Novel silicon-based copolymers show the UV-visible strong absorption bands around 347-387 nm. Their maximum photoluminescence (PL) wavelengths for silicon-based copolymers appeared around 420-480 nm in the blue region. The present copolymers with a relatively short π-conjugation length exhibit blue light-emitting diodes (LED) at the low operating voltages, due to the reduction of the LUMO level in luminescent polymers by introducing silicon atoms in luminescent polymers as well as the d-orbital participation of silicon atoms.
|Number of pages||6|
|Journal||Molecular Crystals and Liquid Crystals Science and Technology Section A: Molecular Crystals and Liquid Crystals|
|Publication status||Published - 1999|
Bibliographical noteFunding Information:
Considering the above results, it is not unreasonable to suppose that the shorter wavelength emission band results from carbazole segments. Meanwhile, it is not straightforward to assign the origin of the longer wavelength emission band to the PPV segment in the SiPhPVK, because no such a longer wavelength emission band is found in either PL or EL spectra from a SiPhPPV thin film which show the luminescence band maximum at the wavelength of 450 nm. The longer wavelength emission band from both PL and EL of the SiPhPVK might be explained by proposing the involvement of a certain type of excited states, such as the inter-or intramolecular exciplex formed between an excited-state carbazole and a PPV segment and the intermolecular excimer between carbazole moieties. But the absence of the PL band at around 530 nm in the wide concentration range in its solution led us to confirm that any type of intramolecular interaction is not adequate for that radiative transition. And also, the longer wavelength emission is mainly due to the optical excitation to PPV main chain, not due to that of a carbazole unit. Furthermore, the carbazole segment in our SiPhPVK have a branched, bulk alkyl chain, which should reduce the probability of the proposed excimer. So, it is not likely to explain the origin of the longer wavelength emission as the proposed excimer or exciplex. The other probable explanation can be drawn from the supposition that the effective conjugation length in excited state be remarkably increased due to the interaction between silicon moiety and carbazole through x-electronic system of SiPhPVK, compared to those in ground state. Unfortunately, no direct evidence was observed for this proposition till now. Investigation on the relaxation dynamics of SiPhPVK upon selective photoexciation of the two electronic transition might be useful to have a deeper understandings on these interesting phenomena. This work was financially supported through the advanced materials research program in 1998 (HKK) from the Ministry of Education and the Star Project (SCJ) from MOST, Korea.
All Science Journal Classification (ASJC) codes
- Condensed Matter Physics