Secondment to the University of Tuebingen


Wassie Mersha Takele participated in the secondment at the Institute of Physical and Theoretical Chemistry at the University of Tuebingen, Germany. The main objective of his project was to investigate and influence the optical, spectral, and tautomerization properties of single molecules inside an optical microcavity. To achieve these objectives, various λ/2-microcavities were first prepared and characterized using a confocal microscope equipped with a spectrograph with a CCD camera. The bottom cavity mirror was prepared by sequentially evaporating 0.5 nm Cr, 30 nm Ag, and 70 nm SiO2 layers on a clean microscope coverslip, while the top cavity mirror was prepared on a convex lens by covering it with 0.5 nm Cr, 60 nm Ag, and 70 nm SiO2 layers, consecutively. Wassie then investigated the influence of the confined optical field of the microcavity on photophysical and the tautomerization properties of molecules at room temperature, by placing single phthalocyanine molecules inside the cavity. All single-molecule imaging, time trace, photon antibunching, and lifetime measurements were performed using a home-built laser scanning confocal microscope coupled with a time-correlation single-photon counting module (HydraHarp 400).

Interestingly, decreasing the lifetime of the singlet excited state by confined field of the microcavity significantly reduces transitions of individual molecules to the non-fluorescent triplet state, consequently slowing down of tautomerization reaction of PcS4 molecules were observed. Furthermore, results suggest that the weak coupling between a cavity mode and a molecular transition can be used to control the damaging of an excited molecule by reactive oxygen and to steer excited state photoinduced chemical processes towards the desired direction.


1 Mar., 2019 - 31 Aug., 2020


Tuebingen, Germany


Wassie Mersha Takele

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 711859.