Wednesday, 12 February 2025 11:00am – 12:00pm

This seminar will be delivered in Chemistry Lecture Theatre 4

Speaker: Professor Jürgen Köhler

Host: Prof. Girish Lakhwani

Title: Towards photonic logic gates: Reversible, read-write-erase cycling using photoswitchable beads in micropatterned arrays

Abstract: Using surface-templated electrophoretic deposition, we have created arrays of polymer beads (photonic units) incorporating photo-switchable DAE molecules, which can be reversibly and individually switched between high and low emission states by direct photo-excitation, without any energy or electron transfer processes within the molecular system. The micropatterned array of these photonic units is spectroscopically characterized in detail and optimized with respect to both signal contrast and cross-talk. The optimum optical parameters including laser intensity, wavelength and duration of irradiation are elucidated and ideal conditions for creating reversible on/off cycles in a micropatterned array are determined. 500 such cycles are demonstrated with no obvious on/off contrast attenuation. The ability to process binary information is demonstrated by selectively writing information to the given photonic unit, reading the resultant emissive signal pattern and finally erasing the information again, which in turn demonstrates the possibility of continuous recording. This basic study paves the way for building complex circuits using spatially well-arranged photonic units.

Zhang, P. Dharpure, M. Philipp, P. Mulvaney, M. Thelakkat, J. Köhler Adv. Optical Mater. 12 (2024) 2401029

Bio: Jürgen Köhler has studied physics at the University of Düsseldorf (ph.D 1990) followed by a postdoc period at the University of Leiden (The Netherlands) untill 1999. After a stay at the LMU Munich as associate professor he became a full professor at the University of Bayreuth in 2000. In 2003 he denied an offer to move to the University of Linz (Austria).

His research interests cover the study of the electronic states of soft condensed matter, including (bio-)macromolecules and molecular aggregates, using optical (single-molecule) spectroscopy.

From 2000 – 2007 he has served as a member of the Scientific-Technical-Advisory Board of the Bavarian State Government. He was the initiator and chairman of the international conference “Light-Harvesting Processes” which took place biannually from 2007 – 2017. From 2010 – 2019 he was the spokesman of the Research Training Group “Photophysics of

Synthetic and Biological Multichromophoric Systems” at the University of Bayreuth. Currently Köhler serves as the Executive Director of the ‘Bayreuth Institute of Macromolecular Research’.

For his research he received several awards among which the Gustav-Hertz-Prize of the German Physical Society and a Wilsmore Fellowship from the University of Melbourne.