Fig. 7. (a) Absorption of the red emissive CNDs synthesized using different precursor molecules. (Blue color) CNDs synthesized using OPDA as the only precursor molecule, (green color) CNDs synthesized from OPDA and dopamine (DOP) and (red color) CNDs synthesized from OPDA and catechol (CAT). (b–d) Emission spectra for the CNDs synthesized from OPDA, OPDA–DOP and OPDA–CAT. It is seen that the emission intensity or the extent of the blue component depends on the precursor molecules. (e & i) Absorption spectra of column separated red, green and blue components for OPDA–DOP and OPDA–CAT. The observed spectral features have similarities up to a large extent. (f–h) The emission spectra with the change in excitation wavelength for the red, green and blue components for OPDA–DOP and for (j–l) OPDA–CAT. Interestingly, the red emission spectral features in all the three cases bear extreme similarities, suggesting the origin from a similar type of chemical structure. The excitation independent part in the blue and green component also bears similarities, while the excitation dependent part has a slight difference, suggesting the slight difference in the extent of core structure formation.