Activating Electronic Delocalization: Through-Space Lone-Pair Interactions versus Hydrogen Bonding

It
is still unclear how weak interactions specifically affect electronic
structures. Here, we systematically reduce the number of N–H
bonds within diarylmethane (DAM), precisely diminishing the number
of hydrogen bonds (H-bonds). Contrary to the widely reported result
that H-bonds could enhance molecular brightness by promoting electron
delocalization, DAMs lacking H-bonds exhibit superior luminescence,
compared to DAMs with H-bonds in both dilute solutions and solid states.
It is indicated that H-bonds tend to induce n-electron
localization, preventing the formation of through-space lone-pair
conjugation (n–n TSC). In
addition, unlike the widely studied through-space π–π
conjugation that only existed in the aggregate state, the n–n TSC can even stabilize the conformation
and is expressed in dilute solutions. Herein, we not only achieve
bright white-light emissions in nonconjugated small molecules but
also reveal the surprisingly competitive relationship between H-bonds
and n–n TSC in electronic
delocalization, providing a new strategy for designing excellent optoelectronic
materials via the n-electron bridge.