Impact of molecular structure on singlet and triplet exciton diffusion in phenanthroline derivatives

Deepesh Rai, John S. Bangsund, Javier Garcia Barriocanal, Russell J. Holmes

Research output: Contribution to journalArticlepeer-review

7 Scopus citations


We demonstrate the impact of subtle changes in molecular structure on the singlet and triplet exciton diffusion lengths (LD) for derivatives of the archetypical electron-transport material 4,7-diphenyl-1,10-phenanthroline (BPhen). Specifically, this work offers a systematic characterization of singlet and triplet exciton transport in identically prepared thin films, highlighting the differing dependence on molecular photophysics and intermolecular spacing. For luminescent singlet excitons, photoluminescence quenching measurements yield an LD from <1 nm for BPhen, increasing to (5.4 ± 1.2) nm for 2,9-dichloro-4,7-diphenyl-1,10-phenanthroline (BPhen-Cl2) and (3.9 ± 1.1) nm for 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP). The diffusion of dark triplet excitons is probed using a phosphorescent sensitizer-based method where triplets are selectively injected into the material of interest, with those migrating through the material detected via energy transfer to an adjacent, phosphorescent sensitizer. Interestingly, the triplet exciton LD decreases from (15.4 ± 0.4) nm for BPhen to (8.0 ± 0.7) nm for BPhen-Cl2 and (4.0 ± 0.5) nm for BCP. The stark difference in behavior observed for singlets and triplets with functionalization is explicitly understood using long-range Förster and short-range Dexter energy transfer mechanisms, respectively.

Original languageEnglish (US)
Pages (from-to)6118-6123
Number of pages6
JournalJournal of Materials Chemistry C
Issue number18
StatePublished - May 14 2020

Bibliographical note

Funding Information:
This work was supported by National Science Foundation (NSF) Solid-State and Materials Chemistry under DMR-1708177 and Electronics, Photonics and Magnetic Devices under ECCS-1509121. J. S. B. acknowledges support from the NSF Graduate Research Fellowship under Grant No 00039202. R. J. H. would like to acknowledge support from a Leverhulme Trust Visiting Professorship at the University of Cambridge and a Visiting Fellowship at Clare Hall, University of Cambridge. The authors acknowledge C. P. Clark for X-ray diffraction measurements and Dr A. Healy for measuring singlet exciton lifetimes using TCSPC.

Publisher Copyright:
© 2020 The Royal Society of Chemistry.


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