Directional energy migration in an oriented nanometer-scale host/guest composite: semiconducting polymers threaded into mesoporous silica

In this paper, we show that the semiconducting polymer poly[2-methoxy-5-(2 ' -ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) can be incorporated into the channels of an aligned mesoporous silica host. Polarized fluorescence spectroscopy is used to show that more than 80% of the polymer in the composite is aligned by incorporation into the host. Time-resolved transient absorption spectroscopy further indicates that the incorporated chains are isolated from each other, while the unincorporated polymer is aggregated, probably at grain boundaries or surfaces. Control of the fraction of polymer inside versus outside the pores can be achieved by selective oxidation of the unincorporated polymer. Because of the unique nanoscale geometry of this material and the existence of multiple environments, excitations in this composite are funneled from outside the pores down into the aligned, isolated polymer chains inside the pores. Time-resolved stimulated emission spectroscopy is used to follow this process by monitoring the increase in luminesce polarization with time. The results show that control of polymer morphology through host/guest chemistry can be used to direct the motion of excitations and thus to deliver energy to specific regions of a material. (C) 2001 Elsevier Science B.V. All rights reserved.