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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 46: Focus Session: Ultrafast Processes in Organic Semiconductors and Perovskites II (joint session O/CPP)

CPP 46.9: Talk

Thursday, March 21, 2024, 17:15–17:30, MA 004

Structural Dynamics during Excimer Formation in Fluorinated Zinc-Phthalocyanine Thin Films — •Sebastian Hammer¹, Laurenz Kremeyer¹, Tristan Britt¹, Maximilian Rödel², Jens Pflaum^2,3, and Bradley Siwick¹ — ¹Departments for Physics and Chemistry, McGill University, Montreal, QC H3A 2K6, Canada — ²Experimental Physics VI, University of Würzburg, 97074 Würzburg — ³CAE (Center of Applied Energy Research) Bayern,, 97074 Würzburg

In molecular solids, the coupling of charge-transfer and Frenkel states facilitated by inter-molecular vibrational modes can lead to the formation of so called excimer states [1]. The formation of these energetically low lying states is accompanied by a significant structural deformation of the local inter-molecular geometry.

In this contribution we examine the dynamics of the structural deformation during the excimer formation in polycrystalline α-zinc-phthalocyanine thin films by means of ultrafast electron diffraction. Our findings show that the geometric relaxation follows a two-step process (300 fs and ≈15 ps) and the final geometry is stable beyond 300 ps. Tuning the inter-molecular interaction by means of molecular fluorination reveals that the time-scales of the structural relaxation process are critically dependent on the local energetic environment.

Funding from the DFG (Project 490894053) is gratefully acknowledged.

[1] Bialas et al. J. Chem. Phys. C. 126 4067-4081 (2022)

Keywords: excimer; structural dynamics; ultrafast electron diffraction; zinc-phthalocyanine