  The quantum superposition principle, a key distinction between quantum
physics and classical mechanics, is often perceived as a philosophical
challenge to our concepts of reality, locality or space-time since it contrasts
our intuitive expectations with experimental observations on isolated quantum
systems. While we are used to associating the notion of localization with
massive bodies, quantum physics teaches us that every individual object is
associated with a wave function that may eventually delocalize by far more than
the body's own extension. Numerous experiments have verified this concept at
the microscopic scale but intuition wavers when it comes to delocalization
experiments with complex objects. While quantum science is the uncontested
ideal of a physics theory, one may ask if the superposition principle can
persist on all complexity scales. This motivates matter-wave diffraction and
interference studies with large compounds in a three-grating interferometer
configuration which also necessitates the preparation of high-mass nanoparticle
beams at low velocities. Here we demonstrate how synthetic chemistry allows us
to prepare libraries of fluorous porphyrins which can be tailored to exhibit
high mass, good thermal stability and relatively low polarizability, which
allows us to form slow thermal beams of these high-mass compounds, which can be
detected in electron ionization mass spectrometry. We present successful
superposition experiments with selected species from these molecular libraries
in a quantum interferometer, which utilizes the diffraction of matter waves at
an optical phase grating. We observe high-contrast quantum fringe patterns with
molecules exceeding a mass of 10 000 amu and 810 atoms in a single particle.
