Sensitivity boosting in solid-state NMR of thin organic semiconductors by a paramagnetic dopant of copper phthalocyanine

Sensitivity enhancements in cross-polarization magic-angle-spinning (CPMAS) solid-state NMR spectra of organic thin-film semiconductors are reported. A vacuum-deposited paramagnetic dopant on the semiconductor films reduces 1H T1 relaxation time, enabling faster repetition of NMR measurements. When the thickness of the films is between 50 and 100 nm, 1H spins are well polarized by 1H–1H spin diffusion, giving the maximum sensitivity without harmful effects such as paramagnetic shift, broadening, and quenching of CPMAS signals. The binary films of copper phthalocyanine (CuPc) and phenyldipyrenylphosphine oxide (POPy2) show a threefold reduction of the NMR measurement time.