Work

Distinguishing Polymorphs of the Semiconducting Pigment Copper Phthalocyanine by Solid-State NMR and Raman Spectroscopy

Year: 2010

Type: article

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.

Source: The Journal of Physical Chemistry B

DOI: 10.1021/jp9061412

Authors: Medhat A. Shaibat, Leah B. Casabianca, Diana Y. Siberio-Pérez, Adam J. Matzger, Yoshitaka Ishii

Institutions: University of Michigan, University of Illinois Chicago, University at Albany, State University of New York

Language: English

Topic: Advanced NMR Techniques and Applications

Subfield: Spectroscopy

Field: Chemistry

Domain: Physical Sciences

Open Access status: green

Funder: National Institute on Aging

Award: Molecular Structures and Kinetics of Amyloid Intermediates by Solid-State NMR