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

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.