Solvent Effects: A Signature of J- and H- Aggregate of Carbon Nanodots in Polar Solvents

The secret behind excitation dependent/independent photoluminescence of carbon nanodots (CDs) is not yet revealed completely. To address this issue, a detailed investigation on solvent polarity dependent optical properties of citric acid-urea co-derived nitrogen doped carbon nanodots (NCDs) was carried out. The interpretation on UV-visible spectral data reveals presence of H-aggregates formed through hydrogen bonding. In addition, dipole-dipole interaction mediated J-aggregates is clearly evident. The broad and intense excitation band of NCDs is mostly contributed by highly emissive J-like self-assembly of H- aggregates in polar solvents. Time resolved fluorescence spectra of NCDs show tri-exponential decay kinetics. The three lifetime components corresponds to long lived H-aggregates, short lived J-aggregates and JH-aggregates of intermediate lifetime. Moreover, fluorescence of NCD is influenced by concentration and storage time. Accordingly, mismatch in spectral shapes of excitation and absorption spect...