Optical processes in carbon nanocolloids

Light is the original source of most energy on Earth, allowing us to see and live. It also central many technological processes. Therefore, innovative nanomaterials that can absorb, generate, or further exploit light are utmost importance, having potential become pervasive in our lives. This case for carbon nanocolloids, which ubiquitous, biocompatible, inexpensive, three important prerequisites their broader application different fields technology. Yet, despite intense research a number years, unifying picture describing excited-state properties these nanocolloids lacking. possibly time when this approach should be reversed, embracing inherent diversity excited states carbon-based particles, enable focus engineering optical based structural variability. A deeper understanding molecular features emerging as one key factors, will allow unlocking processes appearing out reach, unfolding full potent family nanomaterials. In recent dots, graphene quantum other have attracted mounting interest readily available, non-toxic, tailorable One fascinating luminescence, origin remains dispute. The lack hampers use technological, environmental, biomedical Here, we review current knowledge related properties, inviting researchers embrace complexity nanocolloids. We point fundamental problems associated with structure, photophysics, photochemistry highlight multiple directions future exciting class Carbon (CNCs) cumulative term here refer plethora dispersable nanoscale particles made predominantly from atoms. They encompass nanostructures known nanoonions, black, typical dimensions below around 10 nanometers.1Baker S.N. Baker G.A. Luminescent nanodots: emergent nanolights.Angew Chem Int Ed Engl. 2010; 49: 6726-6744Crossref PubMed Scopus (3551) Google Scholar, 2Lim S.Y.Y. Shen W. Gao Z. dots applications.Chem. Soc. Rev. 2015; 44: 362-381Crossref 3Sun Y.-P. Dots. Springer Nature, 2020Crossref (12) Scholar share lot among scientists, such strong low toxicity, water-solubility, ease synthesis, high surface area, possibility tune properties.3Sun fluorescence CNCs likely attractive feature, marking difference common nanomaterials, nanotubes microscale platelets oxide. Specifically, display an excitation-dependent emission accompanied by large Stokes shifts uncommon organic dyes. These stimulated broad been subject investigation, however, still lacking.4Xiong Y. Schneider J. Ushakova E.V. Rogach A.L. Influence fluorophores field chemically synthesized dots.Nano Today. 2018; 23: 124-139Crossref (108) 5Sciortino A. Cannizzo Messina F. review—from photophysics control response.C. 4: 67Google 6Demchenko Excitons carbonic nanostructures.C. 2019; 5: 71Google Besides fluorescence, give rise several phosphorescence chiroptical activity being prominent. Management charge photons state scientifically technologically intriguing. Fundamental studies at single-particle level exploitation less spectroscopic techniques contribute CNCs. provide tutorial CNCs, including aspects frequently discussed, phosphorescence. Representative examples photon- charge-management highlighted, vision opportunities arising versatility CNC shared readers. include variety sub-categories patterns atomic connectivity anisotropy. Although boundaries between categories blurred, few main identified, recurrent literature present rather distinctive traits (Figure 1).7Xia C. Zhu S. Feng T. Yang M. B. Evolution synthesis dots: carbonized polymer dots.Adv Sci (Weinh). 6: 1901316Crossref (280) At end spectrum amorphous polymeric structures minimum degree carbonization, identified (CPDs). Structures increased carbonization referred nanodots (CNDs), whereas multilayer stacks graphitic sheets typically (CQDs). Finally, nanometer-sized fragments crystalline up layers stacked (GQDs), completing range possibilities. requires harsh conditions, needed formation new carbon-carbon bonds. Common precursors small molecules undergoing decomposition, polymerization, under hydrolytic, solvothermal, pyrolytic conditions. Microwave irradiation precursor solutions has proven effective tool, providing much shorter reaction times.8de Medeiros T.V.V. Manioudakis Noun Macairan J.