π-Bridge-Driven Design of Donor-π-Acceptor Organic Crystals for Stable, Long-Wavelength Near-Infrared Nanolasers

The development of near-infrared (NIR) organic lasers has long been constrained by inefficient excited-state intramolecular proton transfer (ESIPT) and limited electronic delocalization, which restrict both performance and scalability. In this study, we demonstrate that subtle molecular modifications can improve laser properties. By introducing a π-bridge-enhanced donor-π-acceptor (D-π-A) architecture in the molecule MDS-DHAQ, we improve molecular planarity and extend π-conjugation. This strategic adjustment is associated with predominantly K*-type emission, consistent with an ESIPT-based four-level lasing scheme. Through self-assembly, MDS-DHAQ molecules spontaneously form well-ordered micro/nanocrystals that serve as the gain medium and resonant cavity for lasing. These self-assembled crystals exhibit single-mode lasing at 940 nm, with a low threshold of 3.8 μJ cm−2 and a linewidth of approximately 0.37 nm. Furthermore, they show a 10% reduction in lasing intensity after 10,000 pump pulses. This work highlights how molecular alterations can tune the physical properties of materials, offering an approach that integrates molecular engineering and self-assembly. The resulting NIR organic lasers have potential applications in integrated photonics and optoelectronics.