Homoleptic Alkynylphosphonium Au(I) Complexes as Push–Pull Phosphorescent Emitters

Abstract

A series of compounds P1–P4 bearing terminal alkynyl sites connected with a phosphonium group via different π-conjugated linkers have been synthesized. The compounds themselves are efficient push–pull emitters and exhibit bright fluorescence in blue and near-UV regions. P1–P4 were used as alkynyl ligands to obtain a series of homoleptic bis-alkynyl Au(I) complexes 1–4. The complexes demonstrate bright phosphorescence and dual emission with dominating phosphorescence (2–4). Terphenyl derivative complex 3 exhibits warm white emission in DMSO solution and pure white emission in PMMA films. Time-dependent density functional theory calculations have shown that the T1 excited state has a hybrid MLCT/ILCT nature with a dominant contribution of charge transfer across a ligand-centered “D-π-A” system. The variation of linker allows tuning the effect of intermolecular charge transfer and thus changing the electronic and photophysical properties of the organogold “D-π-A” system. The results presented unambiguously display the advances of the conception of organometallic “D-π-A” construction.

Homoleptic Alkynylpyridinium Au(I) Complexes as Organometallic ‘D‐π‐A’ Chromophores

“…The values of excited state lifetimes are of nanosecond range, and the emission intensity does not dependent on oxygen presence, which is a clear indication of fluorescent nature of luminescence. The values of Stokes shifts for N2[OTf] and N3[OTf] are substantially higher than the ones for recently reported similar phosphonium derivatives [26] . The observed phenomenon may be related to the twisted intramolecular charge transfer (TICT) in the pyridinium salts [44] …”

“…Compared with alkynylphosphonium Au(I) complexes, [26] the synthesis of pyridinium analogs using a classical implementation of the ‘acac’ method is complicated due to poor solubility of N1[X] − N3[X] compounds in DCM as well as undesirable precipitation of insoluble [Au(acac) 2 ][Au(C 2 (C 6 H 4 ) n C 5 H 4 N + Me) 2 ] derivatives. Only the complexes 3[OTf] and 3[BARF] could be obtained by mild synthesis in DCM.…”

“…The syntheses of Au(I) complexes 1[X]À 3[X] (OTf and BARF salts) were carried out using the so called 'acac' method (Scheme 2). [38] Compared with alkynylphosphonium Au(I) complexes, [26] the synthesis of pyridinium analogs using a classical implementation of the 'acac' method is complicated due to poor solubility of N1[X]À N3[X] compounds in DCM as well as undesirable precipitation of insoluble [Au(acac…”

“…The values of Stokes shifts for N2[OTf] and N3[OTf] are substantially higher than the ones for recently reported similar phosphonium derivatives. [26] The observed phenomenon may be related to the twisted intramolecular charge transfer (TICT) in the pyridinium salts. [44] The cations N1 À N3 bearing strongly polarizing pyridinium group, belong to a class of activated terminal alkynes.…”

“…[25] Recently, we have reported a series of highly emissive bisalkynyl Au(I) complexes, involving phosphonium-based 'D-π-A' ('Donor-π-linker-acceptor') chromophore system connected to the gold center via π-conjugated linkers (Scheme 1). [26] Photophysical behavior of these Au(I) systems arises from the hybrid MLCT/ICT mechanism. The high values of phosphorescence quantum yields, dual emission behavior and the possibility of tuning the emission properties by variation of the π-linker have prompted us to further development of this class of compounds.…”