Excited state dynamics in the matrix‐assisted laser desorption/ionization matrix 2, 4, 6‐trihydroxyacetophenone: Evidence for triplet pooling charge separation reactions. (18th August 2014)

• Record Type: Journal Article
• Authors: Kirmess, Kristopher M.; Knochenmuss, Richard; Blanchard, Gary J.; Kinsel, Gary R.
• Is Part Of: Rapid communications in mass spectrometry. Volume 28:Number 19(2014)
• Page Start: 2134
• Page End: 2140
• Publication Date: 2014-08-18
• Subjects: Mass spectrometry -- Periodicals; 543.65
• DOI: 10.1002/rcm.7000
• Languages: English
• ISSNs: 0951-4198

Abstract

<abstract abstract-type="main"> <title> <x xml:space="preserve">Abstract</x> </title> <sec id="rcm7000-sec-0001" sec-type="section"> <title>RATIONALE</title> <p>Excited state pooling reactions are a central part of some models of ultraviolet matrix‐assisted laser desorption/ionization (MALDI) mechanisms. Evidence has been found for pooling in several matrix materials, but a recent report of pure exponential fluorescence decay at MALDI‐relevant laser fluences suggested that 2, 4, 6‐trihydroxy‐acetophenone (THAP) may be an example of a matrix in which pooling does not occur (Lin <italic>et al</italic>., <italic>Rapid Commun. Mass Spectrom.</italic><bold>2014</bold>, <italic>28</italic>, 77). However, those data were instrumentally limited in dynamic range and signal/noise ratio, and the conclusion does not take into account several aspects of THAP excited state dynamics.</p> </sec> <sec id="rcm7000-sec-0002" sec-type="section"> <title>METHODS</title> <p>Using time‐correlated single photon counting, and absorption and emission spectroscopies, the excited state dynamics of THAP are reexamined.</p> </sec> <sec id="rcm7000-sec-0003" sec-type="section"> <title>RESULTS</title> <p>Like many other aromatic ketones and acetophenone, isolated THAP molecules undergo very efficient intersystem crossing. No fluorescence is observed in dilute solution. In the solid state, efficient fluorescence reappears, but is non‐exponential even at very low excitation intensity. The solvent used for sample preparation was found to have a large effect on the spectra and decay curves. Needle‐like crystals seem to be correlated with reduced intersystem crossing.</p> </sec> <sec id="rcm7000-sec-0004" sec-type="section"> <title>CONCLUSIONS</title> <p>THAP solid state fluorescence is entirely due to intermolecular interactions. Activation of fluorescence, instead of quenching, is a clear indicator of delocalized excited state phenomena in THAP. Contrary to the conclusions of Lin <italic>et al</italic>., the greatly increased singlet lifetime in the solid state substantially increases the probability that pooling‐type reactions are indeed involved in ionization processes. The sensitivity of fluorescence and phosphorescence on sample morphology appears to reflect changes in intermolecular interactions due to crystal packing. Pooling charge separation pathways based on known triplet‐triplet ionization reactions of aromatic ketones are proposed. Copyright © 2014 John Wiley & Sons, Ltd.</p> </sec> </abstract>