is critical for ensuring high-yield T-1 formation from singlet fission.
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