Wavelength-Dependent Nonlinear Optical Activities of Near-Infrared Boron-Dipyrromethene Derivatives

Near-infrared (NIR) organic dyes with strong ultrafast nonlinear optical (NLO) activities are important for various applications. However, the study of the wavelength-dependent NLO properties of NIR dyes is still ongoing. In this work, we present the first comparison of the NLO properties of two NIR boron-dipyrromethene (BODIPY) derivatives at different excitation wavelengths, in which strong electron-donating groups, namely 4-(N,N-dimethylamino) phenyl and 1-ethyl-1,2,3,4- tetrahydroquinoline groups, are connected through the BODIPY cores. Results obtained from Z-scan experiments show that the two BODIPY derivatives exhibit strong saturable absorption and large modulation depth when excited by femtosecond pulses at 800 nm. With 1300 nm excitation, both derivatives exhibit strong nonlinear refraction. In addition, the derivatives also display effective two-photon action cross-sections in the wavelength range of 1200-1600 nm. They are potentially excellent nonlinear optical materials. This comprehensive comparison of the NLO properties of BODIPY derivatives can suggest new possibilities for the design and development of NIR NLO materials.