Nonlinear optical response of some perylene diimides (PDIs) and two-dimensional (2D) MoS2-PDI hybrid materials under ns and fs laser excitation
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Date
2026-02-12
Authors
Πραματιώτη, Ευφροσύνη
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Abstract
In the present work, the nonlinear optical response of five perylene diimides (PDIs)—i.e., chemically modified perylenes with phenoxy-azobenzene, aminophenyl, aminophenoxy, and amino groups attached to the bay- and imide-positions of the perylene—was studied, as well as that of two-dimensional semiconducting MoS2 nanosheets bearing the aforementioned perylene diimides. The study of the nonlinear optical response of all the above systems was carried out under different laser excitation conditions, using various excitation wavelengths and pulse durations (4 ns/1064 and 532 nm, 70 fs/800 and 400 nm) and the Z-Scan technique. The aim of the work was the selective modification of the linear and nonlinear optical properties of the semiconducting 2D MoS2 structures for various photonic and optoelectronic applications (e.g., optical switches, optical gates, optical limiters, development of dyes for mode-locking, etc.) A noticeable tune of the NLO character between the PDI derivatives was observed, revealing the importance of the functionalization of the PDI core by the anchored electron donating units. The largest NLO value was achieved by the incorporation of p-aminoazobenzene at the PDI bay position.The mechanism which could lead to an efficient tune of the PDIs NLO response, is associated with the modification of their electronic character resulting by the proper PDI core functionalization. The hybrids exhibit enhanced and tunable NLO absorptive (switching from saturable to reverse saturable absorption with intensity) and 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 excitation. Hybrids demonstrate superior NLO susceptibility (χ³) values, particularly under resonant 532 nm excitation, with Im{χ³} up to -514.7 ± 57.4 × 10-13 esu·mL/mg for 2a at low intensity, 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, modelocking, and photonic devices. Threshold intensities for NLA switching (150-250 MW/cm²) exceed those of MoS2, highlighting stability for high-power uses. The newly developed hybrid materials advance two-dimensional transition metal dichalcogenidebased optoelectronics by overcoming light-matter interaction limits through molecular antenna effects from PDIs. The study underscores substituent position and azobenzene integration as levers for NLO optimization in hybrid nanoarchitectures.
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Nonlinear optics, Photonics, 2D materials