  We use photoemission spectroscopy to study electronic structures of pristine
and K-doped solid picene. The valence band spectrum of pristine picene consists
of three main features with no state at the Fermi level (EF), while that of
K-doped picene has three structures similar to those of pristine picene with
new states near EF, consistent with the semiconductor-metal transition. The
K-induced change cannot be explained with a simple rigid-band model of pristine
picene, but can be interpreted by molecular orbital calculations considering
electron-intramolecular-vibration interaction. Excellent agreement of the
K-doped spectrum with the calculations points to importance of
electron-intramolecular-vibration interaction in K-doped picene.
