Heterocyclic biphenyl based fluorochrome sensor for rapid hydrazine detection: Design, synthesis, single crystal XRD and DFT studies

Abstract

In our continuous research focused on enhancing sensing technologies, this article presents a series of groundbreaking fluorochromes that feature a biphenyle scaffold. A novel fluorochrome sensors are developed with various heterocycle aldehydes by Claisen-Schmidt condensation. This condensation is performed by use of KOH and pyrrolidine as a catalyst to provide two different methods with compatative studies. The attained results show KOH as a speedy catalyst (2-3 hrs; 71-80 %) however pyrrolidine as an effective catalyst (5-6 hrs; 85-95 %). Structures of prepared fluorochrome are characterized by various spectral techniques and single crystal XRD. Photo physical properties of these fluorochromes are investigated by UV-Vis and Fluorescence spectrophotometer with different solvent systems. DFT calculations are observed to have a good correlation with experimental results. Obtained results of absorption, photoluminescence and their theoretical correlation suggest that the prepared fluorochrome can be optimized for their applications in optoelectronics, sensing, and bioimaging. Fluorochrome 3g with the highest Stoke’s shift (129 nm) and photoluminescence nature (QY 0.87) is used to demonstrate the detection of hydrazine in actual water, soil and air samples. Fluorochrome themself are color compounds and exhibits a good photo luminesce, which significantly gets quenched when hydrazine is added in very small quantity. Disappearance of color and quenching of photo luminesce signal is attributed to the formation of hydrodiazole by cyclization with hydrazine. A very good linear relationship for the detection of hydrazine is observed with the concentration range of 1–5 μM in methanol. The limit of detection (LOD) for hydrazine is observed 1.1 μM with 5 μM 3g. Moreover, the color change of fluorochrome solution from yellow to colorless is able to observed by naked eye, showing these fluorochrome can also be used as a colorimetric sensor for hydrazine at very low concentration. Real time detection ability of fluorochrome 3g is investigated in different working pH range (4-10), selective detection among interfering analytes, soil and water sample with great efficiency. Probable mechanism for the detection of hydrazine is also established by spectral study. Additionally this study offers straightforward cost-effective probe-coated paper sheet for the detection of hydrazine in environment and giving further hope for its commercial applications.