Red-to-Near-Infrared Electroluminescence and Low-Threshold Amplified Spontaneous Emission from Solution-Processable Fluorescent Diketopyrrolopyrrole Derivatives

Abstract

A detailed investigation of the photophysical, electroluminescence, and amplified spontaneous emission (ASE) properties of two solution-processable fluorescent diketopyrrolopyrrole derivatives is reported. Photophysical measurements are carried out in solution and blend films containing a 4,4′-bis(N-carbazolyl)-1,10-biphenyl (CBP) or a poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(benzo[2,1,3]thiadiazol-4,8-diyl)] host, to gain important insights into the excited state behavior of these dyes. Quantum chemical calculations are also carried out to support the experimental findings. An optimization of the doping concentration in the CBP blends is necessary to reduce the strong aggregation. This optimization led for both near-infrared-emitting dyes to a substantial increase of the photoluminescence quantum yield, which can reach values as high as 60%. It is also found that the blend films show excellent ASE properties with a threshold as low as 3.5–4.5 μJ cm⁻² for peak wavelengths of 739 and 727 nm. In addition, the electroluminescence properties of the two organic laser dyes are examined in organic light-emitting diodes (OLEDs). The best OLED device shows a maximum external quantum efficiency value of around 2%. Overall, this study demonstrates the excellent potential of diketopyrrolopyrrole derivatives for high-performance near-infrared organic semiconductor lasers and provides useful information for the design of new efficient near-infrared emitters for optoelectronic applications.