H-Bonding controls the emission properties of functionalized carbon nano-dots

Abstract

Bathochromic and hypsochromic shifts in the photo-luminescent spectra of doped and functionalized carbon nano-dots (CDs) arise due to the complex interaction between CDs and the solvent molecules around them. Nitrogen-functionalized carbon nano-dots (N-CDs) were synthesized from citric acid and urea using microwave assisted hydrothermal methods. Optical studies (absorption and photoluminescence) from the as-synthesized N-CDs were carried out in polar protic, aprotic and non-polar solvents. When excited at 355 nm, blue photoluminescence (PL) was observed from the N-CDs dispersed in polar aprotic solvents while green emission was observed in polar protic solvents. In addition to the general solvent effect, the analysis of the luminescence spectra in protic solvents suggests that hydrogen bonding plays a crucial role in regulating the photophysical characteristics of the system. Temperature dependent PL studies and time correlated single photon counting experiments in various solvent dispersions of N-CDs support the role of hydrogen bonding. This indicates that these results depend on the specific interactions observed from the N-CDs and can be thought of as the primary driving force which is then followed by solvent properties like dipole moments. Both the Lippert-Mataga model and Kamlet-Taft parameters were used to support the photophysical properties observed from N-CDs.

Excitons in Carbonic Nanostructures

“…Such effects are similar or even more substantial than that in charge-transfer organic dyes chosen as polarity indicators [189]. Dielectric polarizability and hydrogen bonding with protic solvent molecules [166,190] may contribute to this spectral change [167]. Regarding hydrogen bonding, its effect is local and should involve only small proton accepting/donating surface groups.…”

Carbon Nanodots: A Review—From the Current Understanding of the Fundamental Photophysics to the Full Control of the Optical Response

“…In fact, depending on cases, CDs can be either sensitive to the polarity of the solvent, or to its capacity to form a hydrogen bond, or to both. Because CD surfaces are rich in HB acceptors such as carboxyilic groups, their capability to accept a hydrogen bond from a protic solvent can be absolutely crucial in the stabilization of the excited state, hence in determining the emission peak position [43,208,209]. Solvation studies with the use of steady state and time resolved nanosecond spectroscopy demonstrate these effects through the dependence of the emission band on the polarity of the solvent [43,102,197,210], as well as a solvent-driven modulation of the non-radiative decay rates, hence the quantum yield [43,211].…”

The Impact of Solvents on the Performances of Solution‐Processed Indium Gallium Zinc Oxide Thin‐Film Transistors Using Nitrate Ligands

“…The blue-shifted (hypsochromic) UV-vis spectra can be expected because of the small dipole moment of 2-ME (2.04D) solvent molecules, resulting in negative solvatochomism compared with DIW (2.85D). [33,34] Negative solvatochromism ascribed to ground-state nitrate molecule becomes more stabilized and results in an increased energy gap between the ground state and first excited state. [35,36] However, the various shifts of the absorption with respect to different precursors can only be www.advancedsciencenews.com www.aem-journal.com explained by the reason that nitrate groups in different metal precursors do not completely dissociate.…”