Abstract
Atomic/molecular layer deposition (ALD/MLD) offers unique possibilities in the fabrication of inorganic-organic thin films with novel functionalities. Especially, incorporating nucleobases in the thin-film structures could open new avenues in the development of bio-electronic and photonic devices. Here we report an intense blue and widely excitation-dependent fluorescence in the visible region for ALD/MLD fabricated sodium-uracil thin films, where the crystalline network is formed from hydrogen-bonded uracil molecules linked via Na atoms. The excitation-dependent fluorescence is caused by the red-edge excitation shift (REES) effect taking place in the red-edge of the absorption spectrum, where the spectral relaxation occurs in continuous manner as demonstrated by the time-resolved measurements.
Highlights
During the last decade, there has been a growing interest in developing new biomaterials for bioelectronics and photonic applications[1, 2]; the driving motivation is to utilize ecologically safe and environmentally sustainable, cheap and renewable material sources for frontier applications[3]
In optoelectronic applications deoxyribonucleic acid (DNA) has been employed as an electron transport layer (ETL) in organic light emitting diodes (OLEDs) and as a gate dielectric in organic field emitting transistors (OFETs)[11, 12]
A schematic presentation of the structure is shown in Fig. 1, along with a typical Fourier-transform infrared (FTIR) spectrum and a grazing-incidence x-ray diffraction (GIXRD) pattern recorded for the films to evidence, respectively, the presence of the targeted organic moieties and the crystallinity of the films
Summary
There has been a growing interest in developing new biomaterials for bioelectronics and photonic applications[1, 2]; the driving motivation is to utilize ecologically safe and environmentally sustainable, cheap and renewable material sources for frontier applications[3]. Compared to the massive interest in DNA, its constituent parts, i.e., the nucleobases (NBs), have received considerably less attention as potential building blocks for bioelectronic material applications This is surprising, as their rich chemical structures can facilitate aromatic stacking and different hydrogen-bonding schemes to create three-dimensional supramolecular assemblies, like in the natural systems[13,14,15]. The smaller size of the NB molecules compared to DNA is a clear advantage when considering their employment as precursors in vacuum-based thin-film deposition techniques[16, 17] Another advantage concerns the better controllability of the desired functionality, as the properties are defined more precisely for the monomeric NBs than for the monumental DNA polymers with only the approximate molecular masses known. The emission takes place from the lowest excited state of given multiplicity regardless of the excitation wavelength, which is known as the Kasha’s rule[30,31,32,33]
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