Photochemical Generation of Polymeric Alkyl-C60 Radicals:  ESR Detection and Identification

• Published in: The journal of physical chemistry. B Vol. 105; no. 11; pp. 2129 - 2134
• Main Authors: Qu, Baojun, Hawthorn, Geoff, Mau, Albert W. H, Dai, Liming
• Format: Journal Article
• Language: English
• Published: American Chemical Society 22.03.2001
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp002666l

Electron spin resonance (ESR) spectroscopy has been used to study various alkylfullerene radical adducts generated by UV-photoinitiated reactions between low-density polyethylene (LDPE) and C60 in the presence or absence of benzophenone (BP) as a photoinitiator under different conditions. Photolysis of LDPE/BP/C60 mixture in toluene at 323 K produced benzylfullerene (RC60) radical adducts, showing a strong ESR signal of g = 2.002 70 with several well-resolved pairs of 13C satellites. On the other hand, a well-resolved ESR spectrum characteristic of polymeric alkylfullerene (PC60) radical adducts was observed during UV irradiation of the LDPE/BP/C60 in benzene or in the molten state (413 K). Detailed analyses of hyperfine structures (hfs) revealed that the ESR spectrum for PC60 radical adducts consisted of three components:  (1) a broad singlet at g = 2.002 50 arising from C60 radical anions; (2) an innermost pair of 13C satellites; and (3) a 12-line spectrum superimposed on the broad singlet. Spectroscopic simulation allowed the 12-line spectrum to be attributed to the coexistence of two polymeric radical adducts of C60 (i.e., the tertiary carbon radical adduct, −(CH2)3C-C60 •, designated as PAC60 •, and the secondary carbon radical adduct, −(CH2)2CH-C60 •, designated as PBC60 •), which have slightly different g values (g A = 2.002 48 and g B = 2.002 44) and integral intensities I A/I B (48.4/51.6). These results clearly indicated the generation of C60-bonded LDPE materials simply by photoirradiation of LDPE/C60 with BP as a photoinitiator.