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Singlet Exciton Fission and Associated Enthalpy Changes with a Covalently Linked Bichromophore Comprising TIPS-Pentacenes Held in an Open Conformation

Lookup NU author(s): Dr Joshua Karlsson, Dr Alparsan Atahan, Emeritus Professor Anthony Harriman

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Abstract

© 2020 American Chemical Society. All rights reserved.A covalently linked bichromophore, embracing 6,13-bis(triisopropylsilylethinyl)pentacene (TIPS-pentacene) terminals bridged by a rigid fluorene spacer, generates a relatively high yield (i.e., 65 ± 6%) of the spin-correlated, triplet biexciton upon illumination in toluene. Under the same conditions, the extent of fluorescence quenching relative to the parent TIPS-pentacene approaches 97% and is insensitive to temperature. The biexciton, having overall singlet spin multiplicity, undergoes internal conversion in competition to spin decorrelation. These latter processes occur on the relatively slow time scale of a hundred or so nanoseconds, possibly reflecting the restricted level of electronic communication between the terminals. Spin decorrelation leads to evolution of an independent triplet pair with an overall quantum yield of 0.50 ± 0.06 and a lifetime of 8 ± 2 μs in deaerated toluene. Photoacoustic calorimetry (PAC) indicates three separate enthalpy changes: a very fast step associated with intramolecular singlet exciton fission to form the correlated triplet biexciton, a fast step essentially reflecting spin decorrelation, and a slow step associated with relaxation of the independent triplet pair. Analysis of the PAC data, in conjunction with the transient absorption results, establishes excitation energies for both spin-correlated and independent triplet pairs. Polar solvent enhances both fluorescence quenching and triplet formation at the expense of radiationless decay while temperature effects have been recorded for all important intermediate species.


Publication metadata

Author(s): Karlsson JKG, Atahan A, Harriman A, Tkachenko NV, Ward AD, Schaberle FA, Serpa C, Arnaut LG

Publication type: Article

Publication status: Published

Journal: Journal of Physical Chemistry A

Year: 2021

Volume: 125

Issue: 5

Pages: 1184–1197

Print publication date: 11/02/2021

Online publication date: 02/02/2021

Acceptance date: 02/04/2018

ISSN (print): 1089-5639

ISSN (electronic): 1520-5215

Publisher: American Chemical Society

URL: https://doi.org/10.1021/acs.jpca.0c09961

DOI: 10.1021/acs.jpca.0c09961


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