11 Starting from a sandwich (a) or brickwork (b) structure relative stable dimer configurations evolved. The figure shows representative snapshots. The experimental absorption spectrum 4 of monomeric PIC (dots) is compared with a calculated spectrum (full line) from the displaced oscillator model. The calculated spectrum was shifted to reproduce the absorption maximum at 19100 cm − 1 The atom numbering for PIC is shown as it is used to tabulate the parameters sandwich brickwork excitation energy E$_{a}$ 2 . 522 ± 0 . 014 eV 2 . 565 ± 0 . 010 eV excitation energy E$_{b}$ 2 . 523 ± 0 . 014 eV 2 . 561 ± 0 . 010 eV excitonic coupling V$_{exc}$ 0 . 25 ± 0 . 017 eV − 0 . 064 ± 0 . 008 eV center-center distance R$_{ab}$ 4 . 25 ± 0 . 08 Å 8 . 33 ± 0 . 24 Å angle between long axes 6 . 0 ± 1 . 7 o 34 . 0 ± 4 . 0 o angle between short axes 174 . 0 ± 2 . 6 o 122 . 0 ± 3 . 9 o distance of charge centers R$_{cc}$ 5 . 42 Å 7 . 57 Å Table II: V. FIGURE CAPTIONS: Figure 1: Figure 2: Figure 3: