Fluorescence quenching mechanism of 9-hydroxyphenal-1-one carbon quantum dots by Cu2+ ions: An experimental and computational investigation

Abstract

A combination of experimental and computational methods was used to study the Cu2+ ions recognition by 9-hydroxyphenal-1-one carbon quantum dots (HPHN-CQDs). HPHN-CQDs were proved to be an efficient fluorescent probe that can detect Cu2+ ions with high selectivity and sensitivity, and the detection limit was 4.8 nM. We performed a detailed analysis of the fluorescence quenching mechanism of HPHN-CQDs by means of density functional theory (DFT) and time-dependent density functional theory (TDDFT). The orbital interaction diagram indicated that the presence of Cu2+ can affect the luminescence behavior of HPHN by changing its orbital distribution. In addition, the electron was transferred from the excited HPHN to the 3d orbital of Cu2+, which would hinder the recombination of electron-hole pairs and promote the fluorescence quenching of HPHN-CQDs. The photophysical process revealed that the fluorescence rate constant of HPHN-Cu2+ was substantially decreased compared with that of HPHN, which is consistent with the experimental results.