Solvatochromism and halochromism in nitro lophine derivatives: Photophysical study, computational calculations and applications as pH sensing material

Abstract

Nitro Lophines were readily synthesized via multicomponent reaction of benzil, nitro benzaldehyde and ammonium acetate. All three nitro Lophines were isolated in good yields and were also characterized by various analytical and spectroscopic techniques. A distinctive solvatochromism was observed in case of ortho and para nitro containing Lophines in their absorbance spectra. In particular, naked eye solvatochromism was observed, in case of para nitro Lophine, in the form of yellow and red coloured solution in methanol and DMSO respectively. Halochromism studies revealed the hypsochromic shift under acidic pH while bathochromic shift under alkaline pH for both nitro Lophines. Again the para nitro Lophine demonstrated wonderful distinctive colour change under acidic and alkaline pH in both methanol and DMSO as solvents. The measurement of absorbance at different pH values was carried out and the data obtained were used for calculation of dissociation constants employing several graphical methods. Computational calculations were carried out using TD-DFT for UV–Vis absorption calculation while graph-convolutional neural network model was utilized for calculation of dissociation constants. Ultimately, a reusable naked eye pH detection paper could be developed using para nitro Lophine as a sole indicator.