Two neutral pyrazolato diimine rhenium(I) carbonyl complexes with formula [Re(CO)3(N-N)(btpz)] where N-N = 2,2‘-bipyridine (1) and 1,10-phenanathroline (2), and btpz = 3,5-bis(trifluoromethyl) pyrazolate, were synthesized and characterized by elemental analysis, routine spectroscopic methods, and single-crystal X-ray diffraction study. Ground and excited state properties of these complexes were investigated by steady-state and time-resolved spectroscopies. Complexes 1 and 2 show photoluminescent emission in both solution and solid-state at room temperature, arising from metal to ligand charge-transfer (MLCT) transition with strong overlapping of intraligand π → π* transitions. The long-lived excited state lifetimes of complexes 1 and 2, which are on the order of microseconds, indicate the presence of phosphorescent emission. As these complexes hold the potential to serve as phosphors for organic light-emitting diodes (OLEDs), their electroluminescent performances were evaluated by employing them as dopant...

Realizing Green Phosphorescent Light-Emitting Materials from Rhenium(I) Pyrazolato Diimine Complexes

Excited-state equilibration: a process leading to long-lived metal-to-ligand charge transfer luminescence in supramolecular systems

Transition metal complexes having metal-to-ligand charge transfer (MLCT) excited states have been extensively investigated as sensitizers in light-induced electron transfer reactions. The photophysical behavior of the complexes is strongly dependent on the ligand serving as the electron acceptor. In systems where ligand localized triplet excited states are close in energy to the thermally equilibrated 3 MLCT state, strong interaction between the states is observed. This article provides an overview of the unique photophysical behavior observed in systems of this type.

Photophysical behavior of transition metal complexes having interacting ligand localized and metal-to-ligand charge transfer states

This review describes recent advances in the photochemistry of complexes of the element rhenium. It covers not only fundamental chemistry but the recent applications of these complexes to supramolecular chemistry, carbon dioxide reduction, bioinorganic chemistry, sensors, and light-emitting devices.

Photochemistry and Photophysics of Coordination Compounds: Rhenium

A simple design strategy for a new class of stable, vacuum-sublimable, and strongly emissive sky-blue neutral phosphorescent Re(I) phenanthroline complexes {Re(R2phen)(CO)3[CNB(C6F5)3]} is reported. These complexes show intense bluish green emission in CH2Cl2 solution with the highest emission quantum yield and bluest emission ever reported for the neutral Re(I) diimine complexes. In the solid state, they display sky-blue emission. The electroluminescent properties of devices containing these complexes have also been investigated.

A Simple Design for Strongly Emissive Sky-Blue Phosphorescent Neutral Rhenium Complexes: Synthesis, Photophysics, and Electroluminescent Devices

Excited state properties of the newly prepared complexes R–CO2–Re(CO)3(2,2′-bipy), where R–CO2−
= naphthalene-2-carboxylate, anthracene-9-carboxylate, pyrene-1-carboxylate and acetate, were investigated by steady state and time resolved spectroscopy The X-ray structure revealed that the R containing ligand is coordinated through the carboxylate group to Re(I) Results showed that two emitting excited states play a major role in the photophysics of the complexes The fast component of the complexes luminescence was associated with the charge transfer excited state, MLCT, Re-to-2,2′-bipyridine, while experimental evidence led to the long lived component being attributed to a ligand-to-ligand charge transfer excited state This emissive LLCT excited state can also evolve to a photodissociative state which ultimately produces the complex decarboxylation On the other hand, the carboxylate
bridge was shown to be able to impede connection between R and the Re(CO)3(2,2′-bipy) chromophore

J. Tocho

Papers

Photoinduced charge separation in R–CO2–Re(CO)3(2,2′-bipyridine) complexes. Two emitting charge transfer excited states