CIDNP Effects of Sensitized Photochemical Dediazoniation of Arene Diazonium Salts Manipulating CIDNP Intensities by the Experimental Conditions

Abstract

13C and 15N photo-CIDNP effects were determined for the reversible electron transfer from pyrene to arene diazonium salts on excitation of the charge transfer band at 360 nm. The diazonium salts being the products of back electron transfer (“cage products”) show enhanced absorption for 13 C(1) and the 15N-enriched diazonium group, whereas the escape products, ArH or 15N2, respectively, yield emission signals. It was shown that the intensities of the CIDNP effects depend on the rates of intersystem crossing kisc within the geminate radical pair, i.e. on the magnetic nucleus used as a probe of the CIDNP effect. Using 1H, 13C or 15N the time domain of observation can be manipulated in the ranges of 90-100 ns, 15-20 ns and 3-5 ns, respectively. Furthermore, the CIDNP intensities depend on the proper balance of the rate of electron back transfer, k-e, and the rate kp of formation of the escape product. Since k-e increases with increasing energy of the geminate radical pair, this balance and therefore the CIDNP intensities vary according to the substituent present and the electron donor used