Design of a triplet arylnitrenium ion photoprecursor and time-resolved spectroscopic studies of hydrazinium salts in acetonitrile and water

Abstract

In this thesis, phenylhydrazine 24 and 4-iodophenylhydrazine 28 were synthesized. These were detected and confirmed by NMR and mass spectroscopy and also the corresponding four phenylhydrazinium salts (25, 26, 29 and 30) were obtained and characterized by the same methods. Moreover, to compare their photophysical and thermal properties, Uv-vis absorption spectroscopy, emission spectroscopy, FT-IR and TGA were also employed and studied for these compounds. The UV-vis absorption of phenylhydrazinium tetrafluoroborate 25 and phenylhydrazinium chloride 26 differ from that of phenylhydrazine 24 in MeCN and water:MeCN(1:1) where the two salts show a hypsochromic shift. Likewise, the 4-iodophenylhydrazinium tetrafluoroborate 29 and 4-iodophenylhydrazinium chloride 30 were compared with 4-iodophenylhydrazine 28 and they exhibit a similar phenomenon. In addition, the four salts (25, 26, 29, and 30) were also compared. The compounds 29 and 30 show a bathochromic shift compared with 25 and 26 in water and water:MeCN(1:1). For the emission spectroscopy, there is fluorescence for the salts 25 and 26, while 29 and 30 have no emission. Furthermore, photoproduct studies were conducted for these compounds. Under the UV light irradiation, the 4-iodophenylhydrazinium tetrafluoroborate 29 and phenylhydrazinium tetrafluoroborate 25 can have photoreaction in MeCN in which the color changed from a clear solution into a yellow one. Both the UV-vis absorption spectra and TLC can help assure the occurrence of the reaction and the generation of the new products. Their photoproducts differentiation is very important to help observe and characterize the key transient intermediates that determine the photoreaction mechanism. Finally, time-resolved transient absorption methods were used to investigate 29 and the triplet 4-iodophenylnitrenium ion 331 was directly observed and studied. These results can have significant meaning since most arylnitrenium ions are characterized by the singlet state while seldom are triplet arylnitrenium ions investigated. Therefore, through this research, the triplet 4-iodophenylnitrenium ion 331 would shed new light on the triplet arylnitrenium ion reactivity in reactions examined in the future.