Bend, Don't Break: Exploring the Mechanochromic, AIE and Nonlinear Optical Properties of Carbazole-Thiobarbituric Acid Hybrids.

Abstract

To examine the influence of hydrophobic interactions on the nonlinear optical behaviour (NLO), aggregation-induced emission (AIE), mechanofluorochromic (MFC) features of carbazole-thiobarbituric acid (TBA) D-π-A conjugates, we synthesised three different systems with varying alkyl chain lengths. The synthesised conjugates provided clear evidence of intramolecular charge transfer (ICT), which has been investigated through a combination of UV-Vis absorption, fluorescence emission spectroscopy, and theoretical calculations. TBA conjugates exhibited enhanced emission behaviour on aggregation in THF: H2O ratios, reversible MFC and an impressive aggregation-enhanced NLO behaviour. The MFC mechanism was investigated through powder X-ray diffraction (p-XRD) and solid-state emission spectroscopy between grinding and fuming processes. The open-aperture (OA) Z-scan technique, using an Nd: YAG laser (532 nm, 10 Hz, 9 ns), was employed to study NLO absorption. This technique confirmed that all conjugates demonstrated aggregation enhanced two-photon absorption (TPA) and energy-absorbing optical limiting behaviour. The results showed that the alkyl chain length affects the extent of AIE, MFC and NLO properties. These findings highlight the potential for adjusting nonlinearity via molecular arrangement changes in carbazole-thiobarbituric acid-based organic dyes and open new research avenues in this field.