Old Dog, New Trick: Discovery of the Solid-State Phthalate Detection Capabilities of Fluorescein.

Abstract

This manuscript presents the development of fluorescent materials capable of detecting di-(2-ethylhexyl) phthalate (DEHP) vapors, which is an important concern for the airspace industry, as during the preparation and on-orbit life of satellites and other spacecraft, phthalate vapors deposit on sensitive optical systems, hampering their proper functioning. Here we present a novel approach for the detection of this contaminant, with a rational design of the materials supported by DFT computations. Our main approach involved the solid-state optical detection of DEHP via photoinduced electron transfer, as a novel phthalate detection strategy. While the pursued response was gratifyingly observed for most of the investigated fluorophores, the detection capabilities of materials containing fluorescein were discovered to be unique, significantly outperforming the other fluorophores. Furthermore, an unanticipated solid-state ratiometric response towards DEHP was observed for fluorescein, displaying a particularly high contrast that allowed a naked-eye detection of the contaminant. The molecular mechanism behind the unique response of fluorescein was investigated in detail both experimentally and theoretically, allowing us to propose a detection mechanism for fluorescein through a DEHP-induced tautomerization between the zwitterionic and the lactoid tautomer of the fluorophore.