Supramolecular confinement and photoluminescence enhancements of a conjugated polymer by hydrogen bonding in solid films

Massive photoluminescence (PL) enhancements and blue shifts in solid films of a conjugated polymer (CP) were observed when supramolecular confinement took effect under intermolecular hydrogen bonding (HB) stabilized via paired diluent interactions. By blending a HB donor diluent of 4-octylphenol into poly [2-(thiophen-3-yl)ethyl acetate], a CP with HB acceptor side-groups, the PL emissions and blue shift surged at a threshold diluent fraction (phi d) corresponding to -0.5 diluent molecule per CP monomers, attributed to molecular confinement by the hydrogen bonding. The confinement culminated, with the PL enhancements and blue shift achieving -12 folds and -40 nm respectively, at phi d -1.5 diluent per monomer when almost all CP side-groups had formed supramolecular bonding; thereafter it plateaued as the excess diluent precipitated into crystalline 2nd phase. It is inferred that restriction of CP motions under supramolecular confinements can rigidify the backbones to lead to reduced self-trapping and enhanced PL, while at the same time the incurred modification of chain conformations disrupts conjugation lengths and gives rise to large blue shifts.