Molecular transition-metal–ligand complexes are emerging as useful paradigms in materials science. Transition metal complexes have diverse metal d electron configurations, oxidation states, coordination numbers and geometries such that they can undergo a diverse array of electronic transitions. Metal-to-ligand charge-transfer transitions and their associated excited states are especially attractive given their rich redox properties and robustness. This chemistry is accessible by appropriate choice of low-valence metal centres and strong π-acceptor ligands. An in-depth fundamental understanding of their charge-transfer, assembly and structure–property relationships is important to allow us to rationally design complexes and tune their characteristics for an intended application. In addition to their attractive light-harvesting and photocatalytic applications, this Perspective describes recent developments in the use of transition metal complexes as materials in phosphorescent organic light-emitting diodes and resistive memory devices.
This is a preview of subscription content, access via your institution
Access Nature and 54 other Nature Portfolio journals
Get Nature+, our best-value online-access subscription
$29.99 / 30 days
cancel any time
Subscribe to this journal
Receive 12 digital issues and online access to articles
$119.00 per year
only $9.92 per issue
Rent or buy this article
Prices vary by article type
Prices may be subject to local taxes which are calculated during checkout
Similar content being viewed by others
Solomon, E. I. & Lever, A. B. P. Inorganic Electronic Structure and Spectroscopy, Applications and Case Studies Vol. 2 (Wiley-Interscience, 1999).
Turro, N. J., Ramamurthy, V., Ramamurthy, V. & Scaiano, J. C. Principles of Molecular photochemistry: An Introduction (University Science Books, 2009).
Nocera, D. G. Chemistry of the multielectron excited state. Acc. Chem. Res. 28, 209–217 (1995).
Esswein, A. J. & Nocera, D. G. Hydrogen production by molecular photocatalysis. Chem. Rev. 107, 4022–4047 (2007).
Lee, J. et al. Hot excited state management for long-lived blue phosphorescent organic light-emitting diodes. Nat. Commun. 8, 15566 (2017).
Mason, W. R. & Gray, H. B. Electronic structures of square-planar complexes. J. Am. Chem. Soc. 90, 5721–5729 (1968).
Adamson, A. W. & Demas, J. N. New photosensitizer. Tris(2,2ʹ-bipyridine)ruthenium(ii) chloride. J. Am. Chem. Soc. 93, 1800–1801 (1971).
Jennette, K. W., Lippard, S. J., Vassiliades, G. A. & Bauer, W. R. Metallointercalation reagents 2-hydroxyethanethiolato (2,2ʹ,2ʹʹ-terpyridine)-platinum(ii) monocation binds strongly to DNA by intercalation. Proc. Natl Acad. Sci. USA 71, 3839–3843 (1974).
Mann, K. R., Gordon, J. G. & Gray, H. B. Characterization of oligomers of tetrakis(phenyl isocyanide)rhodium(i) in acetonitrile solution. J. Am. Chem. Soc. 97, 3553–3555 (1975).
Mann, K. R., Lewis, N. S., Williams, R. M., Gray, H. B. & Gordon, J. G. Further studies of metal-metal bonded oligomers of rhodium(i) isocyanide complexes. Crystal structure analysis of octakis(phenyl isocyanide)dirhodium bis(tetraphenylborate). Inorg. Chem. 17, 828–834 (1978).
King, K. A., Spellane, P. J. & Watts, R. J. Excited-state properties of a triply ortho-metalated iridium(iii) complex. J. Am. Chem. Soc. 107, 1431–1432 (1985).
Roundhill, D. M., Gray, H. B. & Che, C. M. Pyrophosphito-bridged diplatinum chemistry. Acc. Chem. Res. 22, 55–61 (1989).
Che, C.-M., Wan, K.-T., He, L.-Y., Poon, C.-K. & Yam, V. W.-W. Novel luminescent platinum(ii) complexes. Photophysics and photochemistry of Pt(5,5ʹ-Me2bpy)(CN)2(5,5ʹ-Me2bpy=5,5ʹ-dimethyl-2,2ʹ-bipyridine). J. Chem. Soc. Chem. Commun. 943–944 (1989).
