Unravelling the Mechanism of Excited-State Interligand Energy Transfer and the Engineering of Dual Emission in [Ir(C ∧ N) 2 (N ∧ N)] + Complexes
Fundamental insights into the mechanism of triplet-excited-state interligand energy transfer dynamics and the origin of dual emission for phosphorescent iridium(III) complexes are presented. The complexes [Ir(C N) (N N)] (HC N = 2-phenylpyridine ( - ), 2-(2,4-difluorophenyl)pyridine ( - ), 1-benzyl-...
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| Vydané v: | Inorganic chemistry Ročník 59; číslo 3; s. 1785 |
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| Hlavní autori: | , , , , , , , , , , , |
| Médium: | Journal Article |
| Jazyk: | English |
| Vydavateľské údaje: |
United States
03.02.2020
|
| ISSN: | 1520-510X |
| On-line prístup: | Zistit podrobnosti o prístupe |
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| Shrnutí: | Fundamental insights into the mechanism of triplet-excited-state interligand energy transfer dynamics and the origin of dual emission for phosphorescent iridium(III) complexes are presented. The complexes [Ir(C
N)
(N
N)]
(HC
N = 2-phenylpyridine (
-
), 2-(2,4-difluorophenyl)pyridine (
-
), 1-benzyl-4-phenyl-1,2,3-triazole (
-
); N
N = 1-benzyl-4-(pyrid-2-yl)-1,2,3-triazole (pytz,
), 1-benzyl-4-(pyrimidin-2-yl)-1,2,3-triazole (pymtz,
), 1-benzyl-4-(pyrazin-2-yl)-1,2,3-triazole (pyztz,
)) are phosphorescent in room-temperature fluid solutions from triplet metal-to-ligand charge transfer (
MLCT) states admixed with either ligand-centered (
LC) (
,
, and
) or ligand-to-ligand charge transfer (
LL'CT) character (
,
, and
-
). Particularly striking is the observation that pyrimidine-based complex
exhibits dual emission from both
MLCT/
LC and
MLCT/
LL'CT states. At 77 K, the
MLCT/
LL'CT component is lost from the photoluminescence spectra of
, with emission exclusively arising from its
MLCT/
LC state, while for
switching from
MLCT/
LL'CT- to
MLCT/
LC-based emission is observed. Femtosecond transient absorption data reveal distinct spectral signatures characteristic of the population of
MLCT/
LC states for
,
, and
which persist throughout the 3 ns time frame of the experiment. These
MLCT/
LC state signatures are apparent in the transient absorption spectra for
and
immediately following photoexcitation but rapidly evolve to yield spectral profiles characteristic of their
MLCT/
LL'CT states. Transient data for
reveals intermediate behavior: the spectral features of the initially populated
MLCT/
LC state also undergo rapid evolution, although to a lesser extent than that observed for
and
, behavior assigned to the equilibration of the
MLCT/
LC and
MLCT/
LL'CT states. Density functional theory (DFT) calculations enabled minima to be optimized for both
MLCT/
LC and
MLCT/
LL'CT states of
-
and
-
. Indeed, two distinct
MLCT/
LC minima were optimized for
,
,
, and
distinguished by upon which of the two C
N ligands the excited electron resides. The
MLCT/
LC and
MLCT/
LL'CT states for
are very close in energy, in excellent agreement with experimental data demonstrating dual emission. Calculated vibrationally resolved emission spectra (VRES) for the complexes are in excellent agreement with experimental data, with the overlay of spectral maxima arising from emission from the
MLCT/
LC and
MLCT/
LL'CT states of
convincingly reproducing the observed experimental spectral features. Analysis of the optimized excited-state geometries enable the key structural differences between the
MLCT/
LC and
MLCT/
LL'CT states of the complexes to be identified and quantified. The calculation of interconversion pathways between triplet excited states provides for the first time a through-space mechanism for a photoinduced interligand energy transfer process. Furthermore, examination of structural changes between the possible emitting triplet excited states reveals the key bond vibrations that mediate energy transfer between these states. This work therefore provides for the first time detailed mechanistic insights into the fundamental photophysical processes of this important class of complexes. |
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| ISSN: | 1520-510X |
| DOI: | 10.1021/acs.inorgchem.9b03003 |