Third-Order Nonlinear Optical Properties in the Excited State of Well-Defined Thiophene−Dimethylsilyl Co-oligomers

Abstract

A new series of oligomers for nonlinear optics (NLO), the thiophene−dimethylsilyl co-oligomers, (TSi) n −T with n = 1−3, have been synthesized in order to combine third-order NLO response and transparency in the visible region. Stationary-state absorption spectra, fluorescence spectra, and time-resolved absorption (picosecond) have been carried out. In sharp contrast with oligothiophenes, the absorption spectra of (TSi) n −T are not red-shifted as n increases, but as for short oligothiophenes their quantum yield of fluorescence is low because of the competitive triplet-state formation and their emission wavelength range is remarkably solvent-independent. These data show slight increase of the dipole moment between the S0 ground state and the S1 excited state, in agreement with theoretical calculations (ZINDO method). Fast intersystem crossing is observed between singlet and triplet states and S1 → S n and T1 → T n spectra have been measured. Optical nonlinearity (γ) of the excited state has been measured and compared to the terthiophene. The large molecular second hyperpolarizability of the silyl derivatives associated with their interesting transparency properties shows that such oligomers may be considered, in the excited state, as promising molecules for nonlinear applications.

Synthesis, Characterization and Optical Properties of a Novel Si-Containing σ-π-Conjugated Hyperbranched Polymer

“…ethynylbenzene in hexane: k max = 236 nm, e max = 12 500 m -1 cm -1 ). It has been reported that diarylsilanes (e. g., 4,49-substituted dimethyldiphenylsilane [19] and dimethyldithienylsilane [20] ) and hyper- branched poly(2,5-silylthiophenes) [5] show p-to-r charge transfer absorptions in the range 300-320 nm. Poly(1) displays a weak absorption around 330 nm, which is clearer and stronger than that of poly (2).…”

Alternating divinylarene–silylene copolymers

“…The interaction between the silylene group and the conjugated p-chromophore, if any, would be very weak. [11][12][13] For example, the very weak absorption at 310 nm for thiophene-dimethylsilylene co-oligomers 9 may arise from the transition involving charge transfer from the thiophene moiety to the dimethylsilylene group. 11 In addition, the weak Scheme 2 Scheme 1 absorption around 345 nm and structureless emission in a series of diphenylacetylene-dialkylsilylene copolymers 10 may be attributed to possible intramolecular charge transfer.…”

“…[11][12][13] For example, the very weak absorption at 310 nm for thiophene-dimethylsilylene co-oligomers 9 may arise from the transition involving charge transfer from the thiophene moiety to the dimethylsilylene group. 11 In addition, the weak Scheme 2 Scheme 1 absorption around 345 nm and structureless emission in a series of diphenylacetylene-dialkylsilylene copolymers 10 may be attributed to possible intramolecular charge transfer. 12 As mentioned earlier, when the conjugation length is increased, the s-p interaction between the silylene group and the oligothiophene moiety may become less important.…”

“…7 Delocalisation between Si-containing s-bonds and conjugated systems may dictate the electrical and optical properties associated with these materials. [8][9][10][11][12][13] The nature of the s-p conjugation has been extensively studied. Interaction of the high-lying Si-Si s-bonding orbital with the p*-orbital of the conjugated chromophore may readily occur.…”

“…Presumably, the energy difference between the Si-C bonding orbital and p*-orbital of the conjugated chromophore may be relatively large and, therefore, such interaction may be too weak to detect. Although there are reports on possible intramolecular charge transfer from conjugated chromophores to monosilylene species, 11,12 the details will be compared later in this feature article. It is noteworthy that, when the conjugation length is increased, s-p interaction between the silylene group and the p-chromophore may become less important.…”