Miskowski, V. M. & Houlding, V. H. Electronic spectra and photophysics of platinum(ii) complexes with α-diimine ligands. Solid-state effects. 1. Monomers and ligand π dimers. Inorg. Chem. 28, 1529–1533 (1989).
Kirk, A. D. Photochemistry and photophysics of chromium(iii) complexes. Chem. Rev. 99, 1607–1640 (1999).
Indelli, M. T., Chiorboli, C. & Scandola, F. Photochemistry and photophysics of coordination compounds: rhodium. Top. Curr. Chem. 280, 215–255 (2007).
Campagna, S., Puntoriero, F., Nastasi, F., Bergamini, G. & Balzani, V. Photochemistry and photophysics of coordination compounds: ruthenium. Top. Curr. Chem. 280, 117–214 (2007).
Wong, K. M.-C., Au, V. K.-M. & Yam, V. W.-W. in Comprehensive Inorganic Chemistry II 2nd edn Vol. 8 (Vol. ed. Yam, V. W.-W.; Series eds Reedijk, J. & Poeppelmeier, K.) 59–130 (Elsevier, 2013).
Yam, V. W.-W., Au, V. K.-M. & Leung, S. Y.-L. Light-emitting self-assembled materials based on d8 and d10 transition metal complexes. Chem. Rev. 115, 7589–7728 (2015).
Gersten, S. W., Samuels, G. J. & Meyer, T. J. Catalytic oxidation of water by an oxo-bridged ruthenium dimer. J. Am. Chem. Soc. 104, 4029–4030 (1982).
Büldt, L. A. & Wenger, O. S. Chromium complexes for luminescence, solar cells, photoredox catalysis, upconversion, and phototriggered NO release. Chem. Sci. 8, 7359–7367 (2017).
Baldo, M. A. et al. Highly efficient phosphorescent emission from organic electroluminescent devices. Nature 395, 151–154 (1998).
O’Regan, B. & Grätzel, M. A low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO2 films. Nature 353, 737–740 (1991).
Chi, Y. & Chou, P.-T. Transition-metal phosphors with cyclometalating ligands: fundamentals and applications. Chem. Soc. Rev. 39, 638–655 (2010).
Yang, C.-H. et al. Deep-blue-emitting heteroleptic iridium(iii) complexes suited for highly efficient phosphorescent OLEDs. Chem. Mater. 24, 3684–3695 (2012).
Tang, M.-C., Chan, A. K.-W., Chan, M.-Y. & Yam, V. W.-W. Platinum and gold complexes for OLEDs. Top. Curr. Chem. 374, 46 (2016).
Hamze, R. et al. Eliminating nonradiative decay in Cu(i) emitters: >99% quantum efficiency and microsecond lifetime. Science 363, 601–606 (2019).
Grätzel, M. Recent advances in sensitized mesoscopic solar cells. Acc. Chem. Res. 42, 1788–1798 (2009).
Tamayo, A. B. et al. Synthesis and characterization of facial and meridional tris-cyclometalated iridium(iii) complexes. J. Am. Chem. Soc. 125, 7377–7387 (2003).
Yam, V. W.-W. & Wong, K. M.-C. Luminescent metal complexes of d6, d8 and d10 transition metal centres. Chem. Commun. 47, 11579–11592 (2011).
Lo, S.-C., Namdas, E. B., Burn, P. L. & Samuel, I. D. W. Synthesis and properties of highly efficient electroluminescent green phosphorescent iridium cored dendrimers. Macromolecules 36, 9721–9730 (2003).
Wong, K. M.-C., Chan, M. M.-Y. & Yam, V. W.-W. Supramolecular assembly of metal-ligand chromophores for sensing and phosphorescent OLED applications. Adv. Mater. 26, 5558–5568 (2014).
Pinto, M. A. F. D. R. et al. A novel di-platinum(ii) octaphosphite complex showing metal–metal bonding and intense luminescence; a potential probe for basic proteins. X-ray crystal and molecular structure. J. Chem. Soc. Chem. Commun. https://doi.org/10.1039/C39800000013 (1980).
Dorn, M. et al. A vanadium(iii) complex with blue and NIR-II spin-flip luminescence in solution. J. Am. Chem. Soc. 142, 7947–7955 (2020).
