“…The FT-IR spectrum of 1 can be readily assigned by direct comparison to 3, which contains vibrations characteristic of the PDI portion of the complex (Figure 4, Table 2), namely, two peaks at 1695 and 1657 cm −1 due to the vibrations of the CO groups and a peak at 1598 cm −1 resulting from various vibrations of the PDI aromatic core, all in excellent agreement with previously reported spectra of the closely related 1,4,5,8-naphthalenediimide 120 and PNI. 114,115 The oscillator strength of the CC bond in 3 is too low to be observed in its FT-IR spectrum in solution. Similarly, 2 exhibits nearly identical infrared-active stretches emanating from the PDI acetylide moiety ( Figure 4, Table 2), including a CC vibration at 2091 cm −1 , two CO bands centered at 1692 and 1655 cm −1 , and delocalized PDI aromatic core vibrations at 1590 cm −1 .…”