From Model Compounds to Extended π‐Conjugated Systems: Synthesis and Properties of Dithieno[3,2‐b:2′,3′‐d]phospholes

Abstract

To explore their suitability for applications in molecular optoelectronics and as sensory materials, novel dithieno[3,2-b:2',3'-d]phospholes have been synthesized and their reactivity and properties investigated. An efficient two-step synthesis allowed for a modular assembly of differently functionalized compounds. The dithieno[3,2-b:2',3'-d]phosphole system exhibits extraordinary optoelectronic properties with respect to wavelength, intensity, and tunability. Owing to the nucleophilic nature of the central phosphorus atom, its significant electronic influence on the conjugated pi system can be altered selectively by chemically facile modifications such as oxidation or complexation with Lewis acids or transition metals. All the dithienophosphole species presented show very strong blue photoluminescence with excellent quantum yield efficiencies supporting their potential utility as blue-light emitting components in organic light emitting diodes (OLEDs). Furthermore, depending on the electronic nature of the phosphorus center, the materials exhibit distinctive optoelectronic properties suggesting that the dithieno[3,2-b:2',3'-d]phosphole system may be useful as sensory material. Theoretical calculations, including time-dependent DFT methods, revealed the excellent predictability of the structures and optoelectronic properties of the functionalized dithienophospholes allowing the design of future dithieno[3,2-b:2',3'-d]phosphole-based materials to be "stream-lined". By using tin-functionalized dithienophosphole monomers, a strategy, which involves Stille coupling, towards extended pi-conjugated materials with significantly redshifted optoelectronic properties is also presented.

Dendrimeric Oligo(phenylenevinylene)‐Extended Dithieno[3,2‐b:2′,3′‐d]phospholes—Synthesis, Self‐Organization, and Optical Properties

“…[16] Complete conversion of the trivalent phosphorus center to the phosphole oxide can be monitored by 31 P NMR spectroscopy, showing a distinct lowfield shift for the product 5 at d = 18.6 ppm that is typical for these compounds; 1 H and 13 C NMR spectra also show consistent data. Another indication of the successful transformation of 5 is the fluorescence emission at l em = 551 nm that is red-shifted by about Dl em = 44 nm from that of the non-oxidized starting material; oxidation of the phosphorus center in dithienophospholes in general affords a red-shift of 40-50 nm due to a lowered LUMO level.…”

“…To improve the acceptor properties of the central phosphorus atom, [16,17] as well as to obtain a suitable photophysical reference material for the targeted dendrimers (vide infra), we oxidized the phosphorus atom of the phenyl-A C H T U N G T R E N N U N G vinylene extended compound 4 a in our typical protocol using hydrogen peroxide in dichloromethane at room temperature. [16] Complete conversion of the trivalent phosphorus center to the phosphole oxide can be monitored by 31 P NMR spectroscopy, showing a distinct lowfield shift for the product 5 at d = 18.6 ppm that is typical for these compounds; 1 H and 13 C NMR spectra also show consistent data.…”

“…[15] A few years ago, we introduced the dithieno[3,2-b:2',3'-d]phos-A C H T U N G T R E N N U N G phole system (1, Scheme 1) to this field of research. [16] Our building block, which conjoins two thiophene subunits with a central phosphole moiety through annelation, allows for the selective and efficient tuning of the (opto)electronic properties of the materials by functionalization of phosphorus atom or the main scaffold. [16,17] The materials obtained in the context of our studies, display highly advantageous, unprecedented photophysical properties with respect to emission wavelengths, intensity, and tunability.…”

Synthesis and X-ray single-crystal structure study of 5,5′-bis(silyl)-functionalized 3,3′-dibromo-2,2′-dithiophenes

“…In the context of our work on phosphorus-thiophene hybrid materials for molecular electronics, we rely on the title compounds as starting materials for the synthesis of dithieno[3,2-b : 2 ,3 -d]phospholes (1). 3,4 It should be mentioned that 3,3 -dibromo-5,5 -bis(trimethylsilyl)-2,2 -dithiophene (see Scheme 1, SiR 3 = SiMe 3 ), which is comparable to the compounds presented, has been described by Ohshita et al 5 before; however, the yield of the product obtained is reduced due to an extensive work up.…”

“…3,3 ,5,5 -Tetrabromo-2,2 -bithiophene (2) was prepared by literature methods. 6 The title compounds were prepared according to the reported procedure in the case of 5 3,4 Suitable single crystals for X-ray structure studies of 3 and 5 were obtained from concentrated pentane solutions at room temperature.…”