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DOI: 10.1039/C8CC01652F
COMMUNICATION
Journal Name
(63 oC), the elongation enthalpy (He) was t46.9 kJ molt1, the There are no conflicts to declare.
number-averaged degree of polymerization at Te (<Nn(Te)>) was
11, and the equilibrium constant of the activation step at the Notes and references
elongation temperature (Ka) is 7.9ì
10t4 Mt1. The
supramolecular polymerization of complex 1c in toluene takes
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a
elongates the aggregates of 1c into polymers.
0.20
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lLCT/MLCT
MMLCT
0.15
Pd∂∂∂Pd
3.164 Å
0.10
0.05
Dimer
Monomer
0.00
200
300
400
500
600
700
l / nm
Fig. 5
TD-DFT calculated UV-Vis absorption spectra of monomeric and dimeric Pd(II)
NHA cation(s) with toluene as solvent. Inset shows the molecular orbitals involved in the
lower-energy transitions at the optimized geometry.
We performed time-dependent density functional theory
calculations on the monomeric and dimeric structures of the
Pd(II) NHA cations in toluene, using B3LYP-D3 functional (B3LYP
with dispersion correction) with basis set of 6-31G(d) for C, H,
O, and N atoms and LanL2DZ basis set for the Pd atom (see ESI
for details). The lowest-energy transition in the calculated
absorption spectrum (Fig. 5) of the monomer at 415 nm
(oscillation strength 0.003) involves intraligand charge-transfer
(ILCT) on the (C^N^N) ligand and Pd(4dz2) to NHA metal-to-
ligand charge transfer (MLCT). In contrast, the calculated
lowest-energy transition of the dimeric structure with a close
Pd∂∂∂Pd contact (optimized to be 3.164 Å) is at 489 nm
(oscillation strength 0.047), which originates from an electronic
transition from the antibonding d•Ž~ðꢃÌ2) orbital to the weakly
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stacked (C^N^N) ligand
p* orbital. The calculated and
experimental absorption spectra converged to provide
compelling evidences for the MMLCT excited state of Pd(II) NHA
in aggregated species.
In summary, tridentate cyclometalated Pd(II) allenylidene
complexes exhibit highly emissive and sensitive MMLCT excited
states in the solid state and as aggregates in solutions. We
envisage that the MMLCT photochemistry of Pd(II) could be as
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This work was supported by National Natural Science
Foundation of China (21571096) and Science and Technology
Innovation Commission of Shenzhen Municipality (JCYJ
20160301114634613 and JCYJ20170817104715174).
Conflicts of interest
4 | J. Name., 2012, 00, 1-3
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