14275-09-3Relevant articles and documents
Enhancement of the Luminescent Efficiency in Carbene-Au(I)-Aryl Complexes by the Restriction of Renner-Teller Distortion and Bond Rotation
Djurovich, Peter I.,Haiges, Ralf,Li, Tian-Yi,Muthiah Ravinson, Daniel Sylvinson,Thompson, Mark E.
, p. 6158 - 6172 (2020)
A series of (carbene)Au(I)(aryl) complexes are reported. The nature of the lowest excited state in these complexes changes character from metal-to-ligand charge transfer (MLCT) to interligand charge transfer (ICT) with increasing electron-donating strength of the aryl ligand. Complexes that have the MLCT lowest excited state undergo a Renner-Teller bending distortion upon excitation. Such a distortion leads to a large rate of nonradiative decay, on the order of 108 s-1. Renner-Teller-based nonradiative decay does not occur in chromophores with an ICT emissive state. Introducing a julolidine moiety and ortho-methyl substituents to the aryl group makes the molecule rigid and hinders the rotation along the Au-Caryl-coordinate bond. Consequently, the nonradiative decay rates of these ICT emitters are decreased and become lower than the radiative decay rate constants (kr = 105 s-1). Thus, high-luminescent efficiencies (φPL = 0.61 and 0.77) along with short lifetimes (τ ST -1) in these emitters.
Spin-Allowed Transitions Control the Formation of Triplet Excited States in Orthogonal Donor-Acceptor Dyads
Buck, Jason T.,Boudreau, Andrew M.,DeCarmine, André,Wilson, Reid W.,Hampsey, James,Mani, Tomoyasu
, p. 138 - 155 (2019)
Reliance on triplet excited states (triplets) of molecules with heavy atoms, such as precious metals, limits their potential in technological applications. We envision that triplets of π-conjugated organic molecules could play bigger roles; however, their production without heavy atoms remains challenging. The direct, spin-forbidden conversion of singlet charge-separated states to triplets in an electron donor-acceptor (D-A) pair is a promising approach. Here, using a series of orthogonal D-A type boron dipyrromethene (BODIPY) derivatives as a model system, we show that the formation of triplets is largely controlled by the spin-allowed transitions. Yet, this spin-forbidden process can still proceed much faster than ordinary intersystem crossing between (π π*) states under favorable conditions because of stronger spin-orbit coupling. Our findings reveal a clear physical basis for this spin-forbidden process and provide guidelines for future molecular designs exploiting the process. Production of triplet excited states of π-conjugated organic molecules in high yields without using heavy atoms remains challenging. The direct formation of triplet excited states from singlet charge-separated states is a promising approach. Here, we show that spin-allowed electron-transfer reactions largely control such a formation, yet the spin-forbidden transition can outcompete the spin-allowed transitions under favorable conditions because of stronger spin-orbit coupling. Triplet excited states (triplets) serve as key intermediates in critical technologies and processes ranging from organic synthesis to biomedicine to molecular electronics. Production of triplets of π-conjugated organic molecules without heavy atoms remains challenging. Spin-orbit, charge-transfer intersystem crossing (SOCT-ISC) directly converts singlet charge-separated states to triplets in an electron donor-acceptor (D-A) pair. Here, using a series of orthogonal D-A type boron dipyrromethene (BODIPY) derivatives as a model system, we show that the formation of triplets is largely controlled by the spin-allowed transitions rather than by SOCT-ISC. Yet, the SOCT-ISC process can still proceed much faster than ordinary ISC between (π π*) states because the spin-orbit coupling of SOCT-ISC is 2 orders of magnitude stronger. We further show that such a process can produce triplets in a non-triplet-forming molecule, perylene. Our findings reveal a clear physical basis for this spin-forbidden process and provide guidelines for future molecular designs exploiting the process.
Role of substitution on the photophysical properties of 5,5′-diaryl-2,2′-bipyridine (bpy*) in [Ir(ppy) 2(bpy*)]PF6 complexes: A combined experimental and theoretical study
Ladouceur, Sebastien,Fortin, Daniel,Zysman-Colman, Eli
scheme or table, p. 5625 - 5641 (2010/08/04)
The synthesis of a family of 4′-functionalized 5,5′-diaryl-2, 2′-bipyridines (bpy*; 6a-6g) is reported. These ligands were reacted with the dimer [(ppy)2IrCl]2 (ppyH = 2-phenylpyridine) and afforded, after subsequent counterion exchange, a new series of luminescent cationic heteroleptic iridium(III) complexes, [(ppy)2Ir(bpy*)] PF6 (8a-8g). These complexes were characterized by electrochemical and spectroscopic methods. The crystal structures of two of these complexes (8a and 8g) are reported. All of the complexes except for 8c and 8f exhibit intense and long-lived emission in both 2-MeTHF and ACN at 77 K and room temperature. The origin of this emission has been assigned by computational modeling to be an admixture of ligand-to-ligand charge-transfer [3LLCT; π(ppy) → π*(bpy*)] and metal-to-ligand charge-transfer [ 3MLCT; dπ(Ir) → π*(bpy*)] excited states that are primarily composed of the former. The luminescent properties for 8a-8c are dependent upon the functionalization at the 4′ position of the aryl substituents affixed to the diimine ligand, while those for 8d-8g are essentially independent because of an electronic decoupling of the aryls and bpy due to the substitution of o,o-dimethyl groups on the aryls, causing a near 90° angle between the aryl and bipyridyl moieties. A combined density functional theory (DFT)/time-dependent DFT study was conducted in order to understand the origin of the transitions in the absorption and emission spectra and to predict accurately emission energies for these complexes.
