Tuning of excited state reduction potentials via expanded π-systems. Synthesis and characterization of [Ru(2,3-di(2′-pyridyl)benzo(g)quinoxaline)3](PF6)2

Mechanism of the Photochemical Ligand Substitution Reactions of fac-[Re(bpy)(CO)3(PR3)]+ Complexes and the Properties of Their Triplet Ligand-Field Excited States

“…Nonradiative decay processes for various types of transition-metal complexes have been investigated by using the energy gap law . Casper and Meyer have reported that there is a good linear relationship between the energy gap and the ln “ k d ” values, which are “nonradiative decay rate constants from 3 MLCT of [Re(X 2 bpy)(CO) 3 Y] n + ” calculated from only emission quantum yields, lifetimes, and emission energies 25a. However, Casper and Meyer did not consider the participation of decay from the 3 LF excited state even though they used a [Re(bpy)(CO) 3 (PR 3 )] + complex.…”

“…Rhenium diimine complexes of the type fac -[Re I (LL)(CO) 3 L‘] n + ( n = 0, 1; LL = diimine ligand) have been well studied because they are excellent emitters, ,− photocatalysts, ,− and building blocks for supramolecules. ,− Although a tremendous number of fundamental studies of the photophysics of these rhenium complexes have been carried out over the last two decades, the targets of these studies have been only triplet CT excited statessuch as metal-to-ligand ( 3 MLCT), ,− ligand-to-ligand ( 3 LLCT), , and σ-to-ligand ( 3 σ−π*) 2,27-29 statesand 3 LC excited states. − In contrast, little is known about the LF states of these rhenium diimine complexes. To our knowledge, only one report discusses their triplet ligand-field ( 3 LF) states: this report reveals that the emission lifetimes of fac -[Re(LL)(CO) 3 (CNR)] + complexes strongly depend on temperature and that the temperature-dependence profiles can be fitted by means of a model based on three thermally accessible excited states: 3 MLCT, 3 LC, and 3 LF .…”

Ni(II) and Ru(II) Schiff base complexes as catalysts for the reduction of benzene

“…Therefore the ligand is susceptible to easy oxidation and reduction, which might be the reason for the formation of the ruthenium(II) complex. The less negative value of reduction potential for this ligand compared to other pyrazine derivatives, such as 2,3-bis(2 -pyridyl)-pyrazine (E 1/2 = −1.80 V), 2,3-bis(2 -pyridyl)-quinoxaline (E 1/2 = −1.43 V), 2,3-di(2 -pyridyl)(benzo(g)quinoxaline) (E 1/2 = −1.29 V) and 6,7dichloro-2,3-bis(2 -pyridyl)-quinoxaline (−1.18 V) [42][43][44], may be due to the presence of the oxygen atoms directly bonded to the pyrazine ring of the ligand. Cyclic voltammogram of the ruthenium complex shows two quasi-reversible redox processes occurring at negative potential and with a peak-to-peak separation ( E p value) of 182 and 209 mV respectively [22].…”

Zn Coordination and the Identity of the Halide Ancillary Ligand Dramatically Influence the Excited-State Dynamics and Bimolecular Reactions of 2,3-Di(pyridin-2-yl)benzo[g]quinoxaline

“…Coordination complexes of 2,3-di­(pyridin-2-yl)­pyrazine (dpp), 2,3-di­(pyridin-2-yl)­quinoxaline (dpq), and 2,3-di­(pyridin-2-yl)­benzo­[ g ]­quinoxaline ( dpb , shown in Figure ) with several first-row transition metals were first reported in the late 1950s and late 1960s. Interest in the photophysical properties of coordination compounds featuring dpp, dpq, and dpb ligands was stimulated in the late 1980s by a number of reports investigating the photophysical and redox properties of transition-metal complexes containing dpp − and dpq. − In the 3 decades that have followed, metal complexes utilizing dpp, dpq, and dpb as diimine-type ligands have been extensively studied and have found application in a multitude of research areas, including photodynamic therapy (PDT), − DNA sensing, − catalysis, − electron-transfer systems, − near-IR light absorbers, − biologically active complexes, − and electroluminescent devices. − Additionally, modified versions of these ligands have been studied for use as monomer units in specialty polymers, , and starburst-shaped analogues have shown promise as electron-transport materials in organic light-emitting diodes (OLEDs) and other optoelectronic devices because of their ability to form stable amorphous molecular glasses. − …”