Optical Absorption Properties in Pentacene/Tetracene Solid Solutions

Frederik Unger, Daniel Lepple, Maximilian Asbach, Luca Craciunescu, Clemens Zeiser, Andreas F. Kandolf, Zbyněk Fišer, Jakub Hagara, Jan Hagenlocher, Stefan Hiller, Sara Haug, Marian Deutsch, Peter Grüninger, Jiří Novák, Holger F. Bettinger, Katharina Broch, Bernd Engels, Frank Schreiber

Research output: Contribution to journalArticlepeer-review

Abstract

Modifying the optical and electronic properties of crystalline organic thin films is of great interest for improving the performance of modern organic semiconductor devices. Therein, the statistical mixing of molecules to form a solid solution provides an opportunity to fine-tune optical and electronic properties. Unfortunately, the diversity of intermolecular interactions renders mixed organic crystals highly complex, and a holistic picture is still lacking. Here, we report a study of the optical absorption properties in solid solutions of pentacene and tetracene, two prototypical organic semiconductors. In the mixtures, the optical properties can be continuously modified by statistical mixing at the molecular level. Comparison with time-dependent density functional theory calculations on occupationally disordered clusters unravels the electronic origin of the low energy optical transitions. The disorder partially relaxes the selection rules, leading to additional optical transitions that manifest as optical broadening. Furthermore, the contribution of diabatic charge-transfer states is modified in the mixtures, reducing the observed splitting in the 0-0 vibronic transition. Additional comparisons with other blended systems generalize our results and indicate that changes in the polarizability of the molecular environment in organic thin-film blends induce shifts in the absorption spectrum.

Original languageEnglish
Pages (from-to)747-760
Number of pages14
JournalJournal of Physical Chemistry A
Volume128
Issue number4
Early online date17 Jan 2024
DOIs
Publication statusPublished - 1 Feb 2024

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