Photoluminescence-detected magnetic-resonance study of fullerene-doped π-conjugated polymers

Abstract

X-band photoluminescence (PL)-detected magnetic resonance (PLDMR) spectra of ${\mathrm{C}}_{60}$- and ${\mathrm{C}}_{70}$-doped 2,5-dihexoxy poly(p-phenylenevinylene) (DHO-PPV), 2,5-dibutoxy poly(p-phenylene ethynylene) (DBO-PPE), and poly(3-dodecylthiophene) (P3DT) are described and discussed. While light doping of DHO-PPV by both fullerenes quenches the PL, both the polaron and triplet exciton resonances are dramatically enhanced. This is attributed to the creation of conformational defects which enhance the fission of $1^1$ ${\mathit{B}}_{\mathit{u}}$ singlet excitons to polaron pairs and intersystem crossing to $1^3$ ${\mathit{B}}_{\mathit{u}}$ triplet excitons. The triplet resonance in all polymers is quenched at relatively low doping levels of ${\mathrm{C}}_{60}$ and ${\mathrm{C}}_{70}$, which is attributed to quenching of triplets by positive polarons injected onto the polymer chain. Increased doping by ${\mathrm{C}}_{60}$, but not ${\mathrm{C}}_{70}$, quenches the polaron resonance, also due to photoinduced charge transfer.