Carbon nanodots (CNDs) synthesized from citric acid and formyl derivatives, that is, formamide, urea, or N‐methylformamide, stand out through their broad‐range visible‐light absorbance and extraordinary photostability. Despite their potential, their use has thus far been limited to imaging research. This work has now investigated the link between CNDs’ photochemical properties and their chemical structure. Electron‐rich, yellow carbon nanodots (yCNDs) are obtained with in situ addition of NaOH during the synthesis, whereas otherwise electron‐poor, red carbon nanodots (rCNDs) are obtained. These properties originate from the reduced and oxidized dimer of citrazinic acid within the matrix of yCNDs and rCNDs, respectively. Remarkably, yCNDs deposited on TiO2 give a 30% higher photocurrent density of 0.7 mA cm−2 at +0.3 V versus Ag/AgCl under Xe‐lamp irradiation (450 nm long‐pass filter, 100 mW cm−2) than rCNDs. The difference in overall photoelectric performance is due to fundamentally different charge‐transfer mechanisms. These depend on either the electron‐accepting or the electron‐donating nature of the CNDs, as is evident from photoelectrochemical tests with TiO2 and NiO and time‐resolved spectroscopic measurements. Electron‐rich, yellow carbon nanodots (yCNDs) are obtained by the in situ addition of NaOH during synthesis, while otherwise electron‐poor, red CNDs (rCNDs) are formed. The physicochemical properties, including photoelectric performance, depend on the chemical structure, that is, either the reduced (electron donating) or oxidized (electron accepting) dimer of citrazinic acid in the polymeric citric acid matrix of yCNDs or rCNDs, respectively.