Enhanced Optical Limiting Effects in Porphyrin‐Covalently Functionalized Single‐Walled Carbon Nanotubes

Optical limiters are employed to protect sensitive optical components or eyes from laser-induced damage. [1,2] They have lower transmittance for high-intensity or fluence laser input while they keep a high linear transmittance. Many works have concentrated on creating ideal optical limiting devices by exploiting passive limiting mechanisms such as nonlinear absorption (multiphoton absorption, reverse saturable absorption (RSA)), nonlinear refraction (electronics or thermal effects), and nonlinear light scattering. Both single-walled carbon nanotube (SWNT) and multiwalled carbon nanotube (MWNT) suspensions have been reported to have strong optical limiting effects in the nanosecond regime, which arise from strong nonlinear light scatterings due to the creation of new scattering centers consisting of ionized carbon microplasmas and solvent microbubbles. [3–9] To promote their optical limiting effects, the optical nonlinear media with other optical nonlinear processes (e.g., two-photon absorption or RSA) have been blended with carbon nanotubes. [10,11] The association of SWNTs with organic chromophores having multiphoton absorption processes was recently shown to be a promising approach to achieve optical limiting systems with broad temporal and spectral responses. [10] Carroll et al. [11] also reported an enhanced nonlinear transmittance obtained by a RSA dye blended with carbon nanotubes. Recently, Blau et al. [12] presented a study on nonlinear optical characterization of stable porphyrin/SWNT composite solutions obtained by non-covalent bonding between the carbon nanotubes and conjugated tetraphenylporphyrin molecules. However, little research has been carried out on optical limiting effects of covalently functionalized SWNTs with reverse saturable absorbents. Vivien et al. [5] predicted that further optimizations of the optical limiting performances of carbon nanotubes may be achieved by the cumulative influences of different nonlinear effects arising from functionalized carbon nanotubes with reverse saturable absorbents. Porphyrins are often used as visible chromophores to decorate the surfaces of semiconductor and metal nanoparticles, and they are also promising candidates for applications in optical limiters owing to their large RSA in the visible even near-infrared wavelength range. [13–15] Furthermore, an effective energy or electron transfer may exist in the functionalized SWNTs with porphyrins. [16] The photoinduced electron transfer can result in a large optical limiting effect, which has been observed in the PVK-modified SWNTs system. [17,18] We also reported that a