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Mechanism of Charge Separation and Frontier Orbital Structure in Graphitic Carbon Nitride and Graphene Quantum Dots
Author(s) -
Ullah Naeem,
Chen Shunwei,
Zhang Ruiqin
Publication year - 2018
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201800451
Subject(s) - quantum dot , excited state , graphene , graphitic carbon nitride , materials science , density functional theory , electronic structure , chemical physics , atomic orbital , nanotechnology , chemistry , photocatalysis , atomic physics , electron , physics , computational chemistry , biochemistry , quantum mechanics , catalysis
Graphene quantum dots (GQDs) and carbon nitride quantum dots (CNQDs), the latest addition to the carbon material family, are promising materials for numerous novel applications in optical sensing, photocatalysis, biosensing, and photovoltaics. However, understanding the photocatalytic capability of CNQDs compared to GQDs requires investigations of the charge behavior on the excited state energy surface. In this work, through time‐dependent density functional tight binding (TD‐DFTB) calculations, we show that CNQDs exhibit superior ground state frontier orbitals (FOs) localization. Strong localization of the FOs and excited state charge separation observed in the first excited state are caused by the relaxation of the structure. Excited energy surface investigations reveal spatial confinement of FOs to the stretched C−N bonds due to excited state structural relaxation. On the other hand, no such localized FOs structure was found for GQDs, presumably caused by its strong π‐conjugated configuration not allowing large structural changes upon excitation. The optical absorption and emission of CNQDs is sensitive to size and does not show large variations with the shape of the QD. Our approach provides an explanation for the origin of the enhanced photocatalytic performance of CNQDs over GQDs and their characteristic FOs localization.