Solvatochromic Carbon Dots

Exploring the solvatochromic processes of carbon dots (C-dots) is significant for both fundamental science and their corresponding applications. At present, there are a few relevant concerns, such as the exact solvatochromic photophysical picture and positive and negative solvatochromism versus the composition and structure of C-dots, which have remained open questions. Herein, by our group's adequate separation/purification technique based on systematic investigation, four kinds of highly purified C-dots are isolated and obtained. Through quantitative analysis and comparison, we find that the solvatochromic behaviors of C-dots result from their intrinsic charge distribution. Only if the C-dots have a donor-π-acceptor configuration can they exhibit distinct solvatochromism through "intramolecular" charge transfer effects; furthermore, the direction and magnitude of the absorption/fluorescence band shift of the C-dots in different (high- and low-polarity and aprotic and protic) media are dependent on the ratios of the acceptors to donors. In contrast, for the C-dots with the donor-π or acceptor-π configuration, negligible solvatochromic behaviors are observed due to insufficient charge transfer within the corresponding particles.