Infrared spectra of 5-fluorouracil molecules isolated in inert Ar matrices, and their films on graphene oxide at 6 K

Abstract

The FTIR spectra of 5-fluorouracil (5FU) molecules isolated in low-temperature (T = 6 K) argon matrices were observed in the infrared range of 3800–200 cm−1. The FTIR spectra of graphene oxide (GO) films on a copper mirror at a temperature of 6 K and the spectra of 5FU films grown on GO films were recorded for the first time. Estimates of the 5FU tautomer population using quantum-mechanical methods DFT/B3LYP and MP2, and calculations of the 5FU vibrational spectra using the DFT/B3LYP/6-311++G(df,pd) method with a correction to the calculated frequencies by a third-order polynomial were performed. It is found that the population of the minor 5FU tautomers at an evaporation temperature of 375 K does not exceed 0.1%. In the spectral range of 1900–500 cm−1 ten 5FU combination modes are registered, which are amplified by the Fermi resonance. In the region of fundamental vibrations νCO, triple Fermi resonance is observed. It is demonstrated that low temperatures have little effect on the spectral characteristics of GO films. Furthermore, multiple thermal cycling between 6 and 295 K does not violate the integrity of the GO films and their thermal contact with the copper mirror. The FTIR spectra of 5FU matrix and film samples grown on different substrates are compared. A gain in the absorption band of thin-film 5FU grown on GO, in comparison to samples grown on a Cu substrate, is recorded. It is established that the infrared spectrum changes when the 5FU deposited on GO film is annealed. The relationship between these spectral changes and the polymorphism of the 5FU crystal structure is discussed.