Carbon Nanodots: Toward a Comprehensive Understanding of Their Photoluminescence

Abstract

We report the characterization of carbon nanodots (CNDs) synthesized under mild and controlled conditions, that is, in a microwave reactor. The CNDs thus synthesized exhibit homogeneous and narrowly dispersed optical properties. They are thus well suited as a testbed for studies of the photophysics of carbon-based nanoscopic emitters. In addition to steady-state investigations, time-correlated single-photon counting, fluorescence up-conversion, and transient pump probe absorption spectroscopy were used to elucidate the excited-state dynamics. Moreover, quenching the CND-based emission with electron donors or acceptors helped shed light on the nature of individual states. Density functional theory and semiempirical configuration-interaction calculations on model systems helped understand the fundamental structure-property relationships for this novel type of material.

Carbon Nanodots: Supramolecular Electron Donor–Acceptor Hybrids Featuring Perylenediimides

“…[21,[24][25][26][27][28] Thec harge-transfer activity of CNDs has recently been explored, both in ground and excited states, [27,29] for the excited states this was done in conjunction with av ariety of electron donors and acceptors. [26,30] Fori nstance,C NDs have been used together with complementary forms of nanocarbons,s uch as fullerenes,c arbon nanotubes,g raphene,i n tailored charge-transfer systems.Inaleading example,CNDs have been combined with single-walled carbon nanotubes (SWCNTs) affording supramolecular nanohybrids,i nw hich the components function as electron donors and acceptors. [31] Graphene-oxide/CND and methylviologen/CND nanohybrids-brought together by electrostatic interactions-have also been found to feature remarkable charge-transfer activity.…”

“…[27,30] We recently reported an ovel synthetic approach that gives uniform approximately 1nmC NDs. [26] Moreover,w e demonstrated that CNDs form stable charge-transfer hybrids with either electron donors or acceptors.The mutual electron donor-acceptor interactions can be fine-tuned using electrostatic interactions with the negatively charged edge groups of CNDs.F urthermore,t he central units of the CND layers feature extended p-systems,w hich is susceptible for pstacking interactions.…”

Using carbon nanodots as inexpensive and environmentally friendly sensitizers in mesoscopic solar cells

“…A much more pronounced polydispersity is found for the CND1 and CND2 compared to the predominantly UV-absorbing pCND studied previously. 16 Moreover, a slight bimodality is present for CND1 and CND2. ) for several hours.…”

“…[12][13][14][15] We have seen that CNDs are prone to undergo photoinduced charge-transfer in nanohybrid materials, indicating that they are also suitable as photoactive components. [16][17][18] Indeed, several studies have shown that the principle of using such materials as sensitizers in mesoscopic solar cells is sound, although the reported power conversion efficiencies cannot yet compete with inorganic QD solar cells. [19][20][21][22][23][24] We here classify GQDs as structurally well-defined, carbonrich organic molecules that generally require multi-step synthetic procedures in contrast to CNDs, which are usually synthesized in a single step but do not exhibit a well-defined molecular structure.…”

“…It has been proposed that such trap states in the bandgap play an important role for the photoluminescence of CNDs, 16,25,26 and that the trapping effect consists of energy transfer between p-conjugated subdomains within single particles or with the recombination of photogenerated charges at defect centers. 27,28 We found that the fluorescence intensity of CND1 is significantly quenched under acidic conditions (pH 1).…”