Green to red emitting BODIPY dyes for fluorescent sensing and imaging of carbon dioxide

Several new BODIPY pH indicators are prepared and tested as transducers in polymer-based optical carbon dioxide sensors. Apart from classical BODIPY chromophore absorbing at around 505 nm, π-extended analogs showing absorption maxima at around 635 and 665 nm are prepared. All the dyes possess excellent brightness due to combination of high molar absorption coefficients and fluorescence quantum yields. Additionally, the π-extended BODIPYs show unmatched photostability whereas the classical 1,3,5,7-tetramethyl-8-aryl-4,4-difluoroboradiazaindacene is found to be photolabile. The phenol receptors render BODIPY dyes pH sensitive inducing fluorescence quenching in the phenolate form. Carbon dioxide sensors are prepared via immobilization of the dyes into ethyl cellulose along with tetraoctylammonium hydrogencarbonate. The sensitivity of these sensors is mainly guided by the nature of the receptor and to a smaller extent by the nature of the chromophore, and can be tuned over a very wide range covering all important applications. Introduction of the receptor bearing carboxylic group in the o-position towards OH group of the receptor enables highly sensitive sensors resolving ambient CO₂ levels (LOD 0.009 hPa). Sensors based on other indicators show optimal response from 0.2 to 60 hPa and from 20 to 400 hPa, making them attractive for medical and food packaging applications, respectively. Materials for referenced sensing with phase fluorometry and ratiometric imaging with RGB cameras have also been prepared.