Abstract
Photoinduced electron transfer (PET), which causes pH-dependent quenching of fluorescent dyes, is more effectively introduced by phenolic groups than by amino groups which have been much more commonly used so far. That is demonstrated by fluorescence measurements involving several classes of fluorophores. Electrochemical measurements show that PET in several amino-modified dyes is thermodynamically favorable, even though it was not experimentally found, underlining the importance of kinetic aspects to the process. Consequently, the attachment of phenolic groups allows for fast and simple preparation of a wide selection of fluorescent pH-probes with tailor-made spectral properties, sensitive ranges, and individual advantages, so that a large number of applications can be realized. Fluorophores carrying phenolic groups may also be used for sensing analytes other than pH or molecular switching and signaling.
Highlights
For the first time, a comparison between fluorescent pH-probes carrying phenolic Photoinduced electron transfer (PET) groups and those bearing amines on the basis of various fluorophores
Only a few examples of pH-probes carrying phenolic Photoinduced electron transfer (PET) groups have been presented, most of which are BODIPY dyes.[22−27] On the other hand, in many fluorescent pH-probes, phenolic groups are fully integrated into the chromophore, for instance in fluoresceins
Quenching caused by PET at basic pH was significantly stronger for the dyes carrying phenolic groups than for those bearing amines
Summary
For the first time, a comparison between fluorescent pH-probes carrying phenolic PET groups and those bearing amines on the basis of various fluorophores. Several dye classes with very different spectral and structural properties (Figures 1 and 2 and Table 1) have been selected for this work, including xanthenes (fluoresceins and sulforhodamines), diketopyrrolo[3,4-c]pyrroles (DPPs), and perylene bisimides (PBIs). Quenching caused by PET at basic pH was significantly stronger for the dyes carrying phenolic groups (dyes 1−6 A,B) than for those bearing amines (dyes 1−6 C,D)
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