Influences of Intramolecular Weak Interactions on Conjugation

Organic π-conjugated compounds have received great research attention due to their wide optoelectronic applications. Previous studies on tuning single molecular photoelectric properties of organic π-conjugated compounds focused on developing new π- skeletons and introducing electron-donating and withdrawing substituents. However, the influences of intramolecular weak interaction on the optoelectrical properties of organic π-conjugated compounds are lacking of study. Herein, we designed and synthesized compounds 1～6 and 7～12 via Buchwald-Hartwig/Suzuki coupling reactions, with 2,2paracyclophane (cyclophane), triptycene, and 9,9’-spirobifluorene (spirofluorene) as the linking units, two electron-rich diphenylamino or electron-deficient naphthalimide as the substituents. In compounds 1～6 and 7～12, the two electron-rich or electron-deficient centers interact with each other via homo-conjugation, cross-conjugation, π-π stacking, and π-direct conjugation. Photophysical and electrochemical measurements revealed that at neutral state, interactions (conjugation-effect) created by homo-conjugation in spirofluorene were lower than those created by direct π-conjugation, but were stronger than those created by cross-conjugation in spirofluorene, homo-conjugation in triptycene, and π-π stacking in cyclophane. When electron-rich compounds 1～6 lost one electron, converting into a monocation, conjugation effect decreases in the following order: Direct π-conjugation, homo-conjugation in spirofluorene, homo-conjugation in triptycene, cross-conjugation in spirofluorene. All these results demonstrated that optoelectronic properties of π-conjugated organic molecules could be tuned by the intramolecular weak interactions.