Theoretical investigation on the electronic and optical properties of diarylfluorene-based π-stacked molecules as supramolecular semiconductors

The structural substitution effects of different intramolecular π-stacking molecules at 9-position of diarylfluorenes were analyzed. Ground (excited-state) geometric conformations were optimized at B97-D/TZVP (TD-B97D/6-31+G^*) level and their intramolecular π-π interactions were investigated by non-covalent interactions (NCI) theory. UV-vis and photoluminescence (PL) spectra were obtained on the optimized structures at TD-B97D/TZVP level. The results show that the strong π-π interactions mainly focus on the middle area of substituent groups, whereas the outer is the weak π-π interactions. The π-π stacking interactions have different effect on the HOMOs and LUMOs in the diarylfluorenes and diaryldiazafluorenes, resulting in the distinct optical properties.