Excited-State Electron Transfer in a Chromophore−Quencher Complex. Spectroscopic Identification of a Redox-Separated State

Abstract

In the chromophore-quencher complex fac-[Re(Aqphen)(CO)(3)(py-PTZ)](+) (Aqphen is 12,17-dihydronaphtho[2,3-h]dipyrido[3,2-a:2',3'-c]-phenazine-12,17-dione; py-PTZ is 10-(4-picolyl)phenothiazine), Aqphen is a dppz derivative, containing a pendant quinone acceptor at the terminus of a rigid ligand framework. This introduces a third, low-lying, ligand-based pi acceptor level localized largely on the quinone fragment. Laser flash excitation of fac-[Re(Aqphen)(CO)(3)(py-PTZ)](+) (354.7 nm; in 1,2-dichloroethane) results in the appearance of a relatively long-lived transient that decays with tau(298K) = 300 ns (k = 3.3 x 10(6) s(-)(1)). Application of transient absorption, time-resolved resonance Raman, and time-resolved infrared spectroscopies proves that this transient is the redox-separated state fac-[Re(I)(Aqphen(*)(-)())(CO)(3)(py-PTZ(*)(+)())](+) in which the excited electron is localized largely on the quinone portion of the Aqphen ligand.

A novel cobalt complex for enhancing amperometric and impedimetric DNA detection

“…3). The aqphen ligand is known to possess two one-electron reductions (to the semiquinone and diol, respectively) [31] and therefore the most easily accessible reduction was attributed to the Co(III)/Co(II) couple.…”

Comparative evaluation of the acceptor properties of quinone derivatized polypyridinic ligands

“…grade and were used without further purification. Regarding the ligand synthesis, Aqphen and Nqphen were synthetized as described previously [5][6][7] while Pptd was synthesized according to Black and MacGuire. [8c] The model ligand ppl was also synthesized according to reported procedures [9]. Cyclic voltammetry measurements were carried out using a BAS 50 W potentiostat.…”

“…During the last years our group has focused part of its research on the synthesis and characterization of different quinone derivatized polypyridinic ligands with acceptor character, and their corresponding metal complexes: 12,17-dihydronaphtho- [2,3-h] dipyrido[3,2-a:2 0 ,3 0 -c]-phenazine-12,17-dione, Aqphen [5,6], dipyrido[3,2-a:2 0 ,3 0 -c]benzo [3,4]-phenazine-11,16-quinone, Nqphen [7], uracil(5,6-diamino-1,3-dimethyl), Pptd [8], Scheme 1.…”

“…Their difference lies on the type and relative position of the corresponding quinonic groups. Therefore, after receiving an electron, by direct reduction, or by MLCT (metal-ligand change transfer) excitation if forming part of a complex, they should behave as a ''three step cascade" with a p * ordering level following p * (phenanthroline) > p * (phenazine or pyrazine) > p * (quinone portion) [5]. In this paper a comparative study of the three mentioned ligands, as well as the model ligand, pyrazino [2,3-f] [1,10]-phenanthroline, ppl, is presented and discussed.…”

A Screen Printed Phenanthroline-Based Flexible Electrochemical Sensor for Selective Detection of Toxic Heavy Metal Ions

“…QDPPZ was chosen because of several of its characteristics. The structure of QDPPZ reveals high conjugation, which lowers the HOMO-LUMO gap, thus allowing excitation of electrons with lower energy [28]. This compound also contains a quinone group, which is known for its reversible redox chemistry, and exhibits two-electron reduction and oxidation [29].…”