Hwang, Ah-Reum Han, Won-Sik Wee, Kyung-Ryang Kim, Hyun Young Cho, Dae Won Min, Byoung Koun Nam, Suk Woo Pac, Chyongjin Kang, Sang Ook 2024-01-20T15:33:12Z 2024-01-20T15:33:12Z 2021-09-04 2012-01-19 1932-7447 https://pubs.kist.re.kr/handle/201004/129635 We prepared dendrimers of heteroleptic iridium(III) complexes, [(dfppy-Cz(1))(2)Ir(dpq)](+) (G1) and [(dfppy-Cz(2))(2)Ir(dpq)](+). (G2), which have the dfppy ligand connected to carbazole-functionalized dendron Cz(n) (n = 1, 2) [dfppy-Cz(n) = 5-Cz(n)-2-(4,6-difluorophenyl)pyridine, dpq = 2,3-bis-(2-pyridyl)-qinoxaline, Cz(1) = 4-(9-carbazolyl)benzyloxymethyl, and Cz(2) = 4-[1,3-bis(9-carbazolyl)benzyloxy]benzyloxymethyl]. While parent complex [(dfppy)(2)Ir(dpq)](+) (G0) shows an intense emission at similar to 635 nm with a lifetime of 1 mu s assigned to dpq-based metal-to-ligand charge-transfer (MLCT) phosphorescence, excitation of the dendrimers at either carbazole (309 nm) or MLCT band (355 nm) resulted in markedly weaker and much shorter-lived MLCT emission (tau(p) = 44 ns for G1 and 115 ns for G2) at room temperature. Upon exciting the carbazole chromophore of G1 and G2 at 309 nm, furthermore, both the carbazole fluorescence and the MLCT emission were very weak at room temperature. It was found that the lifetime of carbazole fluorescence is 20 ps for G1 and 62 ps for G2, shorter by 2-orders of magnitude than that of free carbazole dendron Cz(n)'-OH (tau(p) = 6.1 ns). These observations demonstrate that both the excited-singlet state of carbazole and the triplet MLCT state of the Ir(dpq) core are efficiently quenched in the dendrimers. At 77K, however, the MLCT emission lifetime for both G1 and G2 is similar to 7 mu s that is nearly identical to that of G0 (6.8 mu s), and the carbazole fluorescence lifetime is similar to 11.5 +/- 0.5 ns, which is again almost the same as that of Cz(n)'-OH (11.5 ns). Since the apparent quenching of either carbazole fluorescence or MLCT emission observed at room temperature does not occur at 77 K, the temperature-dependent emission behavior of G1 and G2 for both the carbazole fluorescence and the MLCT phosphorescence was attributed to the participation of activated processes, that is, electron transfer from excited-singlet carbazole to the Ir(dpq) core as well as from the ground-state carbazole unit to the triplet MLCT Ir(dpq) core. This mechanism was supported by transient-absorption spectroscopic experiments that demonstrate the generation of the carbazole radical cation after exciting G1 and G2 by laser pulses. English American Chemical Society ORTHO-METALATED COMPLEXES LIGHT-EMITTING-DIODES MLCT EXCITED-STATES CYCLOMETALATED IRIDIUM(III) ELECTROCHEMICAL PROPERTIES DENDRITIC MACROMOLECULES PHOTOPHYSICAL PROPERTIES ABSORPTION-SPECTRA ENERGY-TRANSFER POLYPYRIDINE COMPLEXES Photodynamic Behavior of Heteroleptic Ir(III) Complexes with Carbazole-Functionalized Dendrons Associated with Efficient Electron Transfer Processes Article 10.1021/jp2093077 1 The Journal of Physical Chemistry C, v.116, no.2, pp.1973 - 1986 The Journal of Physical Chemistry C 116 2 1973 1986 scie scopus 000299584800041 2-s2.0-84862956677 Chemistry, Physical Nanoscience & Nanotechnology Materials Science, Multidisciplinary Chemistry Science & Technology - Other Topics Materials Science Article ORTHO-METALATED COMPLEXES LIGHT-EMITTING-DIODES MLCT EXCITED-STATES CYCLOMETALATED IRIDIUM(III) ELECTROCHEMICAL PROPERTIES DENDRITIC MACROMOLECULES PHOTOPHYSICAL PROPERTIES ABSORPTION-SPECTRA ENERGY-TRANSFER POLYPYRIDINE COMPLEXES Dendrons Electron transfer