Synthesis of Pyridinothienogermoles as Unsymmetrically Condensed Germoles

Abstract

Pyridinothienogermoles (PyTGs) were prepared by the reaction of dilithiopyridylthiophene with dichlorodi(noctyl)germane and dichlorodiphenylgermane, and their electronic states were investigated by optical measurements and density functional theory (DFT) calculations. Bromination of trimethylsilyl-substituted PyTG with N-bromosuccinimide gave PyTG bromide, and palladium-catalyzed Stille coupling reactions of bromide with diphenyl[(trimethylstannyl)phenyl]amine and N-[(trimethylstannyl)phenyl]carbazole provided donor−acceptor compounds with pyridine as the acceptor and triphenylamine or phenylcarbazole as the donor. These compounds showed clear solvatochromic properties in the photoluminescence (PL) spectra. Bi(pyridinothienogermole) was prepared by the Stille coupling of DPyG bromide and trimethylstannyl-substituted DPyG. The Lewis basicity of the pyridine ring made it possible to use these DPyG derivatives as ligands for complex formation. Protonation and complex formation of the PyTG pyridine unit with tris(pentafluorophenyl)borane enhanced the donor−acceptor interaction, shifting the UV absorption and PL bands to lower energies.

Synthesis of Unsymmetrically Condensed Benzo- and Thienotriazologermoles

“…Replacing benzene with thiophene in TTAG caused a bathochromic shift of 13 nm to give an absorption maximum at 294 nm in THF. When compared with thienopyridinogermole, the absorption maximum of TTAG was shifted to the shorter wavelength region by 6 nm, reflecting the less extended conjugation of thienyltriazole than thienylpyridine [ 26 ]. In fact, 5-trimethylsilyl-2-thienylpyridine possesses the absorption maximum at 324 nm, redshifted by approximately 40 nm compared to that of TT-TMS [ 26 ].…”

“…When compared with thienopyridinogermole, the absorption maximum of TTAG was shifted to the shorter wavelength region by 6 nm, reflecting the less extended conjugation of thienyltriazole than thienylpyridine [ 26 ]. In fact, 5-trimethylsilyl-2-thienylpyridine possesses the absorption maximum at 324 nm, redshifted by approximately 40 nm compared to that of TT-TMS [ 26 ]. Silyl substitution at the α-position of the thiophene ring in TTAG-TMS shifted the absorption maximum slightly to 286 nm.…”

“…A linear relationship between the Stokes shifts and orientational polarizabilities was observed ( Figure 2 and Table S1 ). Using the slope of the Lippert–Mataga plot, the dipole moment change (Δ μ ) upon photoexcitation was calculated to be 18.4 D ( Figure S2 ) [ 26 ]. This was smaller than that calculated for thienopyridinogermole with the same substituents (19.9 D), suggesting that fine tuning of the D–A interaction is possible by changing the acceptor unit.…”

“…Si/Ge-condensed compounds, such as siloles and germoles, have received considerable attention in recent decades for their potential applications in organic electronics [ 25 , 26 ]. These structures exhibit a notable phenomenon known as σ*–π* conjugation, which is frequently observed between Si/Ge σ*-orbitals and endocyclic butadiene π*-orbitals.…”

“…Currently, dithienosilole and dithienogermole are used as building units for preparing conjugated functional materials for optoelectronic devices, such as OLEDs [ 31 ], organic solar cells [ 32 ], and organic transistors [ 33 ]. However, most condensed siloles and germoles reported so far possess symmetrical tricyclic systems [ 34 ], and studies on unsymmetrical tricyclic systems have been limited to simple cases, such as combinations of benzene–pyridine [ 35 , 36 ], benzene–thiophene [ 37 , 38 ], and thiophene–pyridine ring systems [ 26 ].…”