Spectroscopic characterisation of centropolyindanes

A highly promising class of three-dimensional polyaromatic hydrocarbons comprises the centropolyindanes. The characteristic feature of these compounds is the mutual fusion of several molecules of indane along the saturated C-C bonds of their cyclopentane rings. Among the polycyclic aromatic hydrocarbons, the centropolyindanes are special because of the saturated core of sp3-hybridised carbon atoms embedded in a three-dimensional environment of aromatic building blocks. While the centropolyindanes and their numerous derivatives have been studied in detail by NMR spectroscopy, mass spectrometry and X-ray diffraction, investigation of their vibrational features, and especially those of the neopentane core present in most cases, have not been performed so far. In the present paper, we report the first systematic study of a set of centropolyindanes by vibrational spectroscopy, using inelastic neutron scattering (INS), infrared and Raman spectroscopies.


Table of contents
Synthesis of 1,4-dimethoxytriptindane (8).Table S1 Observed and calculated transition energies and assignments for indane (1) in the solid state.
The use of dispersion corrected functionals.General: Melting points were measured with an Electrothermal melting point apparatus and are uncorrected.Nuclear resonance spectra were recorded with a Bruker AC-250 P instrument, using deuterochloroform as a solvent and tetramethylsilane as an internal standard.Infrared spectra were recorded with a Perkin-Elmer model 841 instrument.Mass spectra were recorded with a VG Autospec sector-field instrument; accurate masses were determined with the same instrument using the highvoltage-scan method.Combustion analyses were carried out with a LECO model CHNS-932 instrument (Zentrale Analytik of the Department of Chemistry of Bielefeld University).Column chromatography: silica gel (Kieselgel 60), 0.0630.200mm (Merck); the elution solvents were distilled prior to use.Thinlayer chromatography: silica gel (Kieselgel 60 F 254 ) on Al foil (Merck).

The use of dispersion corrected functionals
Ideally all of the calculations would have been based on experimentally determined crystal structures and with the inclusion of dispersion corrections.This was not done for two reasons: as mentioned in the text and shown in Chart 1, structures are only available for some of the compounds (2, 3, 6, 9), thus to ensure a common approach, all the calculations were for the isolated molecule.We are aware of the limitations of the method and we address this in the first part of the "Comparison of spectra" section, where we compare the results of the isolated molecule and the complete crystal structure calculations (see Fig. 5).The differences are minor, justifying the use of the isolated molecule approach.The crystal structure calculations did not include the dispersion correction, as this was not available in the version of CASTEP used at the time.We have repeated the calculation for tribenzotriquinacene (3) with the Tkatchenko and Scheffler 2 (TS) dispersion correction and, as shown below, the results are very similar to that without the TS correction.There are minor band shifts in the low energy region of the spectrum, but these do not alter the discussion of the spectra.The CASTEP spectrum in Figure 5 includes the TS correction.

Fig. S8
Fig. S8 Comparison of calculated and experimental infrared and INS spectra of triptindane (2).

Fig
Fig. S9 Comparison of calculated and experimental infrared and INS spectra of tribenzotriquinacene (3).

Fig
Fig. S10 Comparison of calculated and experimental infrared and INS spectra of difuso-centrotriindane (4).

Fig. S12
Fig. S12 Comparison of calculated and experimental infrared and INS spectra of fenestrindane (6).
. The numbers in brackets are the phenylene modes in the Wilson notation.b Symmetry label in C s .c s = strong, m = medium, w = weak, v = very, br = broad, sh = shoulder, FR = Fermi resonance

Table S1
Observed and calculated transition energies and assignments for indane(1)in the solid state.The numbering scheme is shown in Table1 a