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.