Triplet Exciton Management via Solid-State Interactions in Organic Semiconductors

Tightly-bound excitons play an important role in the function of molecular materials for light emission and light harvesting. This thesis investigates the effects of solid-state interactions on triplet excitons in a new family of organometallic light emitters, carbene-metal-amides (CMAs). Triplet excitons are normally silent in luminescence due to the spin-forbidden decay process, whereas effectively harvesting triplet excitons helps to boost the performance of light-emitting devices. As the triplet excitons are sensitive to both molecular properties and external environment, in this thesis we deploy optical spectroscopy techniques to understand the effect of solid-state interactions on triplet excitons. After introducing the relevant theoretical and experimental background of triplet formation in a single molecule and interactions between molecules, we firstly describe the intermolecular electrostatic interactions and the role of triplet diffusion and find that the combined effects of both blueshift the charge-transfer energy while other photophysical properties remain relatively constant in gold-bridged CMA1. We then describe the crystallisation of CMA1 thin films, which allows us to experimentally investigate the link between molecular conformations and photophysical properties. A combination of restricted torsional distortion and molecular electronic polarisation greatly blueshifts the charge-transfer emission by around 400 meV in the crystalline versus the amorphous phase. We also discover that the intersystem crossing rate and emission kinetics are unaffected by the extent of torsional distortion. Finally, we apply electrostatic interactions to the other two coinage metal-bridged CMAs to explore the effect of heavy metal atoms on the intersystem crossing and luminescence mechanism. We show that the photophysical properties do not reflect expected trends based upon the heavy atom effect as both direct coupling between charge-transfers states and spin-vibronic coupling via an intermediate state are present.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2020

Author dc:creator

• Feng, Jiale

Advisor dc:contributor.advisor

• Greenham, Neil

• photophysics
• optoelectronics
• organic semiconductors

Licence

• https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/305928e8-75eb-453c-a24f-7c08cf70380e/download
• https://www.rioxx.net/licenses/all-rights-reserved/

Language dc:language

eng

Author Identifier

0000-0002-4729-9404

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/311065