Excitation energy migration in oligo(p-phenylenevinylene) based organogels: structure-property relationship and FRET efficiency.

Excitation energy migration (EM) and assisted energy transfer (ET) properties of a few oligo(p-phenylenevinylene) (OPV) based organogelators with different end functional groups have been studied using picosecond time-resolved emission spectroscopy (TRES). EM was found to be more efficient in OPV gelators with small end functional groups (OPV3-4) when compared to that of the gelators with bulky end groups (OPV1-2) in the gel state. TRES studies at elevated temperature and in chloroform solution highlight the role of the self-assembled scaffolds in assisting the EM and ET processes. Increase in temperature and solvent polarity leads to the aggregate breaking and hence adversely affects the EM and ET efficiencies. The effect of EM efficiency on the fluorescence resonance energy transfer (FRET) properties of the OPV gels was studied by using OPV1 and OPV3 as the donors and OPV5 as the acceptor. Better transfer of excitation energy was observed in the donor system (OPV3) having higher EM efficiency even at very low concentration (3.1 mol%) of the acceptor molecules, whereas ET efficiency was lower in the donor system (OPV1) with low EM efficiency.