Otto, S. et al. [Cr(ddpd)2]3+: a molecular, water-soluble, highly NIR-emissive ruby analogue. Angew. Chem. Int. Ed. 54, 11572–11576 (2015).
Wenger, O. S. Photoactive complexes with earth-abundant metals. J. Am. Chem. Soc. 140, 13522–13533 (2018).
Chábera, P. et al. A low-spin Fe(iii) complex with 100-ps ligand-to-metal charge transfer photoluminescence. Nature 543, 695–699 (2017).
Kjær, K. S. et al. Luminescence and reactivity of a charge-transfer excited iron complex with nanosecond lifetime. Science 363, 249–253 (2019).
Pal, A. K., Li, C., Hanan, G. S. & Zysman-Colman, E. Blue-emissive cobalt(iii) complexes and their use in the photocatalytic trifluoromethylation of polycyclic aromatic hydrocarbons. Angew. Chem. Int. Ed. 57, 8027–8031 (2018).
Wong, Y.-S., Tang, M.-C., Ng, M. & Yam, V. W.-W. Toward the design of phosphorescent emitters of cyclometalated earth-abundant nickel(ii) and their supramolecular study. J. Am. Chem. Soc. 142, 7638–7646 (2020).
Blaskie, M. W. & McMillin, D. R. Photostudies of copper(i) systems. 6. Room-temperature emission and quenching studies of bis(2,9-dimethyl-1,10-phenanthroline)copper(i). Inorg. Chem. 19, 3519–3522 (1980).
Deaton, J. C. et al. E-type delayed fluorescence of a phosphine-supported Cu2(μ-NAr2)2 diamond core: harvesting singlet and triplet excitons in OLEDs. J. Am. Chem. Soc. 132, 9499–9508 (2010).
Czerwieniec, R., Yu, J. & Yersin, H. Blue-light emission of Cu(i) complexes and singlet harvesting. Inorg. Chem. 50, 8293–8301 (2011).
Büldt, L. A., Larsen, C. B. & Wenger, O. S. Luminescent Ni0 diisocyanide chelates as analogues of CuI diimine complexes. Chem. Eur. J. 23, 8577–8580 (2017).
Romanov, A. S. et al. Dendritic carbene metal carbazole complexes as photoemitters for fully solution-processed OLEDs. Chem. Mater. 31, 3613–3623 (2019).
Shi, S. et al. Highly efficient photo- and electroluminescence from two-coordinate Cu(i) complexes featuring nonconventional N-heterocyclic carbenes. J. Am. Chem. Soc. 141, 3576–3588 (2019).
Yam, V. W.-W. & Lo, K. K.-W. Luminescent polynuclear d10 metal complexes. Chem. Soc. Rev. 28, 323–334 (1999).
Raptis, R. G. & Fackler, J. P. Structure of tris(μ-3,5-diphenylpyrazolato-N,Nʹ)tricopper(i). Structural comparisons with the silver(i) and gold(i) pyrazolate trimers. Inorg. Chem. 27, 4179–4182 (1988).
Yam, V. W.-W., Fung, W. K.-M. & Cheung, K.-K. Synthesis, structure, photophysics, and excited-state redox properties of the novel luminescent tetranuclear acetylidocopper(i) complex [Cu4(μ-dppm)4(μ4-η1,η2-C≡C-)](BF4)2. Angew. Chem. Int. Ed. 35, 1100–1102 (1996).
Lo, W.-Y. et al. Synthesis, photophysics, electrochemistry, theoretical, and transient absorption studies of luminescent copper(i) and silver(i) diynyl complexes. X-ray crystal structures of [Cu3(μ-dppm)3(μ3-η1-C≡CC≡CPh)2]PF6 and [Cu3(μ-dppm)3(μ3-η1-C≡CC≡CH)2]PF6. J. Am. Chem. Soc. 126, 7300–7310 (2004).
Zhan, S.-Z. et al. A luminescent edge-interlocked prismatic heteroleptic metallocage assembled through a ligand replacement reaction. Chem. Commun. 55, 11992–11995 (2019).
