Formation of Ultra‐Narrowband SWIR J‐Aggregate Materials and Their Applications in Multispectral Optoacoustic Tomography Imaging

ABSTRACT Ultra‐narrowband materials provide exceptional spectral purity for high‐resolution imaging, precision sensing, and advanced photonic applications, yet molecular systems achieving ultra‐narrowband absorption in the short‐wave infrared (SWIR) remain exceedingly rare. This scarcity arises from the intrinsic trade‐off between long‐wavelength absorption, vibrational broadening, and the structural disorder that typically emerges during disordered aggregation. Here, we introduce SWIR cyanine dyes rationally engineered through controlled steric hindrance, sulfonate‐mediated electrostatic interactions, and π‐conjugation design to promote highly ordered J‐aggregation. The optimized dye, IRJ1089, assembles into remarkably stable and encapsulation‐free J‐aggregates, exhibiting high optoacoustic signal generation efficiency and ultra‐narrowband absorption at 1089 nm with a FWHM of 164 cm −1 (19.4 nm). Based on a structural analogue's (IRJ1021) crystallographic data and computational analyses, we propose that electrostatic interlocking between sulfonate groups and the polarized π‐backbone, together with favorable slip‐stacking geometry, promotes aggregate order and enhances the J‐aggregates’ stability. IRJ1089 J‐aggregates support high‐contrast multispectral optoacoustic tomography (MSOT) imaging in vasculature deep inside rats (∼1.2 cm), enable real‐time monitoring of antihypertensive drug‐induced aortic dilation, and allow crosstalk‐free SWIR multiplexed imaging for diagnosing colorectal cancer‐associated intestinal obstruction. These findings establish a generalizable blueprint for designing ultra‐narrowband J‐aggregating dyes and provide valuable insights into other SWIR photonic materials in multiple areas.