Fluorescence properties of π-conjugated polymers in porous silica

The fluorescence properties of poly(2,6-(4-phenylquinoline)) (PPQ) and poly(ethylene glycol)-b-poly(p-phenylene ethynylene)-b-poly(ethylene glycol) (triblock) within porous glass were investigated. Emission was shifted to different wavelengths by varying the pore size. The emission shift is attributed to the unique aggregation state at each pore size. At small pore sizes (similar to8 nm), the polymers emit lights as the monomer-like states (490 nm for PPQ and 420 nm for triblock when excited at 365 nm). The emission shifts to the red region as the pore size increases until it reaches 30 nm at which PPQ emits light at 545 nm and triblock at 500 nm. As the pore size continues to increase, there is sufficient space for the relatively smaller PPQ to orient in different directions, reducing the interchain interaction and causing the emission to be blue-shifted to similar to500 nm. The bulky triblock, however, prevents the polymer from orienting randomly, obliging the chains to align in a relatively planar geometry and retaining a strong interchain interaction.