The crystal structure of 3-([1,1′-biphenyl]-2-yl)-1,2-diphenylbenzo[b]phosphole-1-oxide, C₃₂H₂₃OP

Source of materials

A modified synthesis similar to a previously reported one was performed [5]: 1-(o-biphenylyl)-2-phenylethyne (5 mmol), diphenylphosphine oxide (10 mmol), and K₂S₂O₈ (15 mmol) were added to a sealed tube under argon, and then CH₃CN (20 mL) was added to the reaction tube by syringe. The reaction mixture was kept stirring at 100 °C for 20 h and then was cooled down to ambient temperature. After the reaction was quenched by adding the concentrated aqueous NaCl solution, the aqueous phase was extracted with 3 × 20 mL of CH₂Cl₂. The organic phase was dried using MgSO₄, filtered, and the solvent was removed in vacuo. The residue was column chromatography (petroleum ether/ethyl acetate) to afford the title compound (1.6 g, 71%). Crystals of the title compound were obtained by slow evaporation (n-hexane/CH₂C_l2) within seven days.

Experimental details

Coordinates of hydrogen atoms were added using riding models. Their U_iso values were set to 1.2U_eq of the parent atoms.

Comment

Many efforts have been devoted to the development of aggregation-induced emission (AIE) [6]. To date, the primarily accepted AIE mechanism of AIE is derived from the restriction of intramolecular motion including intramolecular rotations and intramolecular vibrations [7]. Therefore, the study on intramolecular motion-mechanical property relationship has received an unprecedented amount of attention [8, 9]. Recently, the benzophosphole-cores, phosphindole oxides, were developed to construct AIEgens [10], because of their unique high stabilities and electronic structures. Their impacts of steric, conjugation and electronic effects on the AIE properties were also showed based on the results of crystallography analysis [11]. The structure-property relationship is of crucial importance for the fundamental understanding and application exploration on AIE luminogens. Therefore, the crystal structure of benzo[b]phosphole with rotatable π-conjugated planes is crucial for understanding their intramolecular motion-mechanical property relationships.

The title compound (see the Figure) consists of a benzo[b]phosphole-core and two rotatable π-conjugated subunits (phenyl and biphenyl). The benzo[b]phosphole-core keeps a perfect co-plane and the quinquevalent phosphorus with four ligands shows a tetrahedral geometry, where the dihedral angle between the phosphole plane and the plane of the phenyl group of the P-substituent is 86.41° due to intramolecular hydrogen-bond of O–H–C20 (2.6023(14) Å). In addition, the motion-restricted o-biphenyl and motion-free phenyl are linked to adjacent C7 (bond length of C7–C21 is 1.486(2) Å) and C8 (bond length of C8–C9 is 1.475(2) Å), respectively.