# Dual‐State Photophysical Modulation via Bifurcated Hydrogen Bonding in a U‐Shaped Dipyridophenazine‐Cored Donor‐π‐Acceptor‐π‐Donor Fluorophore

## TL;DR

A U-shaped fluorophore with a dipyridophenazine core forms hydrogen bonds that change its light emission properties in both liquid and solid states.

## Contribution

A U-shaped D–π–A–π–D fluorophore enables bifurcated hydrogen bonding for dual-state photophysical modulation.

## Key findings

- Bifurcated hydrogen bonding with sulfonamides or water causes red-shifted emission and enhanced photoluminescence.
- The fluorophore's optical responses persist in solid-state polymer matrices without aggregation.
- Single-crystal X-ray analysis confirms bifurcated hydrogen-bonding complex formation.

## Abstract

Modulating photophysical properties via hydrogen bonding offers a powerful strategy for designing supramolecular functional materials and responsive optical systems. Here, we present a U‐shaped dipyridophenazine (DPyPHZ)‐cored donor–π–acceptor–π–donor (D–π–A–π–D) scaffold that serves as a hydrogen‐bond receptor capable of forming bifurcated hydrogen bonds, enabling simultaneous modulation of both ground and excited states. We developed an efficient synthetic route to this π‐conjugated system, and demonstrated that its absorption and emission spectra undergo pronounced red‐shifts upon 1:1 complexation with neutral hydrogen‐bond donors such as sulfonamides and even water. Spectroscopic analyses reveal that the hydrogen‐bonding interaction stabilizes the charge‐transfer excited state, leading to enhanced photoluminescence quantum yield (PLQY) and color modulation. Notably, these optical responses persist in the solid state when embedded in a polymer matrix, enabling emission color switching without fluorophore aggregation. Single‐crystal X‐ray analysis confirmed the formation of a well‐defined bifurcated hydrogen‐bonding complex in the solid state. Comparative studies with structural analogues highlight the importance of the electron‐density hotspot in DPyPHZ for selective and directional hydrogen bonding. This work introduces a supramolecular design strategy for precise dual‐state photophysical control, providing a platform for environmentally responsive luminescent materials with potential in sensing, imaging, and optoelectronic applications.

A donor–π–acceptor–π–donor (D–π–A–π–D) fluorophore bearing a U‐shaped dipyridophenazine core forms bifurcated hydrogen bonds with neutral donors such as sulfonamides or water. This interaction modulates both ground and excited states, enabling red‐shifted emission and enhanced photoluminescence in solution and solid state.