Electrochemistry, Photophysics and Spectroscopy of a New Class of Electron Transfer Quenchers. Crisjoe Joseph & Azam Ahmed

Abstract

A quencher provides two additional routes for the excited species to return to the ground state: energy transfer and electron transfer. This project looks at ruthenium compounds that do not absorb at these high wavelengths and are believed to be excellent reductive quenchers. Cyclopentadienyl ruthenium tris-pyrazolylborate, cyclopentadienyl ruthenium tris-(3-5-dimethyl) pyrazolylborate and pentamethylcyclopentadienyl ruthenium tris-pyrazolylborate will be tested. Stern-Volmer analysis, cyclic voltametry, and transient absorption spectra will be taken and analyzed. From the determined Kq, reductive potentials and transient absorption spectrum, one can ascertain the predominant route of quenching. Along with these ruthenium-boron complexes the ruthenium-carbon analogs (Cyclopentadienyl ruthenium tris-(3-5-dimethyl) pyrazolylmethyl, cyclopentadienyl ruthenium tris-pyrazolylmethyl and cyclopentadienyl ruthenium tris-(3-t-butyl)pyrazolylmethyl) will be synthesized. These compounds are of interest because they should be soluble in water, unlike the ruthenium-boron complexes. It was found from the transient absorption spectrum that the majority of the quenching that occurred because of pentamethylcyclopentadienyl ruthenium tris-pyrazolylborate was occurring through electron transfer. In contrast, cyclopentadienyl ruthenium tris-pyrazolylborate quenched almost exclusively through energy transfer. Both energy transfer and electron transfer played equal paths of quenching due to cyclopentadienyl ruthenium tris-(3-5-dimethyl) pyrazolylborate.