Partial Hydrogenation of N-Heteropentacene upon Vacuum Deposition

Four-nitrogen-containing 5,6,13,14-tetraazapentacene (BTANC) is a new n-type organic semiconductor with a rigid crystalline phase due to intermolecular C-H···N hydrogen bonding. However, so far, poor carrier transport properties and low stability in ambient conditions have been reported for BTANC thin-film transistors, which calls for further understanding of the film state of BTANC. Here, we investigated the detailed electronic and structural properties of the vacuum-deposited film of BTANC, utilizing a well-defined monolayer on Cu(111). From the photoemission spectra of the deposited films, the alteration of the chemical state of nitrogen atoms in BTANC was noted, suggesting the partial hydrogenation of nitrogen atoms during the vacuum deposition. In addition, the monolayer did not show the expected molecular packing for the hydrogen-bonded BTANC due to the emergence of intermolecular N-H···N hydrogen bonding between hydrogenated molecules. This work serves as a general remark in fabricating the films of the nitrogen-containing acene molecular films.