Base-Mediated Cyclization Reaction of 2-Alkynylphenylphosphine Oxides: Synthesis and Photophysical Properties of Benzo[b]phosphole Oxides

Abstract

The base-mediated intramolecular cyclization reaction of 2-alkynylphenylphosphine oxides affords benzo[b]phosphole oxides, which show intense blue-green fluorescence. Benzo[b]phospholes are also prepared by the reduction of benzo[b]phosphole oxides.Among the variety of π-conjugated systems with potential applications as electronic materials, such as organic thin film transistors and organic electroluminescent (EL) devices, main group element-containing π-conjugated molecules have attracted considerable interest recently. 1 This is because the orbital interaction of the main group element moiety plays an intriguing role in the π-conjugated framework, and the resultant π-systems reduce the HOMO-LUMO gaps compared with the parent π-system. In this context, phosphacyclopentadienes (phospholes) form interesting building blocks for the construction of conjugated systems, where an interaction between the butadiene π* orbital and the lowlying σ*(P-R) orbital takes place in the ring. 2 In addition, phosphorus-containing π-systems retain a versatile reactivity of a central phosphorus atom, and this makes it possible to tune the electronic and optical properties of the materials using simple chemical modifications, such as oxidation. Several reports have addressed the synthesis of phospholes, 3,4 dibenzophospholes, 5,6 dithienophospholes, 7 andtheirderivatives. 8 Indoles are basic skeletons in organic chemistry and are found in natural products and biologically active substances. 9,10 On the other hand, synthesis and properties of benzo[b]phosphole, phosphorus analogues of indoles, have not been explored to date. 11,12 Here, we report the synthesis and photophysical properties of benzo[b]phosphole oxides and benzo[b]phospholes. [13][14][15] Because the metal-and base-mediated cyclization reaction of alkynylamines, which proceeds through intramolecular addition of the N-H bond to the triple bond, is one of the

Synthesis and Structure–Property Relationships of 2,2′‐Bis(benzo[b]phosphole) and 2,2′‐Benzo[b]phosphole–Benzo[b]heterole Hybrid π Systems

“…The prototype of this reaction was reported by Winter and Butters in the 1970s9 and has recently been improved by several research groups 3. In recent syntheses, Tsuji et al.,3a Sanji et al.,3b and Yamaguchi et al 3c. independently achieved the sequential introduction of π‐conjugative substituents at the phosphole α‐ and β‐carbon atoms in one‐pot or two‐step procedures.…”

Benzophosphole Oxide and Sulfide for Thermally Stable Cathode Buffer Layers in Organic Thin‐Film Photovoltaic Devices

“…Phosphole compounds have been receiving the attention of chemists owing to their potential use in materials research, [20][21][22][23][24][25][26][27][28][29] including their light-emitting properties to be applied to organic light-emitting diodes (OLEDs). [30,31] We have shown above that the benzophosphole derivatives are also useful as cathode buffer materials for OPV devices.…”

Pluripotent Features of Doubly Thiophene‐Fused Benzodiphospholes as Organic Functional Materials

“…On the other hand, cis ‐ 1 reveals a slightly warped structure, which probably originates from the packing forces (Figure b). The C−C and C−P bond lengths of the benzodiphosphole unit are similar to those of reported benzodiphospholes;,, thus indicating that the fusion of thiophene to the benzodiphosphole has little impact on their structural parameters (Figures S1 and S2 in the Supporting Information). The trans and cis isomers reveal unusual contrasts in packing modes.…”

“…Phenyl‐substituted doubly thiophene‐fused benzodiphospholes 2 a – c display redshifted absorption and fluorescence spectra, compared with that of unsubstituted trans ‐ 1 (Figure ). The thiophene‐fused structure is responsible for the redshifted absorption of 2 a ( λ =443 nm), relative to those of the phenyl‐substituted benzodiphospholes ( λ ≈425 nm) ,. Dimethylaminophenyl‐substituted 2 b reveals a redshifted intense absorption at λ =505 nm, in comparison with 2 a , which indicates effective ICT interactions between the electron‐donating dimethylamino moiety and electron‐withdrawing benzodiphosphole unit.…”

“…Despite extensive efforts to develop phosphole‐based ladder‐type π‐conjugated molecules, examples of benzodiphospholes are still rare. The first synthesis of phenyl‐substituted benzodiphosphole was reported by Tanaka and co‐workers in 2008 . Then, Yamaguchi et al.…”