Synthesis and two‐photon absorption properties of hyperbranched diketo‐pyrrolo‐pyrrole polymer with triphenylamine as the core

A novel hyperbranched polyyne ( hb ‐ DPP ) with triphenylamine as the core, 2,5‐dioctylpyrrolo [3,4‐c]pyrrole‐1,4 (2H,5H)‐dione ( DPP ) as the connecting unit has been designed and synthesized by Glaser‐Hay oxidative coupling reaction, which was characterized by IR, NMR, UV‐vis, FL, and GPC. The polymer exhibits high molecular weight ( M w up to ∼6.55 × 10 4 Da) and is readily soluble in common organic solvents such as toluene, chloroform, tetrahydrofuran, N,N ‐dimethyl formamide and so on. The one‐ and two‐photon absorption (TPA) properties have been investigated. The TPA cross section of the polymer was measured by open‐aperture Z‐scan experiment using 140 femtosecond (fs) pulse, and the TPA cross section for hb ‐ DPP was determined to be 579 GM per repeating unit at wavelength of 800 nm. In tetrahydrofuran, hb ‐ DPP exhibits intense frequency up‐converted fluorescence with the peak located at 584 nm under the excitation of 800 nm fs pulses.