**1. Introduction**

Faraday rotation (FR) is a magneto-optic (MO) effect that was discovered more than a century ago [1]. It is the rotation of the plane of polarization in the presence of a longitudinal magnetic field, and the rotation angle θ can be described by θ = *VBL* with the angle of polarization rotation, V the Verdet constant, *B* the magnetic field parallel to the propagation of light, and *L* the path length. Applications of FR are of practical relevance for magnetic field sensors, wave guiding, fiber-optics, etc. [2–4]. Traditionally the field of magneto-optics has been dominated by inorganic materials or radical species [5–8]. Only recently have diamagnetic organic materials emerged as novel FR supplies [9–14].

Although the exact origin of Faraday rotation in organic molecules is currently unknown, different research groups have dedicated their efforts to designing new organic materials for FR applications. Current experiments reported in the literature clearly suggest that molecular conjugation and π-stacking are crucial factors to obtain very strong FR. Furthermore, for organic diamagnetic materials, it became evident that the macroscopic order of the bulk material is crucial for its optical and MO activity [9–14]. It is this duality of molecular vs. macroscopic material, i.e., intra- vs. intermolecular processes, that complicates a rational correlation of the observed magnetic effects with the nature of molecular units and supramolecular aggregates**.** We have recently shown how the structural simplification of the molecular units (from trigonal to linear) has led to an increase in the FR activity of the respective thin-film materials [15]. Nonetheless, one has to keep in mind the macroscopic structure of the respective aggregates. A decisive requirement is the capacity to form quality thin films from molecular units or aggregates, either crystalline [16] or liquid crystalline [17]. It was shown that long-range electron movement along columnar supramolecular aggregates leads to a dramatically increased Faraday response [18].