-R. Victoria Naccache R. Microwave-assisted applications.J. Mater. Chem. 7: 7175-7195Crossref cases, proceeds through followed incomplete temperature prolonged times. scenario observed so-called top-down larger ultrasonication, laser ablation, arc discharge, electrochemical etching, effectively cutting into smaller pieces.2Lim over final methods lower compared achieved using bottom-up methods. all detailed structure materials vary significantly, even within same category sample. general consequence that—in principle—the may arise portion whole sample particularly active. intrinsic indeed reason why better material, than precise entities. Using analogy taken might consider variability resembling enzyme families rich structures. Such feature caution drawing conclusions study single just materials. For reason, performing careful extensive material purification characterization critical support specific claims offers scientific community solid basis rationalize behaviors. When used precursors, dialysis ideal method, could coupled filtration steps, eliminate carbonaceous side products. As recently discussed detail elsewhere, membranes appropriate weight cutoff employed.9Essner J.B.B. Kist J.A.A. Polo-Parada L. G.A.A. Artifacts errors ubiquitous presence fluorescent impurities nanodots.Chem. 30: 1878-1887Crossref (121) Concerning characterization, evaluation size transmission electron microscopy (TEM) and/or force required, although it often not sufficient prove Indeed, require solvent evaporation, concomitant concentration sample, was aggregates detected analyzing molecules.10Khan Sharma Ghoshal Jain Hazra M.K. Nandi C.K. Small nanocrystals resemble terms properties.Chem. Sci. 9: 175-180Crossref displayed d spacing comparable graphite interlayer distance about 0.33 nm. Dynamic scattering overcome limitation, sizes make analytical technique challenging. To understand nature formed X-ray photoelectron spectroscopy (XPS) employed results very helpful uncover elemental composition type bonds Considering penetration depth XPS analysis (a nanometers) reveal contributions segments percentage sp2- sp3-carbon With aim, complementary thermogravimetric (TGA). graphitized tend decompose higher temperatures and, therefore, TGA profile provides good indication study. Additional information functional groups obtained infrared (IR) nuclear magnetic resonance (NMR) spectroscopies. particular, 1H 13C-NMR data useful verify absence starting byproducts purified material. Further entities offered two-dimensional NMR spectroscopy, modeling, insights homogeneity sample.11Qu Z.B. W.J. Wang Romanenko Kotov N.A. Diverse nanoassemblies mineralogical counterparts.Angew. Int. Ed. 2020; 59: 8542-8551Crossref (16) Chemists, physicists, mineralogists, geoscientists too interested expertise, combined reflected terminology discuss properties. aid readers coming backgrounds, briefly overview types commonly encountered. start with, molecular-like, meaning localized onto fragment optically active features, occurring fluorophores. Many states. some promotion higher-energy orbital creates separation, described exciton, hole electrostatic forces. description semiconductor (QDs) describe albeit inaccurate incomplete. exciton delocalized dominates transition, producing confinement effect. gives approximation phenomena, unable correctly example, dependence wavelength excitation cannot explained framework. complex materials, trap only influence behavior but goal property engineering. trapped defects lattice molecular-like interfere responsible transition. Again, borrowed semiconductors, be, fact, applicable because contribution component substantially one. see, tightly representation “core” “shell.” “shell” refers regions sensitive external environment. GQDs CQDs, reflect defined spatial separation distinct regions, correspondence mostly systems like CNDs CPDs. core-shell cases QDs CdSe/ZnS QDs, where core shell clearly phase boundary. peculiarity must remembered considering shell. simplest method generate absorption photon. exhibit ultraviolet (UV) region long tail extending visible near-infrared (NIR) regions.1Baker Scholar,3Sun characteristics influenced ? domains, shape, composition, 2). short bands 300 nm correspond ? ?? transition sp2 aromatic carbons, while 400 due n C=O groups.12Sudolská Dubecký Sarkar Reckmeier C.J. Zbo?il Otyepka Nature oxygen-functionalized dots.J. Phys. 119: 13369-13373Crossref (65) transfers transfer transitions spectral region.12Sudolská above attributed extended domains states, passivation modification process. modifications affect red-shifted result hydroxyl, carboxyl, epoxy, narrow levels.12Sudolská Moreover, red-shift attained introducing nitrogen lattice.13Holá K. Sudolská Kalytchuk Nachtigallová D. Graphitic triggers red dots.ACS Nano. 2017; 11: 12402-12410Crossref (322) Most coefficients yields (QYs) NIR region. developing strategies improve QY open challenge. desirable respect multi-photon processes, leading wavelength. promising numerous applications, biological imaging enhanced tissue reduced auto-fluorescence background excitation.14Cao X. Meziani M.J. Lu H. Luo P.G. Lin Harruff B.A. Veca L.M. Murray et al.Carbon multiphoton bioimaging.J. Am. 2007; 129: 11318-11319Crossref (1756) Surface lead two-photon instance, interactions sulfoxide carbonyl outer edges produced emission. 