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 in to the channels of an aligned mesoporous silica host. Polarized fluorescenc e spectroscopy is used to show that more than 80% of the polymer in the com posite is aligned by incorporation into the host. Time-resolved transient a bsorption spectroscopy further indicates that the incorporated chains are i solated from each other, while the unincorporated polymer is aggregated, pr obably at grain boundaries or surfaces. Control of the fraction of polymer inside versus outside the pores can be achieved by selective oxidation of t he unincorporated polymer. Because of the unique nanoscale geometry of this material and the existence of multiple environments, excitations in this c omposite are funneled from outside the pores down into the aligned, isolate d polymer chains inside the pores. Time-resolved stimulated emission spectr oscopy is used to follow this process by monitoring the increase in lumines ce polarization with time. The results show that control of polymer morphol ogy through host/guest chemistry can be used to direct the motion of excita tions and thus to deliver energy to specific regions of a material. (C) 200 1 Elsevier Science B.V. All rights reserved.