Enhanced Third-Order Nonlinear Optical Properties through Covalent Interfacial Interactions in Defective COF@CNT

Defect engineering enables the composites with favorable covalent interfacial compatibility, which demonstrate considerable promise for third-order nonlinear optical (NLO) applications. In this work, 1,3,5-triformylphloroglucinol (Tp) and five diamines are selected as building blocks for the covalent organic frameworks (COFs), along with R -/ S -1-(1-naphthyl) ethylamine ( R -/ S -NEA) as the modulator, and are reacted with aminated carbon nanotubes (CNTs) to yield the defective COF@CNT (d-COF@CNT). The defect sites result in enhanced interfacial interactions. The d-COF@CNT exhibits the best NLO performance in the near-infrared and the visible-range laser irradiation. Taking d-Bpy-COF@CNT as an example, the reverse saturation absorption (RSA) exhibits 3.16-fold and 1.42-fold enhancements under 1030 nm, respectively. Similarly, the self-focusing properties show 2.34-fold and 1.30-fold improvements. Theoretical calculations and femtosecond transient absorption spectroscopy (fs-TAS) analysis indicate that the superior NLO performance of d-COF@CNT is attributed to the excellent interfacial compatibility, which significantly enhances electron transfer efficiency, thereby improving the NLO performance. This study provides new insights and methods for the design and development of novel third-order NLO composite materials.