Beschreibung:
<jats:sec><jats:label /><jats:p>Temperature‐dependent and spatially resolved photoluminescence (PL) spectroscopy is employed to probe the optical properties of spin‐cast squaraine thin films annealed to different temperatures. SQIB, a squaraine derivative with donor–acceptor–donor configuration, crystallizes in monoclinic and orthorhombic structures at low and high temperatures, respectively. The former is characterized by an optical response typical for H‐aggregates, while the latter shows J‐type behavior. In temperature‐dependent PL spectra, the two polymorphs are identified via their specific vibrational signature. Spatially resolved data taken with 5 μm resolution give insight into the homogeneity of the SQIB films. The high‐temperature films are made of uniform J‐type crystallites of 50–100 μm size, as also seen in polarization‐dependent data. The low‐temperature films comprise a mixture of grains with H‐ and J‐character. Their specific spectral fingerprints superimpose to the overall emission response detected in the global PL spectra. The study demonstrates that the optical properties of SQIB thin films can be probed at the level of individual grains and systematically modified by thermal treatment.</jats:p></jats:sec>