Abstract
An enantiomerically pure (R)-2-methylpyrrolidine-based anilino squaraine crystallizes in two chiral polymorphs adopting a monoclinic C2 and an orthorhombic P21 21 21 structure, respectively. By various thin-film preparation techniques, a control of the polymorph formation is targeted. The local texture of the resulting textured thin films is connected to the corresponding optical properties. Special attention is paid to an unusual Davydov splitting, the anisotropic chiroptical response arising from preferred out-of-plane orientation of the crystallites, and the impact of the polymorph specific excitonic coupling.
Highlights
The advancement of organic opto-electronics relies on the development of robust organic semiconductors suitable for processing into functional thin films
Chiroptical properties such as excitonic circular dichroism (CD)7 are in the spotlight having its added value in opto-electronics in view
Often two or more translationally invariant molecules are present per unit cell enabling a spectrally well-resolved Davydov splitting of the coupled molecular resonance.6,11,23-25Accordingly, we found two chiral polymorphs for an enantiomerically pure (R)-2-methylpyrrolidine-based anilino squaraine ((R,R)-PyrSQ-C1), a monoclinic C2 and an orthorhombic P212121 phase with two and four molecules per unit cell, respectively
Summary
The advancement of organic opto-electronics relies on the development of robust organic semiconductors suitable for processing into functional thin films. Often two or more translationally invariant molecules are present per unit cell enabling a spectrally well-resolved Davydov splitting of the coupled molecular resonance.6,11,23-25Accordingly, we found two chiral polymorphs for an enantiomerically pure (R)-2-methylpyrrolidine-based anilino squaraine ((R,R)-PyrSQ-C1), a monoclinic C2 and an orthorhombic P212121 phase with two and four molecules per unit cell, respectively. Thereby, we focus on the local polymorph specific excitonic coupling on a microscopic scale and attempt to capture the anisotropic chiroptical response by imaging Mueller matrix polarimetry.26,27
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