Lo, K. K.-W. Luminescent rhenium(i) and iridium(iii) polypyridine complexes as biological probes, imaging reagents, and photocytotoxic agents. Acc. Chem. Res. 48, 2985–2995 (2015).
Wang, S.-W. et al. Panchromatic Ru(ii) sensitizers bearing single thiocyanate for high efficiency dye sensitized solar cells. J. Mater. Chem. A 2, 17618–17627 (2014).
Sun, L., Hammarström, L., Åkermark, B. & Styring, S. Towards artificial photosynthesis: ruthenium–manganese chemistry for energy production. Chem. Soc. Rev. 30, 36–49 (2001).
Blakemore, J. D. et al. Half-sandwich iridium complexes for homogeneous water-oxidation catalysis. J. Am. Chem. Soc. 132, 16017–16029 (2010).
Blakemore, J. D., Crabtree, R. H. & Brudvig, G. W. Molecular catalysts for water oxidation. Chem. Rev. 115, 12974–13005 (2015).
Ko, C.-C. & Yam, V. W.-W. Coordination compounds with photochromic ligands: ready tunability and visible light-sensitized photochromism. Acc. Chem. Res. 51, 149–159 (2018).
Gao, F. G. & Bard, A. J. Solid-state organic light-emitting diodes based on tris(2,2ʹ-bipyridine)ruthenium(ii) complexes. J. Am. Chem. Soc. 122, 7426–7427 (2000).
Welter, S., Brunner, K., Hofstraat, J. W. & De Cola, L. Electroluminescent device with reversible switching between red and green emission. Nature 421, 54–57 (2003).
Miao, W. & Bard, A. J. Electrogenerated chemiluminescence. 72. Determination of immobilized DNA and C-reactive protein on Au(111) electrodes using tris(2,2ʹ-bipyridyl)ruthenium(ii) labels. Anal. Chem. 75, 5825–5834 (2003).
Tokel-Takvoryan, N. E., Hemingway, R. E. & Bard, A. J. Electrogenerated chemiluminescence. XIII. Electrochemical and electrogenerated chemiluminescence studies of ruthenium chelates. J. Am. Chem. Soc. 95, 6582–6589 (1973).
Yam, V. W.-W., Tang, R. P.-L., Wong, K. M.-C. & Cheung, K.-K. Synthesis, luminescence, electrochemistry, and ion-binding studies of platinum(ii) terpyridyl acetylide complexes. Organometallics 20, 4476–4482 (2001).
Wong, K. M.-C., Tang, W.-S., Lu, X.-X., Zhu, N. & Yam, V. W.-W. Functionalized platinum(ii) terpyridyl alkynyl complexes as colorimetric and luminescence pH sensors. Inorg. Chem. 44, 1492–1498 (2005).
McGarrah, J. E., Kim, Y.-J., Hissler, M. & Eisenberg, R. Toward a molecular photochemical device: a triad for photoinduced charge separation based on a platinum diimine bis(acetylide) chromophore. Inorg. Chem. 40, 4510–4511 (2001).
Kwok, E. C.-H., Chan, M.-Y., Wong, K. M.-C., Lam, W. H. & Yam, V. W.-W. Functionalized alkynylplatinum(ii) polypyridyl complexes for use as sensitizers in dye-sensitized solar cells. Chem. Eur. J. 16, 12244–12254 (2010).
Keller, J. M. et al. Negative polaron and triplet exciton diffusion in organometallic “molecular wires”. J. Am. Chem. Soc. 133, 11289–11298 (2011).
Carsten, B. et al. Examining the effect of the dipole moment on charge separation in donor–acceptor polymers for organic photovoltaic applications. J. Am. Chem. Soc. 133, 20468–20475 (2011).
Gust, D., Moore, T. A. & Moore, A. L. Mimicking photosynthetic solar energy transduction. Acc. Chem. Res. 34, 40–48 (2001).
McCusker, J. K. Electronic structure in the transition metal block and its implications for light harvesting. Science 363, 484–488 (2019).
Wrighton, M. & Morse, D. L. Nature of the lowest excited state in tricarbonylchloro-1,10-phenanthrolinerhenium(i) and related complexes. J. Am. Chem. Soc. 96, 998–1003 (1974).
