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Title: Dynamic broadening alters triplet extinction coefficients in fluorene oligomers and polymers

Abstract

We report T n ← T 1 spectra and extinction coefficients, ε, and other properties as functions of chain length for a series of fluorene oligomers, oF n, and polymers, pF n, with n = 2–84 repeat units. We find that ε increases with length, peaking at 159 400 M –1 cm –1 for oF 3 and then decreases for longer chains. ε does not scale with 1/n or e–n to reach a constant value at long length, as predicted by the commonly applied oligomer extrapolation approximation, although spectral shifts, oscillator strengths, and transition dipole moments do reach limiting values for chains near 10 units long. While computations describe the triplet in oF 2 and oF 3 as having similar geometries with a single flattened dihedral angle between units, computations and simulations suggest that in longer oligomers motion along the chains of the short 2–3 unit, the long T 1 state is probably the source of the unusual changes in ε. Furthermore, these occur because hopping along the chain is sufficiently fast that the dihedrals between fluorene units cannot fully relax. At a length near 10 units, hopping and dihedral angle changes produce a steady state distribution of geometries withmore » only small changes from the ground state, which persist for longer chains. Additional decreases in ε from pF 28 to pF 84 are plausibly due to a small number of chain defects which result in loss of triplets.« less

Authors:
ORCiD logo [1];  [1];  [2];  [3]; ORCiD logo [1]
  1. Brookhaven National Lab. (BNL), Upton, NY (United States)
  2. Sirindhorn International Inst. of Technology (SIIT), Bangkok (Thailand)
  3. Kyoto Inst. of Technology, Kyoto (Japan)
Publication Date:
Research Org.:
Brookhaven National Lab. (BNL), Upton, NY (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1583112
Alternate Identifier(s):
OSTI ID: 1581666
Report Number(s):
BNL-213532-2020-JAAM
Journal ID: ISSN 0021-9606
Grant/Contract Number:  
SC0012704
Resource Type:
Accepted Manuscript
Journal Name:
Journal of Chemical Physics
Additional Journal Information:
Journal Volume: 152; Journal Issue: 2; Journal ID: ISSN 0021-9606
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY

Citation Formats

Cook, Andrew R., Girimonti, Anthony, Sreearunothai, Paiboon, Asaoka, Sadayuki, and Miller, John R. Dynamic broadening alters triplet extinction coefficients in fluorene oligomers and polymers. United States: N. p., 2020. Web. doi:10.1063/1.5132798.
Cook, Andrew R., Girimonti, Anthony, Sreearunothai, Paiboon, Asaoka, Sadayuki, & Miller, John R. Dynamic broadening alters triplet extinction coefficients in fluorene oligomers and polymers. United States. doi:10.1063/1.5132798.
Cook, Andrew R., Girimonti, Anthony, Sreearunothai, Paiboon, Asaoka, Sadayuki, and Miller, John R. Wed . "Dynamic broadening alters triplet extinction coefficients in fluorene oligomers and polymers". United States. doi:10.1063/1.5132798.
@article{osti_1583112,
title = {Dynamic broadening alters triplet extinction coefficients in fluorene oligomers and polymers},
author = {Cook, Andrew R. and Girimonti, Anthony and Sreearunothai, Paiboon and Asaoka, Sadayuki and Miller, John R.},
abstractNote = {We report Tn ← T1 spectra and extinction coefficients, ε, and other properties as functions of chain length for a series of fluorene oligomers, oFn, and polymers, pFn, with n = 2–84 repeat units. We find that ε increases with length, peaking at 159 400 M–1 cm–1 for oF3 and then decreases for longer chains. ε does not scale with 1/n or e–n to reach a constant value at long length, as predicted by the commonly applied oligomer extrapolation approximation, although spectral shifts, oscillator strengths, and transition dipole moments do reach limiting values for chains near 10 units long. While computations describe the triplet in oF2 and oF3 as having similar geometries with a single flattened dihedral angle between units, computations and simulations suggest that in longer oligomers motion along the chains of the short 2–3 unit, the long T1 state is probably the source of the unusual changes in ε. Furthermore, these occur because hopping along the chain is sufficiently fast that the dihedrals between fluorene units cannot fully relax. At a length near 10 units, hopping and dihedral angle changes produce a steady state distribution of geometries with only small changes from the ground state, which persist for longer chains. Additional decreases in ε from pF28 to pF84 are plausibly due to a small number of chain defects which result in loss of triplets.},
doi = {10.1063/1.5132798},
journal = {Journal of Chemical Physics},
number = 2,
volume = 152,
place = {United States},
year = {2020},
month = {1}
}

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