Synthesizing Red Fluorescent Carbon Dots from Rigid Polycyclic Conjugated Molecules: Dual‐Mode Sensing and Bioimaging in Biochemical Applications

Abstract

Due to enormously attractive merits, such as outstanding chemical stability, excellent biocompatibility, unique photoluminescence characteristics, and salient sensing performances, carbon dots (CDs) present significant potentials in biochemical analysis. [9][10][11][12][13][14][15][16] In biochemical analysis, red fluorescence carbon dots (R-CDs, also red-emission carbon dots) hold better suitability owing to their desirable properties such as low scattering, [17][18][19][20] deep penetration, [21][22][23][24] and low phototoxicity to biological tissues. [25][26][27][28][29][30][31][32][33][34][35][36] Therefore, the development of R-CDs has been extensively explored in previous studies, such as those conducted by Yang and co-workers, [37] Xiong and co-workers, [34] and Yang et al. [35] R-CDs are generally obtained via two strategies: expansion of the π-conjugated (sp 2 hybridization) domain and incorporation of the n-orbital or impurity band between the π and π* orbitals. [38] The former usually uses conjugated molecules, such as benzenediol and its derivatives, [39] dihydroxynaphthalene, [40] and phloroglucinol, [41] as precursors; while the latter prefers to nonconjugated precursors with non-carbon heteroatoms, especially molecules including N, S, P moieties. [42] However, the both do not work with ideal effect. Conjugated molecules are rigid and limit their fusing, resulting in insufficient expansion of the π-conjugated domain; while heteroatoms hinder sp 2 graphite lattice formation. Consequently, new route to realize red emissive CDs still be explored. Among new efforts, an integrated solution based on the above two strategies, especially self-doped, is promising. Consequently, conjugated molecules with heteroatoms (N, S, P, and so on) are selected to synthesize R-CDs. Some molecules with small aromatic ring have been utilized to obtain R-CDs: such as phenylenediamine [43] and derivatives, [44] and other aromatic molecules with, NH 2 , NO 2 , COOH, NCO, or mixed functional groups. [26,45] A concise summary is available from the corresponding discussions in review article. [46] However, rigid polycyclic conjugated molecules (RPCMs) with multiple aromatic rings and substituted functional groups comprise large sp 2 domains, they are rarely utilized to prepare R-CDs, [47][48][49][50] due to the difficulties in fusion that originate from the steric hindrance. Although RPCM-based R-CDs have been demonstrated by Yuan et al., [51] Liu et al., [47] Li et al., [48] Jia et al., [49] Zheng et al., [50] and Tan et al., [45] suitability Red fluorescent carbon dots (R-CDs) are special desirable for biochemical analysis due to good biological compatibility and deep penetration; however, they remain as bottlenecks due to difficulties in expanding the sp 2 domain, especially those are fused from rigid polycyclic conjugated molecules (RPCMs) with heteroatom substituents due to huge steric hindrance and heteroatom blockage toward graphic lattice. Here, an RPCM with heteroatom substituents, 1,5-diamino-4,8-dihydroxyanthraq...

Dual-emission carbon dots for sensitive fluorescence detection of metal ions and ethanol in water

“…The XRD result shows wide diffraction peaks corresponding to the (002) and (100) crystal planes of the graphite structure at 23 and 42 respectively. 51 The Raman spectrum further proves that the asprepared red CDs have a graphite-like structure (Fig. S1 †).…”

“…41 In contrast, the optimal excitation spectrum has double peaks in the range of 500 nm to 600 nm, which is in good agreement with the results of the absorption spectrum, indicating that the mixed sp 2 domain may lead to the red emission of the carbon core. 51 Moreover, the emission spectrum has the strongest emission peak at 598 nm, and there is also a shoulder peak near 650 nm. Subsequently, the time-resolved PL decay curve of CDs was obtained under the optimal excitation (Fig.…”

“…3c, PL spectra were investigated under different excitations to further explore the PL characteristics of the red CDs, indicating that CDs have emission characteristics unrelated to excitation, which also confirms again that the red fluorescence of the CDs might be caused by the sp 2 domain of the carbon core. 51 Furthermore, the PL spectra of the red CDs at different concentrations were also studied. The results in Fig.…”

Red emissive carbon dots: a promising next-generation material with intracellular applicability

“…36,63 The RCDs offer great promise in contributing to reporting 3D structures of specimens, and bioimaging of subcellular structures and various tissues in a multicellular physical entity. [64][65][66][67][68] The properties like red emission and two photon fluorescence (TPF) play an important role in achieving excellent targeting capabilities. The nitrogen-containing structures, such as pyrrolic N along with CQN and CQO functional groups, influence the intensive red fluorescence along with the emission efficiency.…”

Deep‐Red to Near‐Infrared Carbon Dots in Biosensing and Bio‐medical Applications

“…The narrowing of the band gap due to the expansion of the sp 2 carbon crystal cluster also directs the emission redshift of CDs. [ 43 ] The R‐CDs synthesized by a one‐step solvothermal method with 1,5‐diamino‐4,8‐dihydroxy‐anthraquinone (DAQ) as the source of C and N consist of a large conjugated structure with many C=C linkages and a certain number of C=N linkages, which can form a mixed sp 2 structural domain that contributes to red luminescence.…”