Anisotropic Near‐Infrared Amplified Spontaneous Emission in Single‐Benzene Organic Crystals

ABSTRACT

Organic materials capable of near‐infrared (NIR) amplified spontaneous emission (ASE) are attractive for compact photonic and sensing technologies, yet efficient NIR ASE typically requires extended π‐conjugated frameworks. Herein, we report a structurally simple donor– π –acceptor (D– π –A) dye molecule, butyl (2E,4E)‐2‐cyano‐5‐(4‐(dimethylamino)phenyl)penta‐2,4‐dienoate ( M1 ), containing only a single benzene ring, that exhibits efficient NIR emission and ASE. Despite its limited π ‐conjugation, M1 crystals show a photoluminescence quantum yield (PLQY) of up to 19% and NIR emission centered at 760 nm with a large Stokes shift. Notably, M1 crystals over a broad range of dimensions exhibit ASE, indicating that ASE generation does not require a narrowly defined crystal size. The ASE response also varies substantially with crystallographic orientation. Block‐ and plate‐like crystals exhibit direction‐dependent ASE along distinct crystallographic axes, whereas rod‐ and needle‐like crystals simultaneously generate two ASE bands centered at approximately 750 and 670 nm along the growth direction. In contrast, the analogous tert‐butyl derivative exhibits markedly weaker emission and no detectable ASE, underscoring the importance of substituent flexibility and crystal packing. These results show that pronounced and direction‐dependent NIR ASE can be realized in organic crystals with remarkably limited π ‐conjugation.