Abstract
The optical properties of organic materials are very sensitive to subtle structural modification, and a proper understanding of the structure-property relationship is essential to improve the performance of organic electronic devices. The phase transitions of the η-CuPc to the α-CuPc, then to the β-CuPc were investigated using In situ X-ray diffraction and the differential scanning calorimetry (DSC). The five stages in the phase-transition process from low to high-temperature were observed, which consisted of (1) the η-CuPc; (2) a mixture of the η- and α-CuPc; (3) a mixture of the η-, α- and β-CuPc; (4) a mixture of the α- and β-CuPc; and (5) the β-CuPc. The vibrational and optical properties at different phase-transition stages were correlated to molecular packing motif and molecule overlap type through systematic analyses of the Fourier–transform infrared, Raman and UV-VIS spectra. Moreover, the mechanism for the morphology evolution was also discussed in detail.
Highlights
Organic nanomaterials have been widely used in the fabrication of electronic devices over the last few decades, such as organic field-effect transistors (OFET) [1], organic photovoltaics (OPV) [2]and sensors [3]
These extensive application prospects require a proper understanding of the effect of fundamental aspects in crystal structure, such as molecular packing motifs and molecular orbital overlap, on the performance of organic electronic devices
Since the crystal structure is known to have a significant impact on the performance of organic electronic devices, the identification and manipulation of molecular packing motifs and molecular overlap type are important for optimization of materials properties
Summary
Organic nanomaterials have been widely used in the fabrication of electronic devices over the last few decades, such as organic field-effect transistors (OFET) [1], organic photovoltaics (OPV) [2]. These extensive application prospects require a proper understanding of the effect of fundamental aspects in crystal structure, such as molecular packing motifs and molecular orbital overlap, on the performance of organic electronic devices. For planar small molecules, such as copper-phthalocyanine (CuPc), molecular packing motifs, typically herringbone and parallel (lamellar) packings, will significantly influence the inter-molecular overlaps and transfer integrals and, the optical and electrical properties, which determine the performance characteristics of organic electronic devices [4,5]. Both rubrene and pentacene have herringbone packing motifs, rubrene shows a higher carrier mobility owing to a larger co-facial π-π overlap [5,6].
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