Iron Oxide Nanoparticles Labeled with an Excited‐State Intramolecular Proton Transfer Dye

Abstract

Excited-state intramolecular proton transfer (ESIPT) is a particularly well known reaction that has been very little studied in magnetic environments. In this work, we report on the photophysical behavior of a known ESIPT dye of the benzothiazole class, when in solution with uncoated superparamagnetic iron oxide nanoparticles, and when grafted to silica-coated iron oxide nanoparticles. Uncoated iron oxide nanoparticles promoted the fluorescence quenching of the ESIPT dye, resulting from collisions during the lifetime of the excited state. The assembly of iron oxide nanoparticles with a shell of silica provided recovery of the ESIPT emission, due to the isolation promoted by the silica shell. The silica network gives protection against the fluorescence quenching of the dye, allowing the nanoparticles to act as a bimodal (optical and magnetic) imaging contrast agent with a large Stokes shift.

TD-DFT study of the excited state intramolecular proton transfer (ESIPT) mechanism and photophysical properties in coumarin–benzothiazole derivatives: substitution and solvent effects

“…52 Among the most common ESIPT molecules, 2-(2′-hydroxyphenyl)benzothiazole (HBT) (Scheme 1a) has received great interest because of its efficient ESIPT emission and environmentally sensitive spectral properties. [53][54][55][56][57] Padalkar et al have utilized benzothiazole as an electron donating unit to synthesize triphenylamine-benzothiazole luminescent materials with a large Stokes shift (∼15 000 cm −1 ) and very high quantum efficiencies (∼90%). 58 Santos et al investigated the photophysics of three benzothiazole derivatives that exhibit excited state intramolecular proton transfer (ESIPT) in a confined medium afforded by the water-soluble supramolecular host octa acid.…”

Ultrasmall iron oxide nanoparticles functionalized with BODIPY derivatives as potential bimodal probes for MRI and optical imaging

“…By combining iron oxide nanoparticles with an organic luminophore, one can create a bimodal probe which is endowed with very good spatial resolution and high sensitivity. [ 4,13–17 ] Other examples of luminophores that were coupled to iron oxide nanoparticles include quantum dots, [ 18,19 ] gold nanoparticles, [ 20,21 ] dendrimers, [ 22 ] organic fluorophores, [ 23–26 ] and lanthanide complexes. [ 27,28 ] Some of these probes suffer from serious shortcomings that include their low biocompatibility or their large size, which can result in a significant decrease of their retention time in blood.…”