Organic π-conjugated molecules offer great potential for nonlinear optics applications due to their structural flexibility and favorable emissive properties. Diketopyrrolopyrrole (DPP) derivatives, known for their high planarity and excellent emissive properties, are particularly attractive for such research. In this study, we investigated excited state absorption (ESA) in two DPP derivatives with thienyl groups and different peripheral substituents (hydrogen and bromine) using Z-scan and pump-and-probe techniques. The presence of the bromine atom resulted in a significantly higher nonlinear response, as evidenced by an ESA band at 415 nm with a cross-section 15 times larger than the ground state. Additionally, the sample with bromine exhibited a twofold increase in the cross-section. These findings establish DPP derivatives as promising materials for photonic device applications.
The growing interest in fluorescent molecules capable of absorbing two photons has been driven by their significance in two-photon absorption (2PA) microscopy. However, challenges persist due to low 2PA in small molecules. Derivatives of dithienyl-diketopyrrolopyrrole (DPP2Ts) offer a solution with their easily modifiable nature, high fluorescence quantum yield, and structural planarity. In this work, two symmetric DPP2T derivatives were studied, exploring the influence of bromine on 2PA using the Z-scan technique. The results showed absorption in the near-infrared with a 1.4-fold increase in 2PA values (19-27 GM) due to the presence of bromine. However, bromine negatively affected emissive properties, reducing fluorescence from 73% to 56%. These findings hold promise for the utilization of DPP2Ts as fluorescent markers.
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