Online Seminar Announcement: Wednesday 4 August 2021

Wednesday 4 August 2021

Time: 1pm in QLD, NSW, ACT, Vic, and Tas

11am in WA 12:30pm in NT

12:30pm in SA

3pm in New Zealand

Meeting URL: https://jcu.zoom.us/j/82093241646

Seminar schedule

Each talk is 20 minutes duration followed by approximately 5 minutes for questions and discussion.

Time (QLD time, adjust as needed)

Presentation
1:00 – 1:25pm

Anisotropic Triplet Exciton Diffusion in Crystalline TIPS-Pentacene

Rohan J. Hudson, D.M. Huang and T.W. Kee

The University of Adelaide, Adelaide, South Australia, Australia

Singlet fission (SF) is a spin-allowed exciton multiplication process in which coupling of an excited singlet-state (S1) chromophore to an adjacent ground-state chromophore yields two triplet-state (T1) excited chromophores. This process has the potential to circumvent the theoretical efficiency limit for single-function photovoltaics, and as such has attracted significant interest in recent years. Organic SF chromophores typically exhibit significant structural anisotropy in their crystal packing, which can impact exciton transport and influence the design of SF-enhanced devices. An improved understanding of the link between structural anisotropy and exciton diffusion is therefore crucial for developing SF-based photovoltaics.
Here we use ultrafast transient absorption spectroscopy to quantify the anisotropy in the triplet exciton mobility of crystalline 6,13-(triisopropylsilylethynyl)-pentacene (TIPS-Pn), a prototypical SF chromophore. Bimolecular triplet−triplet annihilation in crystalline TIPS-Pn is well-described by a kinetic model that assumes isotropic, three-dimensional triplet exciton diffusion, but with physically unreasonable best fit parameters. Kinetic models that assume either one-dimensional or anisotropic three-dimensional exciton diffusion describe the data equally well but yield more physically realistic fit parameters, suggesting that triplet diffusion on the sub-nanosecond time scale occurs mostly along a single axis of the material. Diffusion coefficients calculated by density functional theory predict that triplet exciton diffusion occurs predominantly along the crystallographic a-axis, with migration in any other direction slower by over an order of magnitude. These findings highlight the need to treat parameters obtained from fits of experimental data with models of isotropic diffusion with caution for systems with anisotropic packing such as TIPS-Pn, and suggest that fast, directional exciton transport in layers or films of TIPS-Pn may be achieved by control of the chromophore morphology.

 

1:25 – 1:50pm

Structure-Property Relationships in Molecular Electronics

Masnun Naher,a Elena Gorenskaia,a Wenjing Hong,b Colin J. Lambert,c Richard J. Nichols,d Paul J. Low a*

a University of Western Australia, Australia;

b Xiamen University, China;

c Lancaster University, UK;

d University of Liverpool, UK

Molecular electronics (ME) is a rapidly maturing field concerned with the study of charge transport phenomena through a single molecule or an array of molecules organized between two (or more) macroscopic electrodes (Figure 1). By the careful design of the chemical structure it’s possible to study the different charge transport mechanism such as coherent tunneling and incoherent hopping and quantum interference phenomenon within the junction to achieve the functions of conventional electronic components such as chemical sensors and chemically-gated transistors (Chem-FETs), photodetectors, and thermoelectric materials.1
This presentation will describe the design and synthesis of range of linearly and cross-conjugated organic, organometallic and coordination complexes complex to study their electronic properties in the molecular junction. At the heart of this study is the exploration of the factors that influence electron transport through a molecule. In turn, this deeper understanding allows us to extend molecular design strategies beyond the search for highly conductive molecules and direct attention to more subtle concepts such as quantum interference,2 redox-gated molecular electronic response1 and the influence of the molecule-electrode contact1 and coupling to the overall electrical response of the junction (Figure 1). Molecular parameters such as the frontier orbital energy levels and HOMO-LUMO gap of the molecular candidates in their accessible redox states are therefore essential to these investigations. Therefore, in addition to the molecular junction-based measurements of molecular conductivity, investigation of the electronic structures and electrochemical properties of these molecular candidates using electrochemical, spectroelectrochemical and computational methods has also been undertaken.3

 

Figure 1: A schematic of a single-molecule junction, showing the conceptual features of the anchor group contacting to the electrode surface, a linking group or molecular backbone and some functional unit (e.g. a metal-ligand fragment).

The performance of the synthesised compounds to understand different charge transport mechanisms is being evaluated within scanning tunneling microscope break-junction (STM-BJ) in collaboration with Liverpool University (UK), and the theoretical calculations of molecular structure and model junctions were done in collaboration with Lancaster University (UK) and Xiamen University (China), and results will be reported.

References
1. M. Naher, D. C. Milan, O. A. Al-Owaedi, I. J. Planje, S. Bock, J. Hurtado-Gallego, P. Bastante, Z. M. Abd Dawood, L. Rincón-García, G. Rubio-Bollinger, S. J. Higgins, N. Agraït, C. J. Lambert, R. J. Nichols and P. J. Low, J. Am. Chem. Soc., 2021, DOI: 10.1021/jacs.0c11605.
2. F. Jiang, D. I. Trupp, N. Algethami, H. Zheng, W. He, A. Alqorashi, C. Zhu, C. Tang, R. Li, J. Liu, H. Sadeghi, J. Shi, R. Davidson, M. Korb, A. N. Sobolev, M. Naher, S. Sangtarash, P. J. Low, W. Hong and C. J. Lambert, Angew. Chem. Int. Ed., 2019, 58, 18987-18993.
3. M. Naher, S. Bock, Z. M. Langtry, K. M. O’Malley, A. N. Sobolev, B. W. Skelton, M. Korb and P. J. Low, Organometallics, 2020, 39, 4667-4687.

1:50 – 2:00pm – Questions and discussion

During the seminar:

• Please keep your microphone muted unless you are speaking. This is to reduce the background noise and avoid disrupting the presenter.

• You will be automatically muted when you join the virtual meeting room. To speak, you will need to unmute yourself by using the audio controls in the lower left of the Zoom window.

• If you have not used Zoom before, then it is recommended that you join 5 minutes before the starting time to ensure that you have your software set up correctly.

Please be aware that the talks will be recorded and posted on the AUCAOS website.

Previous seminars:

Previous seminars can be viewed here: https://seminars.aucaos.org.au/

Call for abstracts:

Seminars are typically held on the first Wednesday of each month.

At this time we are specifically encouraging HDR students to present their work to broad audience. If you are interested in speaking then please submit an abstract to bronson.philippa@jcu.edu.au.