Effects of boryl, phosphino, and phosphonio substituents on optical, electrochemical, and photophysical properties of 2,5-dithienylphospholes and 2-phenyl-5-thienylphospholes

• Published in: Dalton transactions : an international journal of inorganic chemistry 2016-01, Vol.45 (5), p.219-22
• Main Authors: Koyanagi, Yoshinari, Kimura, Yoshifumi, Matano, Yoshihiro
• Format: Article
• Language: English
• Subjects: Anions; Density functional theory; Derivatives; Emittance; Fluorescence; Mathematical analysis; Molecular orbitals; Optical properties
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c5dt03362d

The optical, electrochemical, and photophysical properties of Mes 2 B- (Mes = 2,4,6-trimethylphenyl), Ph 2 P-, or Ph 2 MeP + -substituted 2,5-dithienylphospholes and 2-phenyl-5-thienylphospholes are reported. The Mes 2 B- and Ph 2 P-substituted derivatives were prepared via regioselective lithiation and metathesis at the thiophene rings of the corresponding unsubstituted π-systems. The Ph 2 MeP + -substituted derivatives (phosphonium salts) were obtained via methylation of the Ph 2 P-substituted π-systems. The optical and electrochemical data and density functional theory calculations showed that the highest occupied molecular orbital and lowest unoccupied molecular orbital energies of these α,α′-linked thiophene-phosphole π-systems were sensitive to the intrinsic nature of the B and P substituents. The fluorescence quantum yields ( Φ f ) of the Ph 2 MeP + -substituted derivatives varied considerably depending on the counter anion, concentration, and solvent, but the π-π* transition energies were unchanged. The emitting ability of the Ph 2 MeP + -substituted 2,5-dithienylphosphole π-system changed significantly from Φ f = 0.07 to 0.87. These findings were investigated using time-resolved fluorescence spectroscopy and fluorescence titration measurements. The results show that phosphonium iodides were present in the equilibrium mixtures of three or two emitting ion pairs in CH 2 Cl 2 . The light-emitting abilities of the Ph 2 MeP + -substituted derivatives rely on heavy atom effects derived from the counter halide anions. The optical, electrochemical, and photophysical properties of α,α′-linked phosphole-thiophene π-systems bearing boryl, phosphino, or phosphonio groups were studied.