Issue 12, 2016

Origin of ultraweak fluorescence of 8-hydroxyquinoline in water: photoinduced ultrafast proton transfer

Abstract

8-Hydroxyquinoline (8-HQ), commonly known as oxine, is the most popular among the hydroxyquinolines due to its excellence in complex formation with metal ions and with a wide spectrum of pharmacological applications. 8-HQ and many of its derivatives are fluorogenic ligands when complexed with metal ions. Thus they are regularly used for detection, separation, and quantitative analysis of metal ions as well. For example when chelated with aluminum, the coordinated complex exhibits strong visible emission, which is applicable for the fabrication of organic light-emitting diodes. Although metal complexes with 8-HQ and its derivatives are fluorescent promising wide applications, the ligand itself, 8-HQ, is surprisingly a very weak fluorophore in most of the media, because of its short lifetime in the excited state. To address the nature of ultrashort-lived 8-HQ in the excited sate, we study its photochemical and photophysical processes in acidic, basic, and neutral aqueous media. Our results show that 8-HQ as well as its protonated and deprotonated forms, undergoes ultrafast excited-state proton transfer within femto-to-picoseconds to produce a tautomer as a product, the lifetime of which is also ultrashort. This can give a clue as to why metal complexes of 8-HQ generally show strong fluorescence whereas 8-HQ itself is rarely fluorescent in aqueous solutions; when 8-HQ binds to metal cations, the ligand is in the deprotonated (anionic) form, which cannot undergo the ultrafast proton transfer without generating the short-lived dark product, but survives much longer to tens of nanoseconds to “turn on” fluorescence.

Graphical abstract: Origin of ultraweak fluorescence of 8-hydroxyquinoline in water: photoinduced ultrafast proton transfer

Supplementary files

Article information

Article type
Paper
Submitted
11 Nov 2015
Accepted
12 Jan 2016
First published
15 Jan 2016

RSC Adv., 2016,6, 9812-9821

Origin of ultraweak fluorescence of 8-hydroxyquinoline in water: photoinduced ultrafast proton transfer

S. Park, P. Ghosh, S. O. Park, Y. M. Lee, S. K. Kwak and O. Kwon, RSC Adv., 2016, 6, 9812 DOI: 10.1039/C5RA23802A

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements