Upconverted Emission from Pyrene and Di-tert-butylpyrene Using Ir(ppy)₃ as Triplet Sensitizer

Abstract

Metal-to-ligand charge-transfer sensitized upconverted fluorescence in noncovalent triplet energy transfer assemblies is investigated using Ir(ppy)3 as the sensitizer (ppy=2-phenylpyridine) and pyrene or 3,8-di-tert-butylpyrene as the triplet acceptor/annihilator. Upconverted singlet fluorescence from pyrene or 3,8-di-tert-butylpyrene resulting from triplet-triplet annihilation (TTA) is observed following selective excitation of Ir(ppy)3 in deaerated dichloromethane solutions using 450-nm laser pulses. In both systems, the TTA process is confirmed by the near quadratic dependence of the upconverted fluorescence intensity on incident light power, measured by integrating the upconverted delayed fluorescence kinetic traces as a function of incident excitation power. At the relatively high concentrations of pyrene that were utilized, pyrene excimer formation was detected by its characteristic broad emission centered near 470 nm. In essence, selective excitation of Ir(ppy)3 ultimately resulted in the simultaneous sensitization of both singlet pyrene and pyrene excimers, and the latter degrades the energy stored in the pyrene singlet excited state. Furthermore, in the case of di-tert-butylpyrene/Ir(ppy)3, the formation of excimers is successfully blocked because of the presence of the sterically hindering tert-butyl groups. The current work demonstrates that sensitized TTA is indeed accessible to chromophore systems beyond those previously reported, suggesting the generality of the approach.

Visible‐Light Harvesting with Cyclometalated Iridium(III) Complexes Having Long‐Lived 3IL Excited States and Their Application in Triplet–Triplet‐Annihilation Based Upconversion

“…We noted that a cyclometalated Ir III complex, Ir(ppy) 3 (ppy = 2-phenylpyridine, τ = 2.0 μs), [1] has been used for TTA upconversion. [37] However, without the lightharvesting effect, the absorption maximum of that complex is centered at 390 nm, and molar extinction coefficients are much smaller than those of Ir-3 and Ir-4.…”

Upconversion with ultrabroad excitation band: Simultaneous use of two sensitizers

“…The first one in the chain is intersystem crossing at the sensitizer 1 molecules which is followed by the second process-transfer of the excitation of the sensitizer triplet to the emitter triplet. Recently, it has been shown that metallated macrocycles ͑MMs͒ such as platinum-, palladium-, zinc, and copper octaethylporphyrins 4,5 as well as Ru͑II͒ diimineand iridium phenylpyridine-metal-to-ligand charge transfer complexes 6,7 can serve as sensitizers in the bimolecular upconversion processes. 3 An efficient triplet-triplet annihilation assisted photon upconversion has been observed for a broad variety of metal complexes, acting as sensitizers, and different emitter molecules.…”

Enabling a bright orange–red emission with a high EQE with a seven-member-ring based fluorescent emitter with a matching host

“…6(a) and (b), may be attributed to the increasing excitons generated on the host molecules as well as those on the guest counterparts at elevated bias, as reported in the literature [13]. Although it is not uncommon for fluorescent OLEDs to exceed the 5% theoretical EQE limit, and several mechanisms, such as triplet-triplet-annihilation (TTA) [16] and thermally activated delayed fluorescence [28,29] had been proposed, it still is surprising to see the orange-red OLED to exhibit a record high EQE of 7.2% at such a high brightness, namely 25,000 cd/m 2 . The reasons why the resultant EQE of the BANE host based device showed an unprecedented roll-up phenomena may be attributed to following mechanisms.…”

“…Especially in the last case, the major emission was contributed by the host of Ir(ppy) 3 , and emission from the red dye was not at all observable. This reveals that the electrophosphorescence-based Ir(ppy) 3 cannot function as a host for the fluorescent red dye studied, although other studies have proven that it can act as an effective cohost or sensitizer in other dye systems [28,29].…”