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  • Distinguishing polymorphs of the semiconducting pigment copper phthalocyanine by solid-state NMR and Raman spectroscopy.

Distinguishing polymorphs of the semiconducting pigment copper phthalocyanine by solid-state NMR and Raman spectroscopy.

The journal of physical chemistry. B (2010-03-17)
Medhat A Shaibat, Leah B Casabianca, Diana Y Siberio-Pérez, Adam J Matzger, Yoshitaka Ishii
ABSTRACT

Cu(II)(phthalocyanine) (CuPc) is broadly utilized as an archetypal molecular semiconductor and is the most widely used blue printing pigment. CuPc crystallizes in six different forms; the chemical and physical properties are substantially modulated by its molecular packing among these polymorphs. Despite the growing importance of this system, spectroscopic identification of different polymorphs for CuPc has posed difficulties. This study presents the first example of spectroscopic distinction of alpha- and beta-forms of CuPc, the most widely used polymorphs, by solid-state NMR (SSNMR) and Raman spectroscopy. (13)C high-resolution SSNMR spectra of alpha- and beta-CuPc using very-fast magic angle spinning (VFMAS) at 20 kHz show that hyperfine shifts sensitively reflect polymorphs of CuPc. The experimental results were confirmed by ab initio chemical shift calculations. (13)C and (1)H SSNMR relaxation times of alpha- and beta-CuPc under VFMAS also showed marked differences, presumably because of the difference in electronic spin correlation times in the two forms. Raman spectroscopy also provided another reliable method of differentiation between the two polymorphs.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Copper(II) phthalocyanine, β-form, Dye content 90 %
Sigma-Aldrich
Copper(II) phthalocyanine, sublimed grade, Dye content 99 %
Sigma-Aldrich
Copper(II) phthalocyanine, Dye content >99 %
Sigma-Aldrich
Copper(II) phthalocyanine, triple-sublimed grade, >99.95% trace metals basis