Raman study on pentacene:C₆₀ bulk heterojunction films

We measured 785 nm excited Raman and infrared spectra of pentacene-d₁₄. The observed spectra were assigned on the basis of the Raman and infrared spectra calculated by the density functional theory (DFT) method at the B3LYP/6-311 + G∗∗level. We measured 785 nm excited Raman spectrum of a pentacne-d₁₄:C₆₀ bulk heterojunction film. The spectrum was assigned on the basis of the wavenumber shifts upon deuteration of pentacene. The assignments of the 1462 and 493 cm^-1 A_g bands of C₆₀ were confirmed. The 511, 453, and 256 cm^-1 bands, which were observed only in pentacene:C₆₀ bulk heterojunction films, did not show large deuteration shifts. This result indicates that the 511, 453, and 256 cm^-1 bands are attributed to activation of the silent modes of C₆₀ due to symmetry lowering_.