Polymorphic chiral squaraine crystallites in textured thin films

Abstract

An enantiomerically pure (R)-2-methylpyrrolidine-based anilino squaraine crystallizes in two chiral polymorphs adopting a monoclinicC2 and an orthorhombic P212121structure, respectively. By various thin-film preparation tech-niques, a control of the polymorph formation is targeted. The local texture ofthe resulting textured thin films is connected to the corresponding opticalproperties. Special attention is paid to an unusual Davydov splitting, the aniso-tropic chiroptical response arising from preferred out-of-plane orientation ofthe crystallites, and the impact of the polymorph specific excitonic coupling.