Exploring two-photon absorption and optical limiting properties of melt-grown 2,4-dinitroaniline (DNAN) single crystal under nanosecond pulsed laser excitation

Abstract

An organic nonlinear optical single crystal of 2,4-dinitroaniline (DNAN) was successfully grown using the vertical Bridgman method for the first time. Differential thermal analysis revealed that DNAN has a melting point of 180 °C and a freezing point of 170 °C, indicating its thermal phase transition behavior. Single crystal X-ray diffraction analysis confirmed that the title compound crystallizes in the monoclinic system with space group P2_1/c. FT-Raman spectroscopy confirmed the retention of DNAN’s functional groups during the melt-to-crystal transformation. TG-DTA revealed that DNAN is thermally stable up to 190 °C and decomposition occurring at 300 °C. Vickers microhardness testing revealed good mechanical stability of DNAN exhibiting a reverse size indentation effect and classifying it as a soft material based on Mayer’s plot. Photoconductivity studies demonstrated that DNAN exhibits negative photoconductivity with ohmic behavior. UV-visible analysis revealed 60% transmittance in the 500-1000 nm range, with a cut-off wavelength at 486 nm. The optical band gap was determined to be 2.52 eV using Tauc’s plot. Photoluminescence analysis showed fluorescence emission at 513 nm under 350 nm excitation. Z-scan analysis using a 9 ns pulsed Nd:YAG laser at 532 nm revealed reverse saturation absorption. The material exhibited a nonlinear absorption coefficient of 1.38 × 10^–10 m/W and an optical limiting threshold of 2.24 GW/m², confirming its potential for optical limiting applications. Hirshfeld surface mapping highlighted intermolecular interactions contributing to nonlinearity and crystal stability. The 2D fingerprint plots revealed that O-H interactions (41.3%) are the most significant contributors to crystal packing.