Circularly Polarized Luminescence of Chiral Pt(pppb)Cl (pppbH=1‐pyridyl‐3‐(4,5‐pinenopyridyl)benzene) Aggregate in the Excited State

Abstract

We prepared enantiomers of chiral Pt(II) complexes, Pt(pppb)Cl and Pt(pppb)CN (pppbH=1-pyridyl-3-(4,5-pinenopyridyl)benzene), and measured their CPL (circularly polarized luminescence) spectra for excimer and trimer emission. The contribution of the pinene moiety to CPL was considerably low for the π-π* emission of the monomer but large for MMLCT (metal-metal-to-ligand charge-transfer) of the excimer and trimer which had a helical structure induced in a face-to-face stacking fashion. The trimer CPL for (+)-Pt(pppb)Cl was larger in intensity than that of excimer CPL; on the other hand, that for (+)-Pt(pppb)CN was opposite in sign compared with that of excimer CPL. We conclude that differences in the excited-state structure of the aggregate between Pt(pppb)Cl and Pt(pppb)CN account for the variation in the CPL spectra. By the aid of TD-DFT calculations it was predicted that the dihedral angle θ(Cl-Pt-Pt-Cl) was 50-60° or 110-140° for Pt(pppb)Cl aggregates and 160° for Pt(pppb)CN aggregates.

Recent Progress on Circularly Polarized Luminescent Materials for Organic Optoelectronic Devices

“…However, there were no such phenomenon observed for 59‐P/M and 60‐P/M . Similarly, the behavior of self‐assemblies to form stacked aggregates via Pt–Pt, π–π stacking, and dipole–dipole interactions is another effective method to enhance the dissymmetry g lum factors . For example, two novel enantiomers of Pt(II) phenylbipyridine complexes ( 61‐R/S ) with bis(phenylisoxazolyl)phenylacetylene ligands which were linked with a chiral alkyl chains were designed and synthesized .…”

Pt⋯Pt interaction triggered tuning of circularly polarized luminescence activity in chiral dinuclear platinum(ii) complexes

“…Meanwhile, the g lum values are similar to those of the reported cases for helicene derived Pt(II) complexes or square-planar Pt(II) complexes with helical structures. [10][11][12][13][14][15][16][17] Due to the short distance and interactions between the two platinum centers, the CPL bands of complex (−)-1 are dominated by the dimeric excited state 3 MMLCT. For complex (−)-2, the CPL bands mainly come from monomeric excited state 3 MLCT.…”

“…4 In recent years, due to high emission quantum efficiency and tunable excited-state properties, growing attention has been paid to the development of new CPL-active materials focusing on phosphorescent transition metal complexes, such as Ir, Zn, Pt and so on. [5][6][7][8][9][10][11][12][13][14][15][16][17] Among the phosphorescent materials based on transition metal complexes, square-planar Pt(II) complexes are capable of forming self-assemblies, resulting in intriguing luminescent and conductive properties. 18,19 When a chiral substituent is incorporated, the packing of adjacent units adopts a staggered pattern alongside the Pt⋯Pt chain due to steric hindrance, which is favourable for forming a helical supramolecular structure.…”

“…The helical structure may exhibit a significant difference in the magnetic dipole transition from the excited triplet state to the ground state, which can show interesting CPL activity. [14][15][16][17] Through incorporation of a helical fragment or heterobidentate trans-spanning blocks, distinctive CPL signals can also be accessed in Pt(II) complexes, [10][11][12] some of which have been exploited to fabricate circularly polarized phosphorescent organic light-emitting diodes (CP-PHOLEDs) with a good brightness and a sizable dissymmetry factor (g lum , defined as: g lum = 2(I L − I R )/(I L + I R ) where I L and I R are the leftand right-circularly polarized intensity, respectively). 13 Recently, studies on vapor-, solvent-, mechano-, and temperature-induced structural and chiroptical switches of cyclometalated Pt(II) complexes 17,20 indicated that CPL activity can be reasonably tuned by the manipulation of temperature and solvent.…”

Solvent-tuned charge-transfer properties of chiral Pt(ii) complex and TCNQ˙− anion adducts

“…24 Additionally, helical assemblies of Pt(II) complexes can be formed in solution with the introduction of optically pure groups, correspondingly leading to interesting on-off switching of chiral signals. [25][26][27][28][29][30] It is suggested that these abovementioned stimuli-induced switches can be harnessed to develop versatile sensors to detect subtle environmental changes. [31][32][33][34] 7,7,8,8-Tetracyanoquinodimethane (TCNQ) has been widely investigated as a good electron acceptor due to its high electron affinity.…”