Single Meta-Phenylenediamine Carbon Dot Solvatochromic Spectral Imaging

Carbon dots (CDs) synthesized from meta-phenylenediamine (mPD) exhibit intriguing photophysical properties, yet the structural origins of this behavior remain challenging to reveal. Here, we employ continuously controlled spectral-resolution (CoCoS) microscopy alongside rigorous theoretical modeling to examine single-dot spectral heterogeneity and solvatochromism of mPD-derived CDs. Experimental findings show notable fluorescent emission peak shifts from ∼496 to 510 nm and moderate excited-state dipole moment changes by ∼1.9 D, in response to solvent polarity. Density functional theory calculations validate this hypothesis. They indicate that structured solvent-induced stabilization is especially pronounced in water. This process forms protective hydration shells that enhance emission lifetimes. Integrating these insights into prior knowledge from mPD conjugation and SU-8 epoxy precursor studies, we conclusively identify the CDs as planar, quasi-two-dimensional aromatic emitters, thus, significantly advancing our fundamental understanding for mass production and showing their potential applications as optoelectronic nanoscale sensors and biomarkers.