A rational design of carbon dots via the combination of nitrogen and oxygen functional groups towards the first NIR window absorption†
‡a
Fitri Aulia
Permatasari,
‡a
Diva Addini Maghribi
Muyassiroh,
a
Arum Sinda
Santika,
a
Citra Deliana Dewi
Sundari,
bc
Atthar Luqman
Ivansyah,
de
Takashi
Ogi
f
and
Ferry
Iskandar
*ag
Abstract
Carbon dots (CDs) that exhibited a first near infrared (NIR) window absorption were designed by a combination of nitrogen and oxygen surface functional groups. Time-dependent density functional theory (TD-DFT) calculations were initially used to investigate the appropriate combination of N and O surface functional groups to effectively generate a first NIR window absorption. Guided by the TD-DFT predictions, the CDs that exhibit a first NIR window absorption were successfully synthesized by a microwave-assisted hydrothermal method. Comprehensive study based on TD-DFT calculations and experiments suggested that the carbonyl group (C![[double bond, length as m-dash]](https://www.rsc.org/images/entities/char_e001.gif)
O) is the most efficient way to down-shift the unoccupied molecular orbital energy, reducing the energy gaps of the CDs, while the nitrogen configurations in the N-pyrrolic configuration could provide an excited electron via free electron-donation to the π system of the main structure of the CDs. Thus, the N-pyrrolic CDs—CO is the preferable structure to generate the absorption in the first NIR window region. This study provides deep insights into an efficient and effective strategy for tailoring CD absorption through surface modification.
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