Poster Award for Dr. Pavel Malý (AK Brixner)

The 13^th International Conference on Optical Probes of Organic and Hybrid Optoelectronic Materials and Applications 2019 is the premier international meeting bringing together scientists and engineers from around the world interested in the field of photophysics of organic and hybrid semiconductors. Prof. Brixner (Invited Speaker) and some of his co-workers attended the conference in Lithuania.

The poster presentation of Dr. Pavel Malý, entitled "Exciton dynamics and interaction in squariane copolymers of varying length, probed by 5th order two-dimensional electronic spectroscopy", was awarded with the Best Poster Presentation Award - a cooperation between Pavel Malý, Julian Lüttig, Arthur Turkin, Jakub Dostál, Christoph Lambert and Tobias Brixner.

In the presented work they used exciton-exciton interaction two-dimensional electronic spectroscopy (EEI2D) to observe exciton dynamics and exciton-exciton annihilation in squaraine copolymers. Exciton dynamics in conjugated systems is a key process for both for natural (photosynthesis) and artificial (organic photovoltaics) light harvesting. After photoexcitation, the excitons are delocalized and move in a wavelike fashion. Over propagation time and distance this dynamics changes into a diffusive motion. To observe this transition is challenging, as one needs to resolve both the initial dynamics (which is ultrafast) and the long-range diffusion (which has no spectral signature in the absence of energy gradient). In the EEI2D approach they utilize pairs of excitons, interacting by exciton-exciton annihilation, to observe the exciton motion in polymers of controlled length. While in short polymers the confined excitons interact practically immediately, in long polymers the exciton diffusion gains significance. The key finding is that, due to the polymer disorder, the excitons are trapped in local energetic minima and move through the polymer in a sub-diffusive way. This behavior determines the polymer energy transport properties, such as the exciton diffusion speed and length.

Website of Prof. Brixner