Mechanistic Insights into Excited State Intramolecular Proton Transfer in Isolated and Metal Chelated Supramolecular Chemosensors

Tolga N V Karsili, Barbara Marchetti, Michael N R Ashfold

Research output: Contribution to journalArticle (Academic Journal)peer-review

8 Citations (Scopus)
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Abstract

We report a computational study of excited state intramolecular proton transfer in a series of related and progressively more complex organic chromophores ranging from 2-(2′-hydroxyphenyl)-benzoxazole (HBO) through to the 5-(benzo[d]oxazol-2-yl)-2-(4-((bis(pyridin-2-ylmethyl)amino)methyl)benzo[d]oxazol-2-yl)-4 hydroxyphenolate (HDBO′) anion. The latter chelates group 12 metal cations (X = Zn2+, Cd2+ and Hg2+), and can serve as a fluorescence-based sensor for such metals. Initial π* ← π excitation of the ground (S0) state enol-tautomer induces charge separation in the first excited singlet (S1) state and drives the subsequent proton transfer (i.e. enol → keto tautomerism). The keto-tautomer constitutes a local minimum on the S1 PES, and is responsible for highly Stokes shifted fluorescent emission; S1(enol) → S0 fluorescence is proposed to account for the shorter wavelength emission from the X–HDBO′ complexes. Derivatives of HDBO′ that should retain the favourable visible absorption and heavily Stokes shifted emission properties but, additionally, offer higher fluorescence quantum yields (i.e. enhanced metal sensing capability) are proposed.
Original languageEnglish
Pages (from-to)18921-18930
Number of pages10
JournalDalton Transactions
Volume45
Early online date28 Nov 2016
DOIs
Publication statusPublished - 21 Dec 2016

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