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Theoretical Insights into the Phosphorescence Quantum Yields of Cyclometalated (C∧C*) Platinum(II) NHC Complexes: π‑Conjugation Controls the Radiative and Nonradiative Decay Processes
journal contribution
posted on 2016-01-25, 00:00 authored by Yafei Luo, Yanyan Xu, Wenting Zhang, Wenqian Li, Ming Li, Rongxing He, Wei ShenIn
this article, the radiative and nonradiative decay processes
of four cyclometalated (C∧C*) platinum(II) N-heterocyclic
carbene (NHC) complexes were unveiled via density functional theory
and time-dependent density functional theory. In order to explore
the influence of π-conjugation on quantum yields of (NHC)Pt(acac)
(NHCN-heterocyclic carbene, acac = acetylacetonate) complexes,
the factors that determine the radiative process, including singlet–triplet
splitting energies, transition dipole moments, and spin–orbit
coupling (SOC) matrix elements between the lowest triplet states and
singlet excited states were calculated. In addition, the SOC matrix
elements between the lowest triplet state and the ground state as
well as Huang–Rhys factors were also computed to describe the
temperature-independent nonradiative decay processes. Also, the triplet
potential energy surfaces were investigated to elucidate the temperature-dependent
nonradiative decay processes. The results indicate that complex Pt-1 has higher radiative decay rate than complexes Pt-2–4 due to the larger SOC matrix elements between
the lowest triplet states and singlet excited states. However, complexes Pt-2–4 have smaller Huang–Rhys factors, smaller
SOC matrix elements between the lowest triplet and the ground states,
and higher active energy barriers than complex Pt-1,
indicating that complexes Pt-2–4 have smaller
nonradiative decay rate constants. According to these results, one
may discern why complex Pt-2 has higher phosphorescence
quantum efficiency than complex Pt-1; meanwhile, it can
be inferred that the nonradiative decay process plays an important
role in the whole photodeactivation process. In addition, on the basis
of complex Pt-2, Pt-5 was designed to investigate
the influence of substitution group on the photodeactivation process
of rigid (NHC)Pt(acac) complex.