Mapping the Optical Landscape of a Squaraine Molecule in the Visible and Ultraviolet Energy Range

Narges Taghizade; Robert Schwarzl; Frederik Leinenbach; Maximilian Jeindl; Marvin F. Schumacher; Brunella Bardi; Arne Lützen; Manuela Schiek; Andreas W. Hauser; Peter Puschnig; Markus Koch; Andreas Windischbacher

arXiv · 2512.14630

Mapping the Optical Landscape of a Squaraine Molecule in the Visible and Ultraviolet Energy Range

Narges Taghizade·Robert Schwarzl·Frederik Leinenbach·Maximilian Jeindl·Marvin F. Schumacher·Brunella Bardi·Arne Lützen·Manuela Schiek·Andreas W. Hauser·Peter Puschnig·Markus Koch·Andreas Windischbacher

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Abstract

Although squaraine dyes are commonly praised as candidates for light-based applications, little is known about their excited state landscape beyond the low-energy visible light region. Our work aims for an improved understanding of the photophysical properties of squaraines at the example of N-isobutyl substituted anilino-squaraine (SQIB) by extending ground-state and excited-state absorption spectroscopy of the molecule into the ultraviolet up to 6.5~eV. In addition, we distinguish the relative transition dipole moments of the excited state absorption peaks with the help of transient absorption anisotropy experiments. To relate experimental features to specific states, we employ a set of ab initio methods including time-dependent density functional theory (TDDFT), the Bethe-Salpeter equation (BSE) and n-electron valence perturbation theory on top of a self-consistent complete active space (CASSCF/NEVPT2). Our assignment is complemented by vibronic simulations and a discussion of two-photon absorption measurements. Through this joint effort, we are able to provide a consistent picture of the optical behavior of SQIB across the visible and ultraviolet light regime, and assign a total of twelve electronically excited states to our experimental data.

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Narges Taghizade, Robert Schwarzl, Frederik Leinenbach, Maximilian Jeindl, Marvin F. Schumacher, Brunella Bardi, Arne Lützen, Manuela Schiek, Andreas W. Hauser, Peter Puschnig, Markus Koch, Andreas Windischbacher. 2025-12-16. Mapping the Optical Landscape of a Squaraine Molecule in the Visible and Ultraviolet Energy Range. https://arxiv.org/abs/2512.14630

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