Electronic Structure Studies and Photophysics of Luminescent Th(IV) Anilido and Imido Complexes

Abstract

A series of thorium anilide compounds [ThNHAr R (TriNOx)] (R = para-OCH 3 (1-Ar OMe ), para-H (1-Ar H ), para-Cl (1-Ar Cl ), para-CF 3 (1-Ar 4-CF3 ), TriNOx 3− = tris(2-tert-butylhydroxylaminato)benzylamine), and their corresponding imido compounds [Li(DME)][Th�NAr R (TriNOx)] (2-Ar R ) as well as the alkyl congeners [ThNHAd(TriNOx)] (1-Ad) and [Li(DME)][Th�NAd(TriNOx)] (2-Ad), have been prepared. The para-substituents on the arylimido moiety were introduced for systematic variation of their electron-donating and withdrawing abilities, changes that were evident in measurements of the 13 C{ 1 H} NMR chemical shifts of the ipso-C atom of the Ar R moiety. Room temperature, solution-state luminescence of the four new thorium imido compounds, along with the previously reported [Li(THF) 2 ][Th�NAr 3,5-CF3 (TriNOx)] (2-Ar 3,5-CF3 ) and [Li(THF)(Et 2 O)]-[Ce�NAr 3,5-CF3 (TriNOx)] (3-Ar 3,5-CF3) have been described. Among these complexes, 2-Ar 3,5-CF3 demonstrated the most intense luminescence feature with excitation at 398 nm and emission at 453 nm. The luminescence measurements, together with a timedependent density functional theory (TD-DFT) study, helped uncover an intra-ligand n → π* transition that was assigned as the origin of the bright blue luminescence; 3-Ar 3,5-CF3 has an 1.2 eV redshift in excitation energy compared with its proligand. The weak luminescence of other derivatives (2-Ar R and 3-Ar 3,5-CF3 ) was attributed to non-radiative decay from low-lying excited states originating from inter-ligand transitions (2-Ar R ) or ligand-to-metal charge transfer bands (3-Ar 3,5-CF3 ). Overall, the results expand the range of the thorium imido organometallic compounds and demonstrate that thorium(IV) complexes can support strong ligand luminescence. The results also demonstrate the utility of applying a Th(IV) center for tuning the n → π* luminescence energy and intensity of an associated imido moiety.

Synthesis and Luminescence Studies of a Tethered, Trigonal, Silver(I) Tris(alkyne) Complex

“…The reduced Stokes shift observed for 1-Ag suggests that coordination of 1 to the Ag + inhibits nonradiative vibrational relaxation processes. The similarities between the excitation and emission spectra of 1 and 1-Ag and the energies of the transitions indicate that the luminescent behavior of both species originates from intraligand π–π* transitions, a phenomenon observed in the literature for other aryl organometallic complexes …”

“…The similarities between the excitation and emission spectra of 1 and 1-Ag and the energies of the transitions indicate that the luminescent behavior of both species originates from intraligand π−π* transitions, a phenomenon observed in the literature for other aryl organometallic complexes. 44 Fluorescence lifetime measurements were obtained for 1 and 1-Ag at 360 nm excitation (Figures S29 and S30). Optimized multiexponential fits obtained for 1 and 1-Ag yielded two decay processes for each compound.…”

Synthesis and Characterization of Isostructural Th(IV) and U(IV) Pyridine Dipyrrolide Complexes

“…This value indicates a high quantum efficiency for complex 2b and is substantially larger than values reported previously for Th(IV) complexes (e.g., [Li(THF) 2 ][Th = NAr 3,5-CF3 (TriNOx)]; QY = 2.5%). 79 The photoluminescence decay for Th( Mes PDP Ph ) 2 revealed a lifetime of 304 μs, which we hypothesize to be due to the decay of a long-lived triplet excited state ( Figure S14 ). 85…”