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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 28: Molecular Electronics and Excited State Properties (joint session CPP/TT)

CPP 28.9: Talk

Wednesday, March 29, 2023, 11:45–12:00, GÖR 226

Charge Delocalization and Vibronic Couplings in Quadrupolar Squaraine Dyes — Daniel Timmer¹, Fulu Zheng², Moritz Gittinger¹, Thomas Quenzel¹, •Daniel C. Lünemann¹, Katrin Winte¹, Yu Zhang³, Mohamed E. Madjet², Jennifer Zablocki⁴, Arne Lützen⁴, Jin-Hui Zhong¹, Antonietta De Sio¹, Thomas Frauenheim², Sergei Tretiak³, and Christoph Lienau¹ — ¹University of Oldenburg, Germany — ²University of Bremen, Germany — ³Los Alamos National Laboratory, USA — ⁴University of Bonn, Germany

Squaraines are prototypical quadrupolar charge-transfer chromophores. Their optical properties are often rationalized using an essential state model, predicting that optical transitions to the lowest excited state (S1) are one-photon allowed and to the next higher state (S2) are only two-photon-allowed and that vibronic coupling to high-frequency modes is greatly reduced. Here, we combine time-resolved spectroscopy techniques and quantum-chemical simulations to test and rationalize these predictions. We find the one-photon-allowed S1 and two-photon-allowed S2 states to be energetically well-separated. Also, we find small Huang-Rhys factors, especially for the high-frequency modes. The resulting concentration of the oscillator strength in a narrow spectral region around the S1 transition makes squaraines almost perfect optical two-level. Thus, these molecules and their aggregates are exceptionally interesting for e.g. strong coupling applications. [1]: Timmer, Daniel, et al., J. Am. Chem. Soc., 144, 41, 19150-19162 (2022)