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Polymorph-Selective Preparation and Structural Characterization of Perylene Single Crystals
journal contribution
posted on 2015-11-04, 00:00 authored by André Pick, Michael Klues, Andre Rinn, Klaus Harms, Sangam Chatterjee, Gregor WitteOrganic semiconductors
occurring in polymorphic structures represent
excellent model systems for fundamental studies of optoelectronic
excitations in different crystalline configurations. Perylene is an
archetypal polycyclic aromatic hydrocarbon appearing in two polymorphs
known as α- and β-phases which adopt different molecular
packing motifs. However, the growth of high quality single crystals
with appropriate sizes and polymorph selectivity remains challenging.
In this study, we compare various approaches toward polymorph-selective
perylene single-crystal growth. Though crystals of both polymorphs
are obtained from toluene solution (either by cooling of a saturated
solution or by evaporation of the solvents), they exhibit numerous
defects and their size cannot be precisely controlled. Vapor deposition
and resublimation favor the formation of α-crystals which can
be rationalized by a newly identified thin-film phase that forms initially.
Further, we demonstrate that organic molecular beam deposition onto
silicone-oil-covered substrates enables the fabrication of high-quality
crystals of both phases. The relative occurrence of the individual
polymorphs is controlled by the actual deposition parameters. Combining
the results of X-ray diffraction, atomic force microscopy, and fluorescence
analysis enables an unambiguous polymorph identification solely based
on the characteristic crystal shape. The morphological characterization
reveals characteristic screw dislocations at crystals grown from solution
or by resublimation while the liquid-mediated crystals exhibit exceptionally
flat surfaces and enable detailed fluorescence studies without defect-related
emission signals.
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Vapor depositionpolymorph identificationfluorescence analysisarchetypal polycyclicoptoelectronic excitationsresublimation favorpolymorphic structurescrystal shapescrew dislocationstoluene solutionPerylene Single CrystalsOrganic semiconductorspolymorph selectivitydeposition parametersfluorescence studiesmodel systemsbeam depositionStructural Characterizationforce microscopyphase
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