Fig. 8. (Color online) Molecular structure and infrared transmittance of bis-MSB. The center of the figure displays the 3D structure of bis-MSB, highlighting its central benzene ring linked at the 1,4 positions to two 2-methylstyryl groups, each containing a benzene ring with a methyl group attached to a vinyl group (C=C). The red (black) solid line represents the infrared transmission spectrum from AIST SDBS sample (our bis-MSB powder sample), while the green line shows the B3LYP DFT calculations performed using Gaussian 16. Despite differences in peak intensity, good alignment in peak positions from two experiments is observed. However, some discrepancies between theoretical calculation and experimental results appear below 1500 cm-1. The overall profiles are very similar, with prominent C-H stretching peaks of the benzene rings around 3000 cm-1, and one major peak around 1500 cm-1 corresponding to the C-H rocking bending modes of the central benzene ring, followed by lower frequency twisting and bending modes below 1000 cm-1 .
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