Synthesis and optoelectronic properties of transition metal complexes incorporating dithieno[3,2-b:2′,3′-d]phosphole ligands

Abstract

A series of dithieno[3,2-b:2',3'-d]phosphole-based transition metal complexes, including Au, Fe, Pt, Rh and W as central metals have been synthesised and characterised. Structural investigations by X-ray single crystal crystallography supported the high degree of pi-conjugation in the dithienophosphole ligands. This essential requirement for potential applications in molecular electronics and optoelectronics provides small band gaps for the materials. Investigations toward the optoelectronic properties of the respective complexes by fluorescence spectroscopy indicated that systematic alterations of the electronic structure are connected to different variables such as transition metal employed, functionalisation of the dithienophosphole ligands as well as complex geometries. The investigated Pt-based complexes exhibit only poor photoluminescence whereas Rh-, W- and Fe-based species with silyl functionalised dithienophosphole ligands show appreciable photophysical properties. The Au complexes investigated exhibit strong photoluminescence properties with very intriguing features in terms of excitation and emission wavelengths, intensity as well as selectivity.

Synthesis and Photophysical Properties of Donor–Acceptor Dithienophospholes

“…These results are quite remarkable since it has commonly been observed that oxidation of the phosphorus atom is accompanied by a redshift (Ͻ40 nm) in the absorption and emission spectra. [28] The same is true for transition-metal-complexed phospholes, which undergo a less pronounced bathochromic shift (Ͻ20 nm) [28,30] compared to noncoordinated dithienophospholes. In this case, the very slight changes in the absorption spectra reveal that the oxidation and complexation of the phosphorus atom located at the center of the π-conjugated molecules have almost no effect on the linear absorption properties of the system.…”

“…As mentioned above, it has been demonstrated that 3D branched molecules can potentially lead to synergistic effects by through-space interactions enhancing the TPA features. [17] The intriguing optoelectronic properties demonstrated by dithienophosphole gold complexes in general, [30] encouraged us to use the gold(I) chloride fragment as an out-of-plane unit. Treatment of 3 with Au(THT)Cl (THT = tetrahydrothiophene) at room temperature provided the corresponding donor-acceptor phosphole gold complex 5 in excellent yield (96 %); the characteristic 31 P{ 1 H} NMR signal at δ = 8.9 ppm confirmed its successful formation.…”

“…Treatment of 3 with Au(THT)Cl (THT = tetrahydrothiophene) at room temperature provided the corresponding donor-acceptor phosphole gold complex 5 in excellent yield (96 %); the characteristic 31 P{ 1 H} NMR signal at δ = 8.9 ppm confirmed its successful formation. [30] All new compounds were fully characterized by heteronuclear NMR spectroscopy ( 1 H, 13 C, 31 P), mass spectrometry, and elemental analysis. Complete data are provided in the Experimental Section.…”

“…[27] A few years ago, we introduced the dithieno[3,2-b:2Ј,3Ј-d]-phosphole as a novel phosphorus-based building block, [28] which has successfully been employed in a variety of materials, ranging from oligomers to polymers and dendrimers with excellent optical properties. [28][29][30] The unique structural and photophysical properties of this distinct type of phosphole, such as its versatile reactivity, tunability, and intense fluorescence with high quantum yields, make it particularly attractive in the conception of new and improved materials. The ideal materials design for NLO applications requires the structure and, more importantly, the photophysical properties of TPA chromophores to be adaptable to a specific function.…”

Transition-Metal Carbonyl Complexes of 2,5-Diferrocenyl-1-phenyl-1H-phosphole

“…The C−C and P−C bond lengths are similar for both complexes ( Figure 1). The Mo−C CO bonds for cis-CO in 3b range between 2.042(2) and 2.059(2) Å, while the shortest bond is observed for trans-CO (2.012(2) Å), which is in accordance with the stronger M−C CO back-bonding for the trans-CO. 57 17 The tetracarbonyltungsten complex 4c ( Figure 2) shows a distorted-octahedral environment around the tungsten atom with cis-oriented phosphole units. As already discussed for 3b,c, the W−C CO bond for trans-CO (1.990(3) Å) is shorter than that for the cis-COs (2.040(3) Å), indicating that the phosphole is a weaker π-acceptor ligand than the carbonyl groups.…”