Hydrogen bonding interactions in two isomers of fluorobenzoylthioureas and their absorption spectra

Crystal structures of two benzoylthiourea isomers, named N-4-fluorobenzoyl-N′-4-tolylthiourea (FBTT4) and N-2-fluorobenzoyl-N′-2-tolylthiourea (FBTT2) were determined by X-ray diffraction method. It was found that intra- and intermolecular hydrogen bonds played an essential role in determining their conformations. Electronic spectra of these two isomers (FBTTs) were investigated by UV absorption spectra. The UV absorption bands indicating n → π* transition become widened due to intramolecular hydrogen bonds, while intermolecular hydrogen bonds between FBTTs and the solvent molecules led to unusual blue shifts of the UV absorption band for π → π* transition. The intensity of UV absorption decreased as increasing the solvent polarity and the formation of intermolecular hydrogen bonds. The absorption spectra of two isomers have been calculated with the TDDFT formalism. The calculated absorption curves by the CPCM model considering the first solvent shell match well with the experimental results.