Theoretical study on photophysical property of cuprous bis-phenanthroline coordination complexes

The electronic structures and photophysical properties of phenathroline ligands coordinated to Cu(I), which are substituted in the 2,9-positions with methyl, phenyl, trifluoromethyl and tert-butyl groups, has been studied by density functional theory (DFT) and time-dependent DFT (TDDFT). To investigate the role played by counteranion in these complexes, the highest occupied orbital energies (HOMO), the lowest virtual orbital energies (LUMO), ΔH–L (the energies difference between the HOMO and LUMO), the lowest excitation energies (ES1), ionization potentials (IPs), electron affinities (EAs) and reorganization energies (λ) were computed. And through the study of the geometric relaxations, d-orbital splitting and spin-orbit couplings (SOC) at their optimized S0 and T1 geometries, non-radiative and radiative decay rate constants (knr and kr) were determined, for comparing and analyzing the different size and push/pull substituents effect on the luminescence quantum yield. Considering these factors, the dtbpdmp complex with tert-butyl group in the 2,9-positions has faster kr and singlet-triplet intersystem crossing (ISC) but slower knr, which leads to its higher photoluminescent quantum efficiency as compared to the methyl-, phenyl- and trifluoromethyl-based complexes.

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► The hole injection ability is improved with the presence of counteranion (PF6−).
► If the PF6− improves the hole injection ability greater, resulting in more imbalance.
► The hole transport rate is condition of the transport equilibrium property.