1,400 nm, oxidized emit two-photon-induced three-photon-induced emission.15Li Jing P. Sun An Shan Zhou Han Zhai al.Near-infrared excitation/emission multiphoton-induced dots.Adv. 30e1705913Crossref (254) Polymers passivating functionalization agents enhance optoelectronic derivatives polythiophene inducing sulfur doping via hydrothermal route, exhibited efficient excitation, though, 0.2%.16Lan Zhao Zhang Yan Guo Niu G. al.Two-photon-excited emissive multifunctional photothermal therapy.Nano Res. 10: 3113-3123Crossref (145) From examples, clear suitable environment facilitate absorption, nitrogen-doped CQDs (N-CQDs) appear platform achieve absorption. dopamine o-phenylenediamine were prepare facile, high-output NIR-emissive N-CQDs displaying comes 710 26.28%.17Lu Sui Liu Chen Jin Near-infrared photoluminescent polymer-carbon fluorescence.Adv. 29: 1603443Crossref (481) emerges heteroatom role promoting charge-transfer preferentially N-CQDs. Extending strategy, co-doping N F atoms promoted donor-acceptor interactions, four-photon absorption.18Jiang Ding Xu Hu Li Q. Tian Bi UV–vis–NIR full-range responsive cross sections deep-red nucleoli vivo.Small. 16e2000680Crossref (74) kind chiral nanoparticles, represent nanomaterials.19Guerrero-Martínez Alonso-Gómez J.L. Auguié Cid M.M. Liz-Marzán individual collective chirality metal nanoparticles.Nano 2011; 381-400Crossref (238) Scholar,20Ru Ai Jia Tang Recent advances applications.Nano 34: 100953Crossref (23) Scholar21Ðor?evi? Arcudi D’Urso Cacioppo Micali N. Bürgi Purrello Prato Design principles help convey level.Nat. Commun. 3442Crossref (85) Scholar22Suzuki Elvati Qu Z.-B. Kim Jiang Baumeister E. Lee Yeom Bahng J.H. al.Chiral 2016; 1744-1755Crossref (193) Both three-dimensional geometry light-matter interaction left right circularly polarized light. manifestations circular dichroism (CD), implies left-handed right-handed CD spectra information, e.g., identity stereoisomers. Chiroptical essential life sciences, medicine, chemistry, telecommunications.23Ma De Moura A.F. Wu Kuang Chiral inorganic nanostructures.Chem. 117: 8041-8093Crossref (395) first strategy obtain attachment moieties 3A).24Peng Gupta B.K. Romero-Aburto Ge Song Alemany L.B. Zhan al.Graphene derived fibers.Nano Lett. 2012; 12: 844-849Crossref (1769) Scholar,22Suzuki GQD L- D- cysteines afforded L-GQDs D-GQDs, mirror-symmetrical peak 210–220 corresponding amino acid groups, broadened hybridization edge sheets.22Suzuki Furthermore, resulting acquire twisted mirror asymmetrical 250–265 sheet, representing (particle-wide) excitonic simple esterification enantiomerically pure (R)- (S)-2-phenyl-1-propanol. able supramolecular assemblies pyrene.25Vázquez-Nakagawa Rodríguez-Pérez Herranz M.A. Martín Chirality dots.Chem. Commun.(Camb). 52: 665-668Crossref ligands, (?)-sparteine (+)-sparteine.26Vulugundam Misra S.K. Ostadhossein Schwartz-Duval A.S. Daza E.A. Pan (-)/(+)-Sparteine induced chirally-active nanoparticles enantioselective racemic mixtures.Chem. 7513-7516Crossref Being suspended water, showed peaks 195–220 route introduce during nanomaterial. early prepared treatment citric simultaneously capping D-cysteine system.27Zhang Huang Kang One-step recognition.RSC Adv. 59956-59960Crossref Later on, D-methionine, D-glucose, D-glucosamine, L-methionine (L-Met), L-aspartic acid, L-alanine. aspect racemization occurs conditions necessary system tolerance (R,R)- (S,S)-1,2-cyclohexanediamine combination arginine, reacting microwave-assisted performed 240°C afford 3B).21Ðor?evi? Scholar,28Ðor?evi? Preparation, engineered nanodots.Nat. Protoc. 14: 2931-2953Crossref (42) (S,S)-CNCs aqueous solution presents two negative positive Cotton effects 260 320 porphyrin assemblies, showing possible embedded composite applications.21Ðor?evi? self-assembly nanocomposites/supraparticles advance applications catalysis, biology, nanotechnology. regard, vortices utilized induce oxide (GO) aggregates.29Di Mauro Randazzo Spanò S.F. Compagnini Gaeta Paolesse Pomarico Di Natale Villari V. al.Vortexes its non-covalent hosts.Chem. 13094-13096Crossref turn asymmetry non-covalently bound derivatives, measurable signals. Stirred dispersions GO deposited quartz capture transient, vortex-induced unusual unavailable means. Similarly, composites nanocarbons macro-tonano twisting deformation serve photonics UV, vis, parts spectrum.30Kim Arteaga O. Jo Yoo S.J. S.G. J.G. Reconfigurable nanocomposites macro- nanoscale.Nat. 15: 461-468Crossref (163) facile scalable developed synthesize N-doped cellulose nanocrystals.31Chekini Prince Mundoor Smalyukh I.I. Kumacheva nanocrystals.Adv. Opt. 8: 1901911Crossref (17) geometrical arrangement preserve glucose, confirmed spectra, allows fluorescence-detected CD, i.e., observation stronger upon handedness, other, confused emission, covering wide moderate QYs. Several photoluminescence (PL) modes highlighted: delayed phosphorescence, aforementioned up-conversion PL.4Xiong funda