Squaramide—Naphthalimide Conjugates as “Turn-On” Fluorescent Sensors for Bromide Through an Aggregation-Disaggregation Approach

Abstract

The syntheses of two new squaramide-naphthalimide conjugates ( SQ1 and SQ2 ) are reported where both compounds have been shown to act as selective fluorescence “turn on” probes for bromide in aqueous DMSO solution through a disaggregation induced response. SQ1 and SQ2 displayed a large degree of self-aggregation in aqueous solution that is disrupted at increased temperature as studied by 1 H NMR and Scanning Electron Microscopy (SEM). Moreover, the fluorescence behavior of both receptors was shown to be highly dependent upon the aggregation state and increasing temperature gave rise to a significant increase in fluorescence intensity. Moreover, this disaggregation induced emission (DIE) response was exploited for the selective recognition of certain halides, where the receptors gave rise to distinct responses related to the interaction of the various halide anions with the receptors. Addition of F − rendered both compounds non-emissive; thought to be due to a deprotonation event while, surprisingly, Br − resulted in a dramatic 500–600% fluorescence enhancement thought to be due to a disruption of compound aggregation and allowing the monomeric receptors to dominate in solution. Furthermore, optical sensing parameters such as limits of detection and binding constant of probes were also measured toward the various halides (F − , Cl − , Br − , and I − ) where both SQ1 and SQ2 were found to sense halides with adequate sensitivity to measure μM levels of halide contamination. Finally, initial studies in a human cell line were also conducted where it was observed that both compounds are capable of being taken up by HeLa cells, exhibiting intracellular fluorescence as measured by both confocal microscopy and flow cytometry. Finally, using flow cytometry we were also able to show that cells treated with NaBr exhibited a demonstrable spectroscopic response when treated with either SQ1 or SQ2 .

Squaramide‐Based Self‐Associating Amphiphiles for Anion Recognition

“…Related work has also shown that di‐aryl ureas can form extended hydrogen bonding and π‐π interactions in the solid state, to produce supramolecular gels with antimicrobial properties against Staphylococcus aureus and Escherichia coli [20] . Our interest in SSAs stems from our recent report on squaramide‐naphthalimide conjugates that display self‐association characteristics [21] . Using this approach we were able to effectively disrupt self‐association bringing about a disaggregation induced emission response in the presence of halide anions.…”

“… [20] Our interest in SSAs stems from our recent report on squaramide‐naphthalimide conjugates that display self‐association characteristics. [21] Using this approach we were able to effectively disrupt self‐association bringing about a disaggregation induced emission response in the presence of halide anions. In particular, we discovered that the squaramide‐naphthalimide conjugates exhibited distinct responses with each halide, in the case of Br − resulting in a dramatic 500–600 % fluorescence enhancement.…”

Supramolecular Polymers With AIE Property Fabricated From a Cyanostilbene Motif-Derived Ditopic Benzo-21-Crown-7 and a Ditopic Dialkylammonium Salt

“…The driving force of supramolecular polymers usually includes hydrogen bonds (Xiao et al, 2019b , e ; Datta et al, 2020 ; Qi et al, 2020 ), metal-ligand bonds (Zheng et al, 2016 ; Shi et al, 2019 ), host-guest complexation (Guo et al, 2010 ; Harada et al, 2014 ; Wang et al, 2018 ; Xiao and Wang, 2018 ; Xiao et al, 2018 , 2019d ; Chen et al, 2019 ), donor–acceptor interaction (Han et al, 2018 ), π-π stacking (Wagner et al, 2019 ; Xiao et al, 2019c ), or a combination of them (Li et al, 2012 ; Wei et al, 2015 ; Xiao et al, 2020b ). In recent years, supramolecular fluorescent materials have drawn much attention, such as fluorescent molecular switches (Cheng et al, 2017 ), fluorescent sensors (Kumawat et al, 2019 ), fluorescent metallaclip (Wang et al, 2019 ), and artificial light-harvesting systems (Xiao et al, 2019g , 2020a ). Particularly, the development of fluorescent supramolecular polymers (FSPs) has attracted more and more interest because of their potential application in the area of dynamic luminescent materials (Ji et al, 2013 ; Zhang et al, 2017 , 2018 ; Li et al, 2019 ).…”

Unusual redshift due to selective hydrogen bonding between F− ion and sensor motif: a naked eye colorimetric sensor for F− ions in an aqueous environment

“…[27][28][29][30][31][32][33][34] Many of the above-mentioned systems can undergo abstraction of a proton by the classical Bronsted acid-base type of interaction at a higher concentration of F À ions. [34][35][36][37][38][39][40][41][42] All the above monomeric systems can detect the analyte at the ppm level through a change in the spectroscopic behavior at a particular wavelength. Among the reported F À ion sensors, very few systems have a ratiometric sensing property, which depends on various factors like concentration, electronic environment, phototransformation, etc.…”

“…6 and 7). 39 Also, in the presence of two 2,4-DNPH groups, a nice cavity was produced by the sensor molecules for F À ions only (as an acetate anion does not interfere with the F À ion). So, it can be concluded that both the species ([sensors + F À ion] and [sensors] 2À ) were present in the solution for all the sensors (compound 4, compound 9, and compound 11).…”