Highly Photostable Near-Infrared Fluorescent pH Indicators and Sensors Based on BF₂-Chelated Tetraarylazadipyrromethene Dyes

Abstract

In this study, a series of new BF2-chelated tetraarylazadipyrromethane dyes are synthesized and are shown to be suitable for the preparation of on/off photoinduced electron transfer modulated fluorescent sensors. The new indicators are noncovalently entrapped in polyurethane hydrogel D4 and feature absorption maxima in the range 660–710 nm and fluorescence emission maxima at 680–740 nm. Indicators have high molar absorption coefficients of ∼80 000 M–1 cm–1, good quantum yields (up to 20%), excellent photostability and low cross-sensitivity to the ionic strength. pKa values of indicators are determined from absorbance and fluorescence measurements and range from 7 to 11, depending on the substitution pattern of electron-donating and -withdrawing functionalities. Therefore, the new indicators are suitable for exploitation and adaptation in a diverse range of analytical applications. Apparent pKa values in sensor films derived from fluorescence data show 0.5–1 pH units lower values in comparison with those derived from the absorption data due to Förster resonance energy transfer from protonated to deprotonated form. A dual-lifetime referenced sensor is prepared, and application for monitoring of pH in corals is demonstrated.

Solid-state oxygen sensors based on phosphorescent diiodo-borondipyrromethene dye

“…Boron difluoro dipyrromethene (BODIPY) [29] derivatives represent an important class of organic chromophores that have been widely investigated as chemosensors [30][31][32], laser dyes [33], in biological imaging [34], due to their excellent photophysical properties such as high extinction coefficient, high quantum yield of fluorescence, sharp absorption and emission bands as well as excellent photo and chemical stability. Additionally, the electron-rich BODIPY core also allows facile synthetic modification to tune the absorption, emission properties.…”

Hydroxylated near-infrared BODIPY fluorophores as intracellular pH sensors

“…This conjugation can be caused by hydrogen–halogen bonding interactions between the fluorine atom and the hydrogen atom located in the o -position of Ar 3 and Ar 4 rings. 18 Interestingly, the hydroxyl groups in the p -position of the Ar 3 and Ar 4 rings result in the bathochromic shift of the absorption and fluorescence spectra more than their effect if located in the Ar 1 and Ar 2 rings.…”

“…14 Several aza-BODIPY dye fluorescent pH indicators bearing amino- or hydroxy-functionalized substituents were reported by O'Shea and Klimant, respectively. 15–18 …”

Tailoring colour changes of optical sensor materials by combining indicator and inert dyes and their use in sensor layers, textiles and non-wovens

“…the substituents ortho to the hydroxyl group, pH indicators with comparable colour change but different pK a value can be obtained (GJM-492: pK a of 6.1, GJM-503: pK a of 7.7). This generic approach of tailoring pK a has been introduced by Hisamoto et al [15] and has now successfully been adopted by others [16].…”