Edge chlorination of hexa-peri-hexabenzocoronene investigated by density functional theory and vibrational spectroscopy† †Electronic supplementary information (ESI) available: Description and animations of the vibrational normal modes of HBC and HBC-Cl discussed in the text. See DOI: 10.1039/c5cp077

The molecular structure and vibrational properties of perchlorinated HBC and the parent HBC have been investigated by density functional theory calculations and vibrational spectroscopy.


S1.1 Description of normal modes of HBC and HBC-Cl relevant for IR
We follow here the notation of the experimental features given in Figure 7 of the main text.

HBC-Cl
• 1 is assigned to a degenerate pair of collective out-of-plane bending modes of the aromatic core; considering a given ring of the core, these modes involve the six carbon atoms with an alternated pattern of up/down displacements.
• 2 is assigned to a doubly degenerate mode involving the out-of-phase C-Cl stretching of the bonds at 1 and 3 (see Figure 2 of the main text) of the chlorinated aryl moieties.
• 3 is assigned to a collective ring-breathing mode of the aromatic core; this occurs with an alternating pattern and mainly involves the six outer Clar rings of HBC-Cl.
• 4 is assigned to a doubly degenerate mode which mainly involves the in-phase C-Cl stretching of the bonds at 1 and 3 (see Figure 2 of the main text) of the chlorinated aryl moieties.
• 5 is assigned to a doubly degenerate mode which mainly involves the CC stretching of the bonds which could be thought to form the edge of a coronene moiety inscribed in HBC-Cl aromatic core (i.e., bonds of kind c and d in Figure 6 of the main text).
• 6 is assigned to two closely located degenerate modes, computed at 1308 cm -1 and 1316 cm -1 . In both cases the pattern of nuclear displacements is complex and mainly involves the CC bonds of the aromatic core.
• 7 is assigned to the in-phase stretching of the three C-Cl bonds of each chlorinated aryl moiety; the pattern of the mode alternates along HBC-Cl edge (i.e., three aryl moieties have shrinking C-Cl bonds while the other three have stretching C-Cl bonds).
• 8 is assigned to two closely located modes (1463 cm -1 , E u and 1475 cm -1 , A 2u ). The two peaks are not well resolved and appear as a structured feature both in the experimental and simulated spectrum. The E u normal modes collectively involve CC bonds of the aromatic core; the A 2u mode displays a more recognizable pattern, with bonds of kind e (see Figure 6 of the main text) which alternatively stretch in an out-of-phase fashion.
• 9 is assigned to a collective doubly degenerate ring stretching vibration (computed at 1583 cm -1 ), whose pattern is close to that found in discussing the G line in Raman spectroscopy of PAHs. [1] HBC • 1 is assigned to an alternated out-of-plane bending vibration of the carbon atoms in the aromatic core, coupled with the in-phase out-of-plane bending of the CH bonds at 1,3 (see Figure 2 of the main text).
• 2 is assigned to the collective out-of-plane bending of all CH bonds and correlates with the characteristic TRIO features of PAHs. [2,3,4] • 3 is a degenerate doublet involving a collective ring-breathing of the six outer Clar rings of HBC, with half the molecule vibrating out-of-phase with respect to the other half.
• 4,5,6,7,8 are assigned to degenerate modes involving CC stretching of the aromatic core, coupled with in-plane CH bending.
• 9 is assigned to collective doubly degenerate ring stretching vibrations, whose pattern is close to that found in discussing the G line in Raman spectroscopy of PAHs. [1]

S1.2 Description of the normal modes of HBC and HBC-Cl relevant for Raman
We follow here the notation of the experimental features given in Figure 8 of the main text.

S1.2 Raman B modes
• Peak B 1 is assigned to the ring-breathing mode of the central Clar ring of HBC and HBC-Cl which vibrates out-of-phase with respect to the six outer Clar rings. In HBC-Cl mode B 1 is coupled with the collective C-Cl stretching of the chlorinated aryl moieties. In particular C-Cl stretching at (1, 3) (see Figure 2 of the main text) are both out-of-phase with respect to C-Cl stretching at 2 (see Figure 2 of the main text). Compared to HBC, this mode is remarkably blue-shifted in HBC-Cl (experimentally by 79 cm -1 , while according to DFT by 73 cm -1 ).
• Feature B 2 is only found in the HBC-Cl molecule and it is assigned to a doubly degenerate mode which involves the CC stretching of the outer part of the molecule (mainly bonds of kind c and d, see Figure 6 of the main text) coupled with the C-Cl stretching of the chlorinated aryl moieties.

S1.2 Raman D and G modes
Figure S1.2 nuclear displacements of the D and G modes of HBC and HBC-Cl discussed here.
• The weak Raman active doubly degenerate mode D 1 is assigned to a vibration which involves the breathing of four Clar rings in both HBC and HBC-Cl. In HBC-Cl the D 1 mode is coupled with the inphase C-Cl stretching of the chlorinated aryl moieties. In HBC the D 1 mode is coupled with the collective in-plane bending of the CH bonds at positions (1,3) (see Figure 2 of the main text).
• The experimental G 1 feature of HBC and HBC-Cl (see Figure 8 of the main text) is assigned to doubly degenerate modes of E species which mainly involve the CC stretching of bonds in the center of the molecule. In HBC the mode G 1 is coupled with collective in-plane CH bending.
• Feature G 2 is assigned to a totally symmetric mode which involves CC stretching (i.e., ring stretching -see above) mainly at the outer rings of the molecule (bonds of kind b in Figure 6 pf the main text). In HBC the mode G 2 is coupled with collective in-plane CH bending at positions (1,3) (see Figure 2 of the main text). In HBC-Cl the G 2 mode involves the collective C-Cl stretching of bonds at 2 (see Figure 2 of the main text) and it is significantly red-shifted compared to HBC (according to DFT by 103 cm -1 ; the experimental determination of the position of G 2 for HBC is not feasible because it is a weak mode overlapped with other stronger G components).