1227073-47-3Relevant academic research and scientific papers
Fluorescence in rhoda- and iridacyclopentadienes neglecting the spin-orbit coupling of the heavy atom: The ligand dominates
Steffen, Andreas,Costuas, Karine,Boucekkine, Abdou,Thibault, Marie-Helene,Beeby, Andrew,Batsanov, Andrei S.,Charaf-Eddin, Azzam,Jacquemin, Denis,Halet, Jean-Francois,Marder, Todd B.
, p. 7055 - 7069 (2014/07/22)
We present a detailed photophysical study and theoretical analysis of 2,5-bis(arylethynyl)rhodacyclopenta-2,4-dienes (1a-c and 2a-c) and a 2,5-bis(arylethynyl)iridacyclopenta-2,4-diene (3). Despite the presence of heavy atoms, these systems display unusually intense fluorescence from the S 1 excited state and no phosphorescence from T1. The S 1 → T1 intersystem crossing (ISC) is remarkably slow with a rate constant of 108 s-1 (i.e., on the nanosecond time scale). Traditionally, for organometallic systems bearing 4d or 5d metals, ISC is 2-3 orders of magnitude faster. Emission lifetime measurements suggest that the title compounds undergo S1 → T1 interconversion mainly via a thermally activated ISC channel above 233 K. The associated experimental activation energy is found to be ΔH ISC? = 28 kJ mol-1 (2340 cm -1) for 1a, which is supported by density functional theory (DFT) and time-dependent DFT calculations [ΔHISC ?(calc.) = 11 kJ mol-1 (920 cm-1) for 1a-H]. However, below 233 K a second, temperature-independent ISC process via spin-orbit coupling occurs. The calculated lifetime for this S1 → T1 ISC process is 1.1 s, indicating that although this is the main path for triplet state formation upon photoexcitation in common organometallic luminophores, it plays a minor role in our Rh compounds. Thus, the organic π-chromophore ligand seems to neglect the presence of the heavy rhodium or iridium atom, winning control over the excited-state photophysical behavior. This is attributed to a large energy separation of the ligand-centered highest occupied molecular orbital (HOMO) and lowest unoccupied MO (LUMO) from the metal-centered orbitals. The lowest excited states S1 and T 1 arise exclusively from a HOMO-to-LUMO transition. The weak metal participation and the cumulenic distortion of the T1 state associated with a large S1-T1 energy separation favor an organic-like photophysical behavior.
2,5-Bis(p-R-arylethynyl)rhodacyclopentadienes Show Intense Fluorescence: Denying the Presence of a Heavy Atom
Steffen, Andreas,Tay, Meng Guan,Batsanov, Andrei S.,Howard, Judith A. K.,Beeby, Andrew,Marder, Todd B.,Vuong, Khuong Q.,Sun, Xue-Zhong,George, Michael W.
, p. 2349 - 2353 (2010/06/15)
Heavy-metal light show: Photophysical studies show unprecedented high fluorescence quantum yields (Φf up to 69%, τf' 1-3 ns) and unexpectedly slow intersystem crossing for a series of rhodium complexes. This new class of compounds challenges our understanding of the behavior of excited electronic states and the role of the heavy atom in intersystem crossing processes. Mes = mesityl, THF = tetrahydrofuran, Tol = toluene. (Figure Presented).
