Enhancement of Chiroptical Responses of trans‐Bis[(β‐iminomethyl)naphthoxy]platinum(II) Complexes with Distorted Square Planar Coordination Geometry

Abstract

The relationship between the coordination geometry and photophysical properties of trans ‐bis[(β‐iminomethyl)naphthoxy]platinum(II) was investigated both experimentally and theoretically. A series of platinum(II) complexes with differently substituted iminomethyl groups were synthesized, and their photophysical properties were examined in solution, in the crystalline, and in the PMMA film‐dispersed state, respectively (PMMA=poly(methyl methacrylate)). These complexes showed structure‐dependent emission spectra, in which the color of the luminescence in the crystalline state varied over a range of about 40 nm depending on the specific bowl‐shaped molecular structure. The chiral complexes with ( R,R )‐ and ( S , S )‐configurations were found to have structure‐dependent chiroptical properties both in solution and the PMMA film‐dispersed state such that the intensity of circular dichroism (CD) and circularly polarized luminescence (CPL) were enhanced with bulky cyclic substituents at the nitrogen atoms. A theoretical study using density functional theory (DFT) and time‐dependent (TD)‐DFT calculations revealed that the enhancement of chiroptical responses is due to the amplification of the magnetic dipole moment caused by the distortion of the square planar geometry.

Circularly polarized luminescence of pinene-modified tetradentate platinum(II) enantiomers containing fused 5/6/6 metallocycles

“…Complexes (−)- 1 and (+)- 1 show symmetrically appreciable CPL signals at 480–620 nm with the g lum factors on the order of 10 −3 (+1.05 × 10 −3 for (−)- 1 and -0.93 × 10 −3 for (+)- 1 at 530 nm) ( Figure 7 ). The dissymmetric factor is comparable to the CPL signals for the reported phosphorescent CPL-active Pt(II) complexes with helicene, axial chirality, helical chirality, and chiral-at-metal [ 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 ].…”

“…In addition to the above two strategies, another method to obtain CPL-active Pt(II) complexes is to utilize coordination chirality [ 20 , 21 , 22 , 23 ]. Through choosing appropriate chelating ligands such as trans -spanning phenylpyridine, substituted (2-thienyl)pyridine and trans -bis[( β -iminomethyl)aryloxy], chiral-at-metal, chiral-at-plane and chiral-at-cluster Pt(II) complexes with significant CPL response and distinct anisotropic factors g lum ( g lum = 2Δ I / I = 2( I L – I R )/( I L + I R ), where I L and I R refer, respectively, to the intensity of circularly polarized emissions of left and right) could be successfully induced [ 24 , 25 , 26 , 27 , 28 , 29 ]. When these twisted Pt(II) complexes serve as chiral emitters, low-cost CP-PhOLEDs could be fabricated through a solution process, achieving competitive luminance efficiency, external quantum efficiency, and asymmetry factor [ 30 , 31 ].…”

Circularly Polarized Luminescence of Cyclometalated Platinum(II) Complex Excimers: Large Difference between Isomers

“…Many papers studying the CPL spectra of organic and inorganic materials have been published from many laboratories. , Aggregation-induced luminescence and CPL have recently attracted considerable attention in the field of organic and coordination chemistry. − A large enhancement of the CPL signal in polymer materials has also been reported. , Especially, many papers studying CPL of platinum­(II) complexes have been published in recent years. − They also include enhancement of CPL signals via aggregation-related phenomena − and device-oriented works. ,− However, few studies have been carried out to evaluate the CPL of excimers or exciplexes . Recently, to the best of our knowledge, only one study has reported the enhancement of the intensity of the CPL signal due to chiral excimer formation based on platinum­(II) complexes in solution.…”

Circularly polarized phosphorescence with a large dissymmetry factor from a helical platinum(ii) complex

“…1–3 Square planar platinum( ii ) complexes are widely known for their highly efficient phosphorescent emission, and CPP materials have been created by introducing chiral ligands. 4–17 Several chiral platinum( ii ) complexes have been reported to show CPP with large dissymmetry factors ( g lum = 2Δ I / I = 2( I L − I R )/( I L + I R )) 18 in the aggregated state. 7,8,12,16 In particular, the co-assembly of achiral and chiral platinum complexes reported by You and coworkers showed a considerably large g lum value of 0.064 from a magnetically-allowed metal–metal-to-ligand charge transfer (MMLCT) transition.…”

“…Our research group has been investigating the photophysical properties of chiral transition metal complexes and recently found that Schiff-base platinum( ii ) complexes with a distorted square planar coordination platform exhibit tunable CPP properties in solution, 11,13,14 in the polymer-dispersed state, 10 and in the solvent-free liquid state. 12 In the present study, we designed a novel chiral platinum complex 1 with a Schiff-base [4]helicene ligand and the photophysical properties of the complex were compared with its analogue 2 (Scheme 1).…”