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Excited-State Switching between Ligand-Centered and Charge Transfer Modulated by Metal–Carbon Bonds in Cyclopentadienyl Iridium Complexes

Journal Article · · Inorganic Chemistry
 [1];  [2];  [3];  [4];  [2];  [3];  [2]
  1. North Carolina State Univ., Raleigh, NC (United States); NC State University
  2. North Carolina State Univ., Raleigh, NC (United States)
  3. Univ. of North Carolina, Chapel Hill, NC (United States)
  4. Univ. of Regensburg (Germany)
+ Show Author Affiliations
Three series of pentamethylcyclopentadienyl (Cp*) Ir(III) complexes with different bidentate ligands were synthesized and structurally characterized, [Cp*Ir(tpy)L]n+ (tpy = 2-tolylpyridinato; n = 0 or 1), [Cp*Ir(piq)L]n+ (piq = 1-phenylisoquinolinato; n = 0 or 1), and [Cp*Ir(bpy)L]m+ (bpy = 2,2'-bipyridine; m = 1 or 2), featuring a range of monodentate carbon-donor ligands within each series [L = 2,6-dimethylphenylisocyanide; 3,5-dimethylimidazol-2-ylidene (NHC); methyl)]. The spectroscopic and photophysical properties of these molecules and those of the photocatalyst [Cp*Ir(bpy)H]+ were investigated to establish electronic structure–photophysical property relationships that engender productive photochemical reactivity of this hydride and its methyl analogue. The Ir(III) chromophores containing ancillary CNAr ligands exhibited features anticipated for predominantly ligand-centered (LC) excited states, and analogues bearing the NHC ancillary exhibited properties consistent with LC excited states containing a small admixture of metal-to-ligand charge-transfer (MLCT) character. Yet, the molecules featuring anionic and strongly σ-donating methyl or hydride ligands exhibited photophysical properties consistent with a high degree of CT character. Density functional theory calculations suggest that the lowest energy triplet states in these complexes are composed of a mixture of MLCT and ligand-to-ligand CT originating from both the Cp* and methyl or hydride ancillary ligands. The high degree of CT character in the triplet excited states of methyliridium complexes bearing C^N-cyclometalated ligands offer a striking contrast to the photophysical properties of pseudo-octahedral structures fac-Ir(C^N)3 or Ir(C^N)2(acac) that have lowest-energy triplet excited states characterized as primarily LC character with a more moderate MLCT admixture.
Research Organization:
North Carolina State Univ., Raleigh, NC (United States); Univ. of North Carolina, Chapel Hill, NC (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Grant/Contract Number:
SC0011979; SC0014255
OSTI ID:
1633629
Journal Information:
Inorganic Chemistry, Journal Name: Inorganic Chemistry Journal Issue: 24 Vol. 57; ISSN 0020-1669
Publisher:
American Chemical Society (ACS)Copyright Statement
Country of Publication:
United States
Language:
English

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Cited By (1)

Efficient blue, green and red iridium( iii ) complexes with noncovalently-linked pyrazole/pyrazolide rings for organic light-emitting diodes journal January 2020

Figures / Tables (14)

Scheme 1(p. 2)figure Scheme 1
Scheme 2(p. 3)figure Scheme 2
Table 1(p. 3)table Table 1
Figure 1(p. 4)figure Figure 1
Figure 2(p. 5)figure Figure 2
Figure 3(p. 5)figure Figure 3
Table 2(p. 6)table Table 2
Figure 4(p. 7)figure Figure 4
Figure 5(p. 7)figure Figure 5
Figure 6(p. 9)figure Figure 6
Figure 7(p. 9)figure Figure 7
Figure 8(p. 10)figure Figure 8
Table 3(p. 10)table Table 3
Table 4(p. 10)table Table 4

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