Electronic Structures of Nucleosides as Promising Functional Materials for Electronic Devices

The energy level alignments of nucleosides fabricated between conventional Al and indium tin oxide (ITO) electrodes by means of a vacuum electrospray deposition technique were investigated using in situ ultraviolet and X-ray photoelectron spectroscopy measurements. The electronic structures of four nucleosides - deoxyguanosine, deoxyadenosine, deoxycytidine, and deoxythymidine - were determined, and their interactions with Al and ITO were analyzed. When in contact with ITO, each nucleoside showed an interface dipole that reduced the work function. On the other hand, when Al was deposited on the nucleoside layers, strong chemical interactions were observed due to electron transfer from Al to the nucleosides. Compared to their nucleobase counterparts, nucleosides commonly had lower ionization energies (IEs) and electron affinities (EAs). The origin of this difference in electronic structure was analyzed with density functional theory calculations. The sugar moieties in the nucleosides were found to induce electron-donating effects on the base moiety and led to reductions in IE and EA.