Cationic Dithieno[3,2-b:2‘,3‘-d]phospholes:  A New Building Block for Luminescent, Conjugated Polyelectrolytes

Abstract

Cationic dithieno[3,2-b:2',3'-d]phospholes are accessible very efficiently by methylation of the phosphorus center. Further functionalization with bromo substituents in 2,6-positions affords a polymerizable monomer that can be copolymerized with a difunctionalized fluorene in a Suzuki-Miyaura-type cross-coupling protocol. The monomers as well as the resulting conjugated polyelectrolyte based on the phospholium units show very intriguing photoluminescence properties, even in the solid state. [structure: see text]

Phosphorus‐Based Heteropentacenes: Efficiently Tunable Materials for Organic n‐Type Semiconductors

“…However, low‐energy transitions that indicate aurophilic interactions21 could not be observed in the fluorescence spectra of this compound. This observation is consistent with other dithienophosphole gold complexes reported by us earlier 24d,e…”

“…The PMe bond length of 1.763(3) Å is somewhat shorter than that of the few other structurally characterized phospholium salts (1.775(3)–1.787(5) Å) 32. The bond lengths in the dithienophosphole subunit are comparable to those in phospholium salt B (R=Ph; R′=H, E=Me + ) 24d. Again, the slight differences can be explained by the more extended π system consisting of five rings.…”

“…Reaction of 3 with methyl iodide as methylating agent was significantly slower. The 31 P NMR spectrum of 8 shows a singlet at δ =13.2 ppm that is significantly shifted from that of the starting material 3 ( δ =−25.1 ppm) and is characteristic for dithienophospholium compounds 24d. Compound 8 exhibits yellow fluorescence in solution ( λ ex =433, λ em =520 nm) with the largest redshift of this family of materials, due to the cationic nature of the phosphorus atom, which makes it an exceptionally strong acceptor center.…”

“…Compound 8 exhibits yellow fluorescence in solution ( λ ex =433, λ em =520 nm) with the largest redshift of this family of materials, due to the cationic nature of the phosphorus atom, which makes it an exceptionally strong acceptor center. The higher wavelength emission maximum of 8 with respect to dithienophospholium salt B (R=Ph, R′=H, E=Me + ),24d and derivative A (E=Me + ) investigated by Réau et al 20c. indicates further lowering of the LUMO level in combination with an extensively delocalized π system in 8 .…”

Selective Tuning of the Band Gap of π‐Conjugated Dithieno[3,2‐b:2′,3′‐d]phospholes toward Different Emission Colors

“…Suitable substituents for this purpose could either be alkyls such as 2‐ethylhexyl or functionalized phenyl groups. Studies toward the synthesis of suitable dithienophosphole monomers and corresponding polymers are currently underway 28…”