Muoniated radical states in the organic semiconductor phthalocyanine

Abstract

Phthalocyanine samples of ZnPc, ${\mathrm{H}}_{2}\mathrm{Pc}$, and CuPc were investigated with the muon spin rotation technique. In ZnPc and ${\mathrm{H}}_{2}\mathrm{Pc}$, three muoniated radical states of paramagnetic origin were identified, two of which have hyperfine interactions in the range $110\char21{}150\phantom{\rule{0.3em}{0ex}}\mathrm{MHz}$ and correspond to muonium addition at the outer benzene rings. The third state has a smaller hyperfine interaction (about $25\phantom{\rule{0.3em}{0ex}}\mathrm{MHz}$) and is tentatively assigned to addition at bridging nitrogen atoms. CuPc has an unpaired electron from the Cu atom, which originates a diamagneticlike signal upon muonium addition. The signal has two components with very different relaxation rates, corresponding to two different spatial couplings of the Cu electron with the muonium's electron.