Substituent effects on energetics and crystal morphology modulate singlet fission in 9,10-bis(phenylethynyl)anthracenes

Youn Jue Bae, Joseph A. Christensen, Gyeongwon Kang, Jiawang Zhou, Ryan M. Young, Yi Lin Wu, Richard P. Van Duyne, George C. Schatz, Michael R Wasielewski

Research output: Contribution to journalArticle

Abstract

Singlet fission (SF) converts a singlet exciton into two triplet excitons in two or more electronically coupled organic chromophores, which may then be used to increase solar cell efficiency. Many known SF chromophores are unsuitable for device applications due to chemical instability or low triplet state energies. The results described here show that efficient SF occurs in derivatives of 9,10-bis(phenylethynyl)anthracene (BPEA), which is a highly robust and tunable chromophore. Fluoro and methoxy substituents at the 4- A nd 4′-positions of the BPEA phenyl groups control the intermolecular packing in the crystal structure, which alters the interchromophore electronic coupling, while also changing the SF energetics. The lowest excited singlet state (S1) energy of 4,4′-difluoro-BPEA is higher than that of BPEA so that the increased thermodynamic favorability of SF results in a (16 ± 2 ps)-1 SF rate and a 180% ± 16% triplet yield, which is about an order of magnitude faster than BPEA with a comparable triplet yield. By contrast, 4-fluoro-4′-methoxy-BPEA and 4,4′-dimethoxy-BPEA have slower SF rates, (90 ± 20 ps)-1 and (120 ± 10 ps)-1, and lower triplet yields, (110 ± 4)% and (168 ± 7)%, respectively, than 4,4′-difluoro-BPEA. These differences are attributed to changes in the crystal structure controlling interchromophore electronic coupling as well as SF energetics in these polycrystalline solids.

Original languageEnglish
Article number044501
JournalJournal of Chemical Physics
Volume151
Issue number4
DOIs
Publication statusPublished - Jul 28 2019

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crystal morphology
anthracene
fission
Crystals
Chromophores
chromophores
Crystal structure
excitons
crystal structure
9,10-bis(phenylethynyl)anthracene
Excited states
Electron energy levels
electronics
Solar cells
atomic energy levels
Thermodynamics
Derivatives
solar cells
thermodynamics
energy

ASJC Scopus subject areas

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry

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Substituent effects on energetics and crystal morphology modulate singlet fission in 9,10-bis(phenylethynyl)anthracenes. / Bae, Youn Jue; Christensen, Joseph A.; Kang, Gyeongwon; Zhou, Jiawang; Young, Ryan M.; Wu, Yi Lin; Van Duyne, Richard P.; Schatz, George C.; Wasielewski, Michael R.

In: Journal of Chemical Physics, Vol. 151, No. 4, 044501, 28.07.2019.

Research output: Contribution to journalArticle

Bae, Youn Jue ; Christensen, Joseph A. ; Kang, Gyeongwon ; Zhou, Jiawang ; Young, Ryan M. ; Wu, Yi Lin ; Van Duyne, Richard P. ; Schatz, George C. ; Wasielewski, Michael R. / Substituent effects on energetics and crystal morphology modulate singlet fission in 9,10-bis(phenylethynyl)anthracenes. In: Journal of Chemical Physics. 2019 ; Vol. 151, No. 4.
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AB - Singlet fission (SF) converts a singlet exciton into two triplet excitons in two or more electronically coupled organic chromophores, which may then be used to increase solar cell efficiency. Many known SF chromophores are unsuitable for device applications due to chemical instability or low triplet state energies. The results described here show that efficient SF occurs in derivatives of 9,10-bis(phenylethynyl)anthracene (BPEA), which is a highly robust and tunable chromophore. Fluoro and methoxy substituents at the 4- A nd 4′-positions of the BPEA phenyl groups control the intermolecular packing in the crystal structure, which alters the interchromophore electronic coupling, while also changing the SF energetics. The lowest excited singlet state (S1) energy of 4,4′-difluoro-BPEA is higher than that of BPEA so that the increased thermodynamic favorability of SF results in a (16 ± 2 ps)-1 SF rate and a 180% ± 16% triplet yield, which is about an order of magnitude faster than BPEA with a comparable triplet yield. By contrast, 4-fluoro-4′-methoxy-BPEA and 4,4′-dimethoxy-BPEA have slower SF rates, (90 ± 20 ps)-1 and (120 ± 10 ps)-1, and lower triplet yields, (110 ± 4)% and (168 ± 7)%, respectively, than 4,4′-difluoro-BPEA. These differences are attributed to changes in the crystal structure controlling interchromophore electronic coupling as well as SF energetics in these polycrystalline solids.

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