Quantum-Chemical Insights into the Phosphorescence Efficiencies of Blue-Emitting Platinum Complexes with Phenylene-Bridged Pincer Ligands

Abstract

Blue phosphorescent platinum complexes with phenylene-bridged pincer ligands, [Pt(dmib)Cl] [1; dmib = m-bis(methylimidazolyl)benzene], [Pt(mizb)Cl] [2; mizb = bis(N-methylimidazolium)benzene], and [Pt(dpzb)Cl] [3; dpzb = m-bis( 3,5-dimethylpyrazolyl)benzene], have been investigated theoretically to rationalize the marked differences of their phosphorescence efficiencies. On the basis of density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations, the geometrical and electronic structures, absorption and emission properties, and radiative and nonradiative processes are analyzed in detail. The emission from the emissive lowest triplet state (T 1 ) originates from a mixture of metal-to-ligand charge-transfer ( 3 MLCT) and intraligand charge-transfer ( 3 ILCT) states. The calculated radiative decay rate constants of T 1 of the complexes are comparable and in the same order of magnitude with the experimental measurements. Therefore, the potential energy profiles for the deactivation processes from T 1 via temperature-independent and -dependent pathways are explored to reveal the effect of nonradiative decay on phosphorescence. The calculated results indicate that the very weak emission of 3 could be ascribed to the deactivation process via the metal-centered ( 3 MC) state, which can be readily accessible via a spontaneous process from the T 1 state. This work provides more in-depth insight into the nature of the emissive excited state, shielding light on a better understanding of the excited-state behavior of phosphorescent platinum complexes.

Behind the scenes of spin-forbidden decay pathways in transition metal complexes

“…Also, the thermal stability and charge neutrality of cyclometallated Pt(II) complexes render them good candidates as triplet emitters. 143,144 The triplet state population rates of Pt(II) complexes are moderate and thus structure or environment alterations can swing the balance towards purely phosphorescent or dual emissive luminescence behavior.…”

Luminescent PtII and PtIV Platinacycles with Anticancer Activity Against Multiplatinum‐Resistant Metastatic CRC and CRPC Cell Models

“…The lowest energy bands in the 357–386 nm range can be attributed to Pt(5d)→π* metal‐to‐ligand charge transfer (MLCT) mixed with intraligand transitions. An additional high energy absorption band, observed in the range 275–301 nm with higher ϵ values, can be attributed to π→π* intraligand transitions, as it matches the absorption recorded for the free ligand (Figure S9, Supporting Information) . Pt IV compounds only show absorption bands in the high energy range, except for compound 3 b′ which also displays lower energy absorption bands.…”

“…2a' [17] 277 (7524) Pt II cyclometallated compounds show severala bsorption bands in the UV/Visible range ( Figure S8, Supporting Information). [18][19][20] Pt IV compoundso nly show absorption bands in the high energy range, except for compound 3b' which also displays lower energy absorptionbands. An additional high energy absorption band, observed in the range 275-301 nm with higher e values, can be attributed to p!p*i ntraligand transitions, as it matches the absorption recorded for the free ligand ( Figure S9, Supporting Information).…”

“…An additional high energy absorption band, observed in the range 275-301 nm with higher e values, can be attributed to p!p*i ntraligand transitions, as it matches the absorption recorded for the free ligand ( Figure S9, Supporting Information). [18][19][20] Pt IV compoundso nly show absorption bands in the high energy range, except for compound 3b' which also displays lower energy absorptionbands.…”

Revealing the marked differences of phosphorescence efficiencies on C˄N˄N‐coordinated Pt(II) complexes: A theoretical study

“…The ground and excited geometries were optimized by using hybrid functional PBE0 [12,13] and unrestricted PBE0 functional, respectively, which had been stably and credibly implemented in the calculation of Pt complexes. [14,15] The 6-31G(d,p) basis set and the LANL2DZ basis set [16,17] were applied to nonmetal atoms and heavy Pt atoms, respectively. Vibrational frequencies were calculated at the same level to ensure that the optimized structures were minimums on the potential energy surface.…”