Phosphate and Water Sensing with a Zinc‐Dipicolylamine‐Based Charge‐Transfer Dye

Abstract

A D‐π‐A (donor‐π bridge‐acceptor) dye with a conjugated dipicolylamine group as the donor was synthesized and characterized. When zinc is bound to the dipicolylamine ligand, charge transfer strength from the donor is decreased resulting in a large blue‐shift in the absorption spectrum with a quenching of dye emission. Upon addition of phosphate, changes in both the absorption and emission spectrum are observed with intermediate states between the starting zinc complex and free dye observed. The zinc‐dye complex was found to react with two equivalents of phosphate or trace water to give the free dye. The water response is unexpected given the widespread use of the dipicolylamine group as an anion sensor in water. When the dipicolylamine group is part of conjugated D‐π‐A dye designs with zinc complexes, the dye is observed to act as a humidity sensor at low water amounts.

Water-Soluble NIR Absorbing and Emitting Indolizine Cyanine and Indolizine Squaraine Dyes for Biological Imaging

“…Dimethyl sulfoxide (DMSO) and MeOH were also selected as solvents, which allows for the comparison of SO 3 C5 and SO 3 SQ to the previously reported dyes C5 and SQ, respectively (see Table S3 for solubility data). 29,30 H 2 O and fetal bovine serum (FBS) were selected as well due to the biological relevance and for a convenient analysis of how these dyes will behave with biological matrix elements in place, as has been previously reported in the literature. 4,33,34 The absorption profiles of both dyes in DMSO and MeOH are not significantly changed relative to the previously published dyes with no sulfonate groups.…”

“…The target sulfonate indolizine cyanine dye (SO 3 C5) is synthesized by reacting 3 with the methine bridge linker 4 in the presence of perchloric acid and acetic anhydride at room temperature similar to previously reported conditions in the literature. 30 The target sulfonate indolizine squaraine (SO 3 SQ) is synthesized via an electrophilic aromatic substitution/ condensation reaction between sulfonate indolizine 3 and squaric acid (5). Importantly, during optimization of the condensation reaction, it was found that the addition of small amounts of water led to an increase in product formation.…”

“…29 To deepen the NIR absorbing properties of these dye classes, designs capable of extending the π-system through a conjugated donor (such as indolizine) are attractive. [29][30][31][32] Recent photophysical studies using proaromatic indolizine donors in place of indoline donors show red-shifting of the absorption and emission profiles of these dyes firmly into the therapeutic window in nonaqueous environments (C5 and SQ compared to ICG and indoline squaraine, respectively; Figure 1). [29][30][31][32] These studies indicated that in the case of phenyl-indolizine derivatives, the phenyl group does not play a significant role in tuning the absorption or emission energy values of the NIR indolizine dyes.…”

“…[29][30][31][32] Recent photophysical studies using proaromatic indolizine donors in place of indoline donors show red-shifting of the absorption and emission profiles of these dyes firmly into the therapeutic window in nonaqueous environments (C5 and SQ compared to ICG and indoline squaraine, respectively; Figure 1). [29][30][31][32] These studies indicated that in the case of phenyl-indolizine derivatives, the phenyl group does not play a significant role in tuning the absorption or emission energy values of the NIR indolizine dyes. 29,30 This enables the use of the phenyl group to append water-soluble functionality without perturbing the core chromophore properties of the dyes, permitting the probing of the photophysical properties of the dyes in aqueous environments.…”

“…[29][30][31][32] These studies indicated that in the case of phenyl-indolizine derivatives, the phenyl group does not play a significant role in tuning the absorption or emission energy values of the NIR indolizine dyes. 29,30 This enables the use of the phenyl group to append water-soluble functionality without perturbing the core chromophore properties of the dyes, permitting the probing of the photophysical properties of the dyes in aqueous environments. Sulfonate-substituted dyes, SO 3 C5 and SO 3 SQ, were targeted given the water-solubilizing properties of sulfonate groups and FDA approval for human use by way of ICG ( Figure 1).…”