Photophysics of azobenzene constrained in a UiO metal-organic framework: effects of pressure, solvation and dynamic disorder

Sussardi, A., Marshall, R. J., Moggach, S. A., Jones, A. C. and Forgan, R. S. (2021) Photophysics of azobenzene constrained in a UiO metal-organic framework: effects of pressure, solvation and dynamic disorder. Chemistry: A European Journal, 27(60), pp. 14871-14875. (doi: 10.1002/chem.202101879) (PMID:34468054)

Abstract

Photophysical studies of chromophoric linkers in metal-organic frameworks (MOFs) are undertaken commonly in the context of sensing applications, in search of readily observable changes of optical properties in response to external stimuli. The advantages of the MOF construct as a platform for investigating fundamental photophysical behaviour have been somewhat overlooked. The linker framework offers a unique environment in which the chromophore is geometrically constrained and its structure can be determined crystallographically, but it exists in spatial isolation, unperturbed by inter-chromophore interactions. Furthermore, high-pressure studies enable the photophysical consequences of controlled, incremental changes in local environment or conformation to be observed and correlated with structural data. We demonstrate this approach in the present study of the trans -azobenzene chromophore, constrained in the form of the 4’4-azobenzenedicarboxylate (abdc) linker, in a UiO topology framework. We report previously unobserved effects of pressure-induced solvation and conformational distortion on the lowest energy, np* transition, and interpret these in the light of crystallographic data. We find that trans -azobenzene remains non-fluorescent (with a quantum yield less than 10 -4 ) despite the prevention of trans-cis isomerization by the constraining MOF structure. We propose that efficient non-radiative decay is mediated by the local, pedal-like twisting of the azo group that is evident as dynamic disorder in the crystal structure.

• Item Type: Articles
• Additional Information: We would like to acknowledge the LPDP Indonesia Endowment Fund for Education for a PhD Scholarship to AS. RSF and RJM thank EPSRC for funding (EP/L004461/1). SAM thanks the Australian Research Council (ARC) for a Future Fellowship (FT200100243).
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Forgan, Professor Ross and MARSHALL, Ross James
• Authors: Sussardi, A., Marshall, R. J., Moggach, S. A., Jones, A. C., and Forgan, R. S.
• College/School: College of Science and Engineering > School of Chemistry
• Journal Name: Chemistry: A European Journal
• Publisher: Wiley
• ISSN: 0947-6539
• ISSN (Online): 1521-3765
• Published Online: 01 September 2021
• Copyright Holders: Copyright © 2021 The Authors
• First Published: First published in Chemistry: A European Journal 27(60): 14871-14875
• Publisher Policy: Reproduced under a Creative Commons License
• Data DOI: 10.5525/gla.researchdata.1181

Project Code	Award No	Project Name	Principal Investigator	Funder's Name	Funder Ref	Lead Dept
168273		Biomimetic guest selective metal-organic frameworks: catalysis and self-assembly	Ross Forgan	Engineering and Physical Sciences Research Council (EPSRC)	EP/L004461/1	Chemistry