The spectroscopic and photophysical properties of silicon-containing styryl-carbazole were investigated in various solvents, and the results were analyzed with reference to its carbon derivatives. In n-hexane, both the silicon- and the carbon-containing compounds had very similar emission properties. In acetonitrile, the emission properties remained the same for the C-compound but changed significantly for the Si-compounds. In particular, the fluorescence spectra of the latter were red-shifted, and their radiative rate constants were even 7 times larger than in n-hexane, which suggested that the emissive states of the silicon-containing compounds were different in these two solvents. DFT calculations using the CAM-B3LYP functional showed that the emissive state of the C-compound involves the LUMO+1 orbital regardless of the medium. In contrast, for the Si-compound, changing the medium from n-hexane to acetonitrile resulted in the inversion of the emissive states from an excited state involving the LUMO+1 orbital (the dipole moment μ = 4.2 D) to an excited state involving the LUMO orbital (μ = 8.9 D).
Styrylcarbazole linked
to pyrene by a dimethylsilyl bridge was
synthesized in the search for new charge-transfer active materials
for LED applications. In the course of a photophysical study, it turned
out that such a donor-bridge-acceptor compound displayed three completely
different types of emission depending on solvent polarity. The most
attractive emission properties were found in acetonitrile in which
two broad emission bands were observed. The resolved mechanism of
the excited-state processes in acetonitrile was supported by singular
value decomposition with self-modeling treatment of time-resolved
emission spectra (ns-TCSPC). The data analysis revealed that there
were two excited-state processes, that is, charge transfer within
styrylcarbazole and electron transfer from styrylcarbazole to pyrene
through a silylene bridge that was responsible for a broad dual emission.
The general idea of designing compounds that display emission from
more than one excited state covering a wide range of the visible spectrum
can be a powerful tool in designing new white-light-emitting materials.
Herein, an effective and selective synthesis of chromophore-functionalized monovinylsilsesquioxane derivatives by a cross-metathesis reaction along with discussion of their photophysical and thermal resistance properties is disclosed.
Enhanced emission of 4,4′-bis(vinyldimethylsilyl)-biphenyl as compared to its carbon analogue resulted from the presence of the silicon atom that caused stronger transition moment of the emissive state and more efficient mixing of the excited states.
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