Formation of Ultra-Narrowband SWIR J-Aggregate Materials and Their Applications in Multispectral Optoacoustic...

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.