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Encapsulation of luminescent polymers in porous alumina Kwong, Keri

Abstract

The incorporation of three conjugated polymers: MEH-PPV, DP-PPV and DP10- PPV into porous alumina films on Al, Si and ITO substrates via an adsorption process is reported. The nature of this adsorption process involves bonding between Lewis acidic Al centres on the alumina and the Lewis basic polymer backbone. The MEH-PPV porous alumina hybrids was found to degrade rapidly upon the irradiation of UV-light (λext = 366 nm) in air but to a lesser extent in the dark and under nitrogen. Silanization of the pores by treatment with trimethylchlorosilane (TMS), phenyldimethylchlorosilane (PDMS) and octyldimethylchlorosilane (ODMS) resulted in lower MEH-PPV loading in porous alumina membranes (Anodisc 13) relative to the membranes with unmodified pore walls. In the fluorescence spectra, the intensity of the fluorescence from the Anodisc membranes containing MEH-PPV is higher than from MEH-PPV in silanized porous alumina. The Lewis acidic Al centres of the porous alumina in the silanized pores are screened from the Lewis basic polymer resulting in a lower fluorescence intensity. Within the silanes used, the absorbance intensity is in the order: TMS > ODMS, PDMS. Within the silanes, the difference in fluorescence intensities may be due to the size of the alkyl/aryl groups. The larger alkyl substituent in ODMS and the aryl group in PDMS may act to better screen the Lewis acidic Al than in the smaller alkyl group in TMS. In DP10-PPV, the unmodified porous alumina has a higher fluorescence intensity relative to the modified materials. This is attributed to the interactions between the pore walls and the polymer. The same screening effect that occurs for MEH-PPV is also observed for DP10-PPV. For DP10-PPV, the fluorescence intensities is in the order: PDMS > ODMS, TMS. This difference may arise from the favourable π-stacking interactions between the polymer and the PDMS silanized pores.

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