Laser-induced acoustic desorption
(LIAD) has recently been established
as a tool for analytical chemistry. It is capable of launching intact,
neutral, or low charged molecules into a high vacuum environment.
This makes it ideally suited to mass spectrometry. LIAD can be used
with fragile biomolecules and very massive compounds alike. Here,
we apply LIAD time-of-flight mass spectrometry (TOF-MS) to the natural
biochromophores chlorophyll, hemin, bilirubin, and biliverdin and
to high mass fluoroalkyl-functionalized porphyrins. We characterize
the variation in the molecular fragmentation patterns as a function
of the desorption and the VUV postionization laser intensity. We find
that LIAD can produce molecular beams an order of magnitude slower
than matrix-assisted laser desorption (MALD), although this depends
on the substrate material. Using titanium foils we observe a most
probable velocity of 20 m/s for functionalized molecules with a mass m = 10 000 Da.
Four different multiporphyrin systems have been synthesized and characterized. Highly fluoroalkyl‐functionalized porphyrins are the most complex objects so far to have exhibited quantum wave nature. We have functionalized larger oligoporphyrin systems with fluoroalkyl chains to increase their mass and minimize their intermolecular interactions. The to‐some‐extent random substitution of fluorine atoms at the periphery of the oligoporphyrins results in libraries consisting of molecules varying in both the number and spatial distribution of substituents. The mass‐selected individual members of these libraries were designed for quantum interference experiments. To investigate the volatilization nature of the molecules within the library, laser desorption and post‐ionization studies were performed. These studies demonstrated that molecular beams of suitable velocity and ionization cross‐section can be obtained from these libraries. In particular, we present these features for two libraries, based on either a tetrahedrally arranged central porphyrin tetramer or a more planar porphyrin pentamer.
Recent progress in synthetic chemistry and molecular quantum optics has enabled demonstrations of the quantum mechanical wave–particle duality for complex particles, with masses exceeding 10 kDa. Future experiments with even larger objects will require new optical preparation and manipulation methods that shall profit from the possibility to cleave a well-defined molecular tag from a larger parent molecule. Here we present the design and synthesis of two model compounds as well as evidence for the photoinduced beam depletion in high vacuum in one case.
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