Gold(III) complexes supported by C-deprotonated fluorene-C^N^C ligands having high emission quantum yield up to 0.61 and long-lived emissive excited states are used as yellow emitters in color tunable PLEDs and OLEDs. High EQEs of 13.16% and 22.02% are achieved in the best PLED and OLED, respectively.

Long-lived, strongly emissive triplet excited states such as that of the Tb III complex of N 1 ,N 1' ,N 1'' ,N 1''' -(ethane-1,2-diylbis(azanetriyl))tetrakis(ethane-2,1-diyl)tetrakis(2-hydroxy-N 3methylisophthalamide) and Pd II porphyrins [1] can have profound impact in diverse areas including photocatalysis [2] and optical imaging. [3] Triplet excited states of transition-metal complexes with lifetimes of over hundreds of microseconds usually have little metal character as the latter facilitates radiative decay through a spin-orbit coupling mechanism. In this context, luminescent Au III complexes are promising systems as Au III ion usually contributes little to the emissive triplet excited states. As up to now, research on luminescent gold(III) complexes is in its infancy with the reported examples hardly showing emission quantum yields over 15 % in solutions at room temperature. [4, 5] Herein we show that incorporation of a fluorene moiety adjacent to a C donor atom of tridentate cyclometalated C^N^C ligands (Scheme 1) changes the lowest triplet excited state of the Au III complexes from intraligand charge transfer to ligandcentered p-p* one. Such a subtle structural modification gives rise to strongly luminescent Au III complexes with unprecedentedly high emission quantum yields of up to 58 % and excited state lifetimes over 200 ms in solutions at room temperature. These strongly emissive, long-lived excited states are instrumental to the observation and investigation of two-photon photophysical and photochemical properties of luminescent gold(III) systems.The structures of the gold(III) complexes 1 a-6 a are shown in Scheme 1. Details for their synthesis and characterization are given in the Supporting Information. X-ray crystal structures of 2 a and 6 a have been determined. [6] As shown in Figure 1, the Au atoms of both 2 a and 6 a adopt a distorted square-planar geometry with C-Au-C angles of 162.3(5)-162.5(1)8. The Au-C (C^N^C ligand) and Au-N distances are 2.058(3)-2.082(12) and 1.958(10) -2.005(2) , respectively, both of which are similar to those of other cyclometalated gold(III) complexes. Interestingly, the Au-C(acetylide) distance of 2 a is 1.915(11) , which is notably shorter than related reported Au-C(acetylide) distances. [4a,b, 5a] In dichloromethane solutions, complexes 1 a-5 a show intense absorption bands at 250-350 nm (e = 2-5 10 4 dm 3 mol À1 cm À1 ) and moderately intense absorption bands at 375-440 nm (e = 1-2 10 4 dm 3 mol À1 cm À1 ); 6 a exhibits intense absorption bands at 250-320 nm (e = 2 10 4 -1.2 10 5 dm 3 mol À1 cm À1 ) and 370-410 nm (e = 1-3 10 4 dm 3 mol À1 cm À1 ). These absorption bands are assigned to intraligand transitions localized on the C^N^C ligand.All of these gold(III) complexes having a C(fluorene)donor atom display vibronic structured emissions with peak maxima at 538-546 nm and vibrational spacings of about 1300 cm À1 in CH 2 Cl 2 at room temperature; these emissions are assigned to metal-perturbed intraligand transitions of the C^N^C ligand (Figure 2). Their ...

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