Photoluminescence of Poly(P-Phenylene Vinylene) Encapsulated in Mesoporous Silica
- PDF / 276,858 Bytes
- 5 Pages / 394.2 x 628.2 pts Page_size
- 59 Downloads / 196 Views
ABSTRACT The preparation of poly(p-phenylene vinylene) (PPV) encapsulated in a mesoporous silica, MCM-41, is reported. In situ polymerization of xylylene bis(tetrahydrothiophenium chloride) yields a highly luminescent, yellow powder with a fluorescence spectrum matching that of unencapsulated PPV. Nitrogen adsorption isotherms show that the pore size of the PPVloaded MCM-41 is significantly smaller than that of empty MCM-41 and a polymer loading of ca. 8% by weight is obtained by thermogravimetric analysis. Photoluminescence data for the encapsulated PPV are presented. INTRODUCTION Electroluminescent (EL) devices prepared using conjugated polymers as the emitting layer were first reported in 1990 by Friend,1 and have been studied extensively in the last decade. 2 -4 Although progress has been achieved in extending device lifetime and increasing output brightness while decreasing operating voltage, there remain many fundamental questions regarding the processes occurring in these EL devices, notably charge injection, transport and recombination. We are interested in investigating the relative contributions of intrachain and interchain interactions to the recombination process in poly(p-phenylene vinylene) (PPV). Recently, Rothberg showed that interchain interactions in derivatives of PPV caused quenching of photoluminescence (PL) in these materials. 5 They conclude that intrachain excitons are primarily responsible for PL in PPV. In a related study, 6 Heller and coworkers isolated the polymer chains by preparing dilute blends and adding bulky substituents to the polymer. These studies are relevant to EL devices prepared using the same polymers, since PL yield provides an upper limit for EL yield from the same material. In this paper, we present a new approach to reduce interchain interactions in PPV by encapsulating it in MCM-41 and report preliminary PL data for these encapsulated materials. MCM-41 is a zeolitic material from the M41S family and consists of hexagonally-ordered onedimensional channels approximately 35 A in diameter separated by 5 A thick amorphous silica walls. 7 This material has a very high surface area (on the order of 1000 m2 g9, approximately 90% of which is internal surface area) and it has been found that 26-30% of all Si atoms bear a surface hydroxy group. 8 MCM-41 is synthesized by condensing silica around micelles formed by surfactant molecules; thus the pore size is determined by the size of the surfactant used. This flexibility and the large internal surface area makes MCM-41 an attractive host material and the synthesis of novel hybrid materials based on MCM-41 has been the subject of many recent reports.9, 10
319 Mat. Res. Soc. Symp. Proc. Vol. 558 ©2000 Materials Research Society
EXPERIMENTAL
Nitrogen adsorption analysis was obtained on a Micromeritics ASAP 2010 instrument 1 and the data analyzed using the Barrett-Joyner-Halenda (BJH) method. 1 The Harkins-Jura as recommended by layer, nitrogen equation was used to represent the thickness of the adsorbed Kruk and coworkers. 12 The
Data Loading...
