Design, Synthesis, and Optoelectronic Properties of Dendrimeric Pt(II) Complexes and Their Ability to Inhibit Intermolecular Interaction

Abstract

Dendrimeric Pt(II) complexes [(C(∧)N)Pt(dpm)] and [Pt(C(∧)N)2] (Hdpm = dipivaloylmethane, HC(∧)N = 1,2-diphenylbenzoimidazole and its derivatives containing the carbazole dendrons) have been synthesized and characterized systematically. All of the complexes display green emission in the range of 495-535 nm that originated from the 360-440 nm absorption bands, which are assigned to dπ(Pt)→π*(L) metal-to-ligand charge transfer (MLCT) mixed with intraligand π(L)→π*(L) transition. Solution photoluminescence quantum yield (φp 0.26-0.31) of the heteroleptic complexes [(C(∧)N)Pt(dpm)] obviously increases when compared with that of complex [(C(∧)N)Pt(acac)]. Organic light-emitting diode devices based on these Pt(II) complexes with a multilayer configuration were fabricated and gave desirable electroluminescent (EL) performances, such as non- or less red-shifted EL spectra, in comparison with the photoluminescence spectra and slow efficiency roll-off with increasing brightness or current density. Complex [(t-BuCzCzPBI)Pt(dpm)] (where t-BuCzCzPBI = 1-(4-(3,6-di-(3,6-di-t-butyl-carbazol-9-yl))carbazol-9-yl)phenyl-2-phenylbenzoimidazole) showed the best performance, with a maximum current efficiency of 29.31 cd/A and a maximum external quantum efficiency (EQE) of 9.04% among the fabricated devices. Likewise, for homoleptic [Pt(t-BuCzCzPBI)2] dendrimer, the powder φp (0.14) and maximum EQE (0.74%) improve by 7 and 7.4 times, respectively, as high as they do for nondendrimeric [Pt(1,2-diphenylbenzoimidazole)2] (0.02, 0.10%), although its efficiency is still lower than that of the heteroleptic counterpart due to the severely distorted square-planar geometry of the emitting core. These results reveal that large steric hindrance from ancillary ligand (dpm) or the homoleptic conformation can effectively inhibit intermolecular interaction for these dendrimeric Pt(II) complexes.

Heteroleptic Cycloplatinated N-Heterocyclic Carbene Complexes: A New Approach to Highly Efficient Blue-Light Emitters

“…Most of the works on Pt based OLEDs deals with devices fabricated with vacuum evaporation techniques [37][38][39] due to the low solubility and/or poor ability of these compounds to form thin homogeneous films when deposited from solution. To the best of our knowledge, solution processed devices so far reported have been obtained with emissive layer (EML) composed by host-guest systems where the Pt emitter is blended in either polymeric or molecular hosts in order to reduce aggregation quenching processes and to increase the film homogeneity, both for molecular [40][41][42][43][44] and 20 dendrimeric emitters. 45,46 For these reasons all the devices so far reported with non-doped EML have been obtained by using vacuum processed technologies.…”

Ultrafast Excited-State Dynamics of Diketopyrrolopyrrole (DPP)-Based Materials: Static versus Diffusion-Controlled Electron Transfer Process

“…7,8 In particular, recently, a square-planar coordination of Pt(II) complexes have attracted great interest for their optical properties, which enable effective intersystem crossing (ISC) to the triplet state for many potential applications. [9][10][11][12][13][14][15][16][17] The photophysical properties of Pt(II) complexes strongly depend on the chemical structures of the cyclometalated ligands, where the emission energies of the complexes are related to the planarity and π-conjugation of the chromophoric ligands. 18 Pt(II) complexes bearing π-conjugated polymers and oligomers are established as promising for use in organic photovoltaic (OPV) applications due to their efficient light harvesting, structural versatility, and intrinsic charge-transport behavior.…”

Synthesis, characterization and solid-state photoluminescence studies of six alkoxy phenylene ethynylene dinuclear palladium(ii) rods

“…[41][42][43][44][45][46][47][48] The luminescence properties of organometallic compounds in solution are well-documented. [9][10][11][49][50][51][52][53][54][55][56][57][58][59] The inclusion of transition metal moieties gives access to efficient spin-orbit coupling, which, in turn, enables the population of excited states of triplet character and phosphorescence characteristics of organometallic compounds. As such the coordination of the organic compounds to metal centers can enrich the emission properties by enabling access to new excited-state species.…”