Wrighton, M. S., Morse, D. L. & Pdungsap, L. Intraligand lowest excited states in tricarbonylhalobis(styrylpyridine)rhenium(i) complexes. J. Am. Chem. Soc. 97, 2073–2079 (1975).
Hawecker, J., Lehn, J.-M. & Ziessel, R. Electrocatalytic reduction of carbon dioxide mediated by Re(bipy)(CO)3Cl (bipy=2,2ʹ-bipyridine). J. Chem. Soc. Chem. Commun. https://doi.org/10.1039/C39840000328 (1984).
Takeda, H., Koike, K., Inoue, H. & Ishitani, O. Development of an efficient photocatalytic system for CO2 reduction using rhenium(i) complexes based on mechanistic studies. J. Am. Chem. Soc. 130, 2023–2031 (2008).
Sekizawa, K., Maeda, K., Domen, K., Koike, K. & Ishitani, O. Artificial Z-scheme constructed with a supramolecular metal complex and semiconductor for the photocatalytic reduction of CO2. J. Am. Chem. Soc. 135, 4596–4599 (2013).
Wenger, O. S. Proton-coupled electron transfer with photoexcited metal complexes. Acc. Chem. Res. 46, 1517–1526 (2013).
Yella, A. et al. Porphyrin-sensitized solar cells with cobalt(ii/iii)–based redox electrolyte exceed 12 percent efficiency. Science 334, 629–634 (2011).
Mathew, S. et al. Dye-sensitized solar cells with 13% efficiency achieved through the molecular engineering of porphyrin sensitizers. Nat. Chem. 6, 242–247 (2014).
Li, G., Mark, M. F., Lv, H., McCamant, D. W. & Eisenberg, R. Rhodamine-platinum diimine dithiolate complex dyads as efficient and robust photosensitizers for light-driven aqueous proton reduction to hydrogen. J. Am. Chem. Soc. 140, 2575–2586 (2018).
Lee, S.-H. et al. Design and synthesis of bipyridine platinum(ii) bisalkynyl fullerene donor–chromophore–acceptor triads with ultrafast charge separation. J. Am. Chem. Soc. 136, 10041–10052 (2014).
Cummings, S. D. & Eisenberg, R. Tuning the excited-state properties of platinum(ii) diimine dithiolate complexes. J. Am. Chem. Soc. 118, 1949–1960 (1996).
McMillin, D. R. & Moore, J. J. Luminescence that lasts from Pt(trpy)Cl+ derivatives (trpy=2,2ʹ;6ʹ,2ʹʹ-terpyridine). Coord. Chem. Rev. 229, 113–121 (2002).
Wong, K. M.-C. & Yam, V. W.-W. Self-assembly of luminescent alkynylplatinum(ii) terpyridyl complexes: modulation of photophysical properties through aggregation behavior. Acc. Chem. Res. 44, 424–434 (2011).
Yam, V. W.-W., Wong, K. M.-C. & Zhu, N. Solvent-induced aggregation through metal···metal/π···π interactions: large solvatochromism of luminescent organoplatinum(ii) terpyridyl complexes. J. Am. Chem. Soc. 124, 6506–6507 (2002).
Yu, C., Wong, K. M.-C., Chan, K. H.-Y. & Yam, V. W.-W. Polymer-induced self-assembly of alkynylplatinum(ii) terpyridyl complexes by metal⋅⋅⋅metal/π⋅⋅⋅π interactions. Angew. Chem. Int. Ed. 44, 791–794 (2005).
Tam, A. Y.-Y., Wong, K. M.-C. & Yam, V. W.-W. Unusual luminescence enhancement of metallogels of alkynylplatinum(ii) 2,6-bis(N-alkylbenzimidazol-2ʹ-yl)pyridine complexes upon a gel-to-sol phase transition at elevated temperatures. J. Am. Chem. Soc. 131, 6253–6260 (2009).
Chan, K. H.-Y., Chow, H.-S., Wong, K. M.-C., Yeung, M. C.-L. & Yam, V. W.-W. Towards thermochromic and thermoresponsive near-infrared (NIR) luminescent molecular materials through the modulation of inter- and/or intramolecular Pt⋯Pt and π–π interactions. Chem. Sci. 1, 477–482 (2010).
Po, C., Tam, A. Y.-Y., Wong, K. M.-C. & Yam, V. W.-W. Supramolecular self-assembly of amphiphilic anionic platinum(ii) complexes: a correlation between spectroscopic and morphological properties. J. Am. Chem. Soc. 133, 12136–12143 (2011).
Leung, S. Y.-L., Tam, A. Y.-Y., Tao, C.-H., Chow, H. S. & Yam, V. W.-W. Single-turn helix–coil strands stabilized by metal···metal and π–π interactions of the alkynylplatinum(ii) terpyridyl moieties in meta-phenylene ethynylene foldamers. J. Am. Chem. Soc. 134, 1047–1056 (2012).
Chung, C. Y.-S., Li, S. P.-Y., Louie, M.-W., Lo, K. K.-W. & Yam, V. W.-W. Induced self-assembly and disassembly of water-soluble alkynylplatinum(ii) terpyridyl complexes with “switchable” near-infrared (NIR) emission modulated by metal–metal interactions over physiological pH: demonstration of pH-responsive NIR luminescent probes in cell-imaging studies. Chem. Sci. 4, 2453–2462 (2013).
Au-Yeung, H.-L., Leung, S. Y.-L., Tam, A. Y.-Y. & Yam, V. W.-W. Transformable nanostructures of platinum-containing organosilane hybrids: non-covalent self-assembly of polyhedral oligomeric silsesquioxanes assisted by Pt···Pt and π–π stacking interactions of alkynylplatinum(ii) terpyridine moieties. J. Am. Chem. Soc. 136, 17910–17913 (2014).
Zhang, K., Yeung, M. C.-L., Leung, S. Y.-L. & Yam, V. W.-W. Manipulation of nanostructures in the co-assembly of platinum(ii) complexes and block copolymers. Chem 2, 825–839 (2017).
Chen, Z., Chan, A. K.-W., Wong, V. C.-H. & Yam, V. W.-W. A supramolecular strategy toward an efficient and selective capture of platinum(ii) complexes. J. Am. Chem. Soc. 141, 11204–11211 (2019).
Chan, M. H.-Y., Leung, S. Y.-L. & Yam, V. W.-W. Rational design of multi-stimuli-responsive scaffolds: synthesis of luminescent oligo(ethynylpyridine)-containing alkynylplatinum(ii) polypyridine foldamers stabilized by Pt···Pt interactions. J. Am. Chem. Soc. 141, 12312–12321 (2019).
Ai, Y. et al. A platinum(ii) molecular hinge with motions visualized by phosphorescence changes. Proc. Natl Acad. Sci. USA 116, 13856–13861 (2019).
Zhang, K., Yeung, M. C.-L., Leung, S. Y.-L. & Yam, V. W.-W. Energy landscape in supramolecular coassembly of platinum(ii) complexes and polymers: morphological diversity, transformation, and dilution stability of nanostructures. J. Am. Chem. Soc. 140, 9594–9605 (2018).
Leung, S. Y.-L., Wong, K. M.-C. & Yam, V. W.-W. Self-assembly of alkynylplatinum(ii) terpyridine amphiphiles into nanostructures via steric control and metal–metal interactions. Proc. Natl Acad. Sci. USA 113, 2845–2850 (2016).
Kato, M., Omura, A., Toshikawa, A., Kishi, S. & Sugimoto, Y. Vapor-induced luminescence switching in crystals of the syn isomer of a dinuclear (bipyridine)platinum(ii) complex bridged with pyridine-2-thiolate ions. Angew. Chem. Int. Ed. 41, 3183–3185 (2002).
Krikorian, M., Liu, S. & Swager, T. M. Columnar liquid crystallinity and mechanochromism in cationic platinum(ii) complexes. J. Am. Chem. Soc. 136, 2952–2955 (2014).
Aliprandi, A., Mauro, M. & De Cola, L. Controlling and imaging biomimetic self-assembly. Nat. Chem. 8, 10–15 (2016).
Chen, Z. & Yam, V. W.-W. Precise size-selective sieving of nanoparticles using a highly oriented two-dimensional supramolecular polymer. Angew. Chem. Int. Ed. 59, 4840–4845 (2020).
Chakrabarty, R., Mukherjee, P. S. & Stang, P. J. Supramolecular coordination: self-assembly of finite two- and three-dimensional ensembles. Chem. Rev. 111, 6810–6918 (2011).
Sommer, R. D., Rheingold, A. L., Goshe, A. J. & Bosnich, B. Supramolecular chemistry: molecular recognition and self-assembly using rigid spacer-chelators bearing cofacial terpyridyl palladium(ii) complexes separated by 7 Å. J. Am. Chem. Soc. 123, 3940–3952 (2001).
Chan, A. K.-W. & Yam, V. W.-W. Precise modulation of molecular building blocks from tweezers to rectangles for recognition and stimuli-responsive processes. Acc. Chem. Res. 51, 3041–3051 (2018).
Tanaka, Y., Wong, K. M.-C. & Yam, V. W.-W. Phosphorescent molecular tweezers based on alkynylplatinum(ii) terpyridine system: turning on of NIR emission via heterologous Pt⋯M interactions (M=PtII, PdII, AuIII and AuI). Chem. Sci. 3, 1185–1191 (2012).
Tanaka, Y., Wong, K. M.-C. & Yam, V. W.-W. Host–guest interactions of phosphorescent molecular tweezers based on an alkynylplatinum(ii) terpyridine system with polyaromatic hydrocarbons. Chem. Eur. J. 19, 390–399 (2013).
Tanaka, Y., Wong, K. M.-C. & Yam, V. W.-W. Platinum-based phosphorescent double-decker tweezers: a strategy for extended heterologous metal–metal interactions. Angew. Chem. Int. Ed. 52, 14117–14120 (2013).
Magnus, G. Magnus’ green salt. Pogg. Ann. 14, 239–242 (1828).
Debije, M. G. et al. Optoelectronic properties of quasi-linear, self-assembled platinum complexes: Pt–Pt distance dependence. Adv. Funct. Mater. 14, 323–328 (2004).
Kong, F. K.-W., Chan, A. K.-W., Ng, M., Low, K.-H. & Yam, V. W.-W. Construction of discrete pentanuclear platinum(ii) stacks with extended metal–metal interactions by using phosphorescent platinum(ii) tweezers. Angew. Chem. Int. Ed. 56, 15103–15107 (2017).
Chan, A. K.-W., Lam, W. H., Tanaka, Y., Wong, K. M.-C. & Yam, V. W.-W. Multiaddressable molecular rectangles with reversible host–guest interactions: modulation of pH-controlled guest release and capture. Proc. Natl Acad. Sci. USA 112, 690–695 (2015).
Constable, E. C., Henney, R. P. G., Leese, T. A. & Tocher, D. A. Cyclopalladated and cycloplatinated complexes of 6-phenyl-2,2ʹ-bipyridine: platinum-platinum interactions in the solid state. J. Chem. Soc. Chem. Commun. 513–515 (1990).
Brooks, J. et al. Synthesis and characterization of phosphorescent cyclometalated platinum complexes. Inorg. Chem. 41, 3055–3066 (2002).
Lu, W. et al. Light-emitting tridentate cyclometalated platinum(ii) complexes containing σ-alkynyl auxiliaries: tuning of photo- and electrophosphorescence. J. Am. Chem. Soc. 126, 4958–4971 (2004).
Fleetham, T., Li, G., Wen, L. & Li, J. Efficient “pure” blue OLEDs employing tetradentate Pt complexes with a narrow spectral bandwidth. Adv. Mater. 26, 7116–7121 (2014).
Maestri, M. et al. Luminescence of ortho-metallated platinum(ii) complexes. Chem. Phys. Lett. 122, 375–379 (1985).
Barigelletti, F. et al. Temperature dependence of the luminescence of cyclometalated palladium(ii), rhodium(iii), platinum(ii), and platinum(iv) complexes. Inorg. Chem. 27, 3644–3647 (1988).
Cocchi, M., Virgili, D., Fattori, V., Rochester, D. L. & Williams, J. A. G. N^C^N-coordinated platinum(ii