Accelerated Charge Separation and Stabilization in a Fused Bis Zinc Porphyrin-Quinone Conjugate Via Cation-Quinone Interaction

Abstract

Accelerated singlet excited state charge separation, improved quantum yields, and ultimate charge stabilization upon cation binding to the electron acceptor quinone in a fused bis zinc porphyrin-quinone (zinc porphyrin located on each side of the pentacenequinone) donor-acceptor conjugate has been accomplished. Selective binding of either Mg2+ or Sc3+ to quinone in the donor-acceptor conjugate led to facile reduction of quinone making the charge separation process thermodynamically more feasible. Consequently, increased population of the charge separated state was witnessed in femtosecond transient absorption studies with a near linear trend in population of the charge separated state versus amount of metal-ion added. GloTarAn software was utilized to process the spectral data which enabled determination of the species associated spectrum and population profiles which thereby allowed deconvolution of the femtosecond spectral data and appropriate designations of each state. The present findings may provide further insight into the role of the interaction between quinones and iron metal ions in the electron transport chain of natural photosynthesis, which may have further implications in other biological systems where metal cations are present in electron transport chains.