Tuning the Nonlinear Optical Properties of MoS2 by Interfacing with Bay- or Imide-Substituted Perylene Diimides

Abstract

We have investigated the tuning of nonlinear optical (NLO) properties in semiconducting MoS2 nanosheets through covalent functionalization with bay- or imide-substituted perylene diimide (PDI) derivatives. Five MoS2−PDI hybrid nanomaterials 1a−5a were synthesized by attaching PDI variants featuring azobenzene or other substituents, characterized via Raman, IR, TGA, STEM-EDS, ultraviolet−visible (UV−vis), photoluminescence, and electrochemical analyses, and evaluated for NLO response under nanosecond (4 ns, 1064/532 nm) and femtosecond (70 fs, 800/400 nm) laser excitations. The hybrids exhibit enhanced and tunable NLO-absorptive (switching from saturable to reverse-saturable absorption with intensity) and NLO-refractive (self-focusing) responses compared to exfoliated MoS2, with 1a and 2a (azobenzene-substituted PDIs) showing the strongest effects due to efficient electron-transfer and -resonant excitations. Hybrids demonstrate superior NLO susceptibility (χ3) values, particularly under resonant 532 nm excitation, with Im{χ3} values of up to −514.7 ± 57.4 × 10−13 esu·mL/mg for 2a at low intensities, attributed to Pauli blocking, defect states, and two-photon processes. Hybrids having bay-substituted PDIs grafted on MoS2 enhance conjugation and performance over imide variants, enabling applications in optical-limiting, mode-locking, and photonic devices. Threshold intensities for NLA switching (150−250 MW/cm2) exceed those of MoS2, highlighting the stability for high-power uses. The developed hybrid materials advance two-dimensional transition-metal dichalcogenide-based optoelectronics by overcoming light−matter interaction limits through molecular antenna effects from PDIs. The study underscores the substituent position and azobenzene integration as levers for NLO optimization in hybrid nanoarchitectures.