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 Imχ3 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.
Nikoli et al. (Tue,) studied this question.