Single-Photon Ionization of Organic Molecules Beyond 10 kDa

Abstract

The volatilization and soft ionization of complex neutral macromolecules at low energies has remained an outstanding challenge for several decades [1]. Most volatilization techniques in mass spectrometry produce ions already in the source and most of them lead to particle velocities in excess of several hundred meters per second. For many macromolecules, post-ionization is inefficient since electronic or optical excitations can be followed by competing non-ionizing internal conversion, electron recapture, or fragmentation processes. Here, we explore the laser-assisted volatilization of neutral perfluoroalkyl-functionalized tetraphenylporphyrins as well as their single-photon ionization using vacuum ultraviolet (VUV) light at 157 nm. A systematic investigation of the ionization curves allows us to determine the molecular velocity distribution and ionization cross sections. We demonstrate the detection of single photon ionized intact organic molecules in excess of 10 kDa from a slow molecular beam.

Synthesis of Highly Fluoroalkyl‐Functionalized Oligoporphyrin Systems

“…As shown in Figure 1, up to 60 perfluoroalkyl side‐chains can be connected by substituting the fluorine atoms of both core units. To the best of our knowledge, there has been only one example of a photoionizable fluorinated porphyrin library reported in the literature13 so far. By using 1 and 2 as precursors of libraries, the mass of the library components can be increased.…”

“…Quantum experiments with even larger compounds became possible by attaching fluoroalkyl chains to stable core structures 10,11. Recently, this strategy was successfully applied to components with a molecular weight even beyond 10000 g/mol, selected from a molecular library consisting of porphyrin structures comprising different numbers of fluoroalkylsulfanyl substituents 12,13. In the experimental set‐up, particles with a small mass range were exclusively observed.…”

“…[10,11] Recently, this strategy was successfully applied to components with a molecular weight even beyond 10000 g/mol, selected from a molecular library consisting of porphyrin structures comprising different numbers of fluoroalkylsulfanyl substituents. [12,13] In the experimental set-up, particles with a small mass range were exclusively observed. Therefore libraries composed of particles of different masses are perfectly suitable as long as the particle of these libraries were designed for quantum interference experiments.…”

Isotope-selective high-order interferometry with large organic molecules in free fall

“…We assume that the optical molecular properties do not change as a function of their velocity. While this assumption would not need any explanation for atoms-except for the obvious small Doppler shifts-experiments with nanosecond laser desorption have seen a correlation between internal temperature and kinetic energy [35]. However, in a quasi-thermal long-pulse process as used here, the internal temperature, which defines the spectrum, is expected to be equilibrated and independent of velocity.…”

“…Even for the same chemical sum formula, the library still contains a variety of structural isomers, differing in constitution and conformation. All members of one mass in the family are expected to be very similar in their electrical and optical properties, since all side-chains are identical and electronically only weakly coupled to the porphyrin core which dominates the molecular UV/VIS response and their susceptibility to VUV photoionization [35]. Compounds (1) and (3) differ by an order of magnitude in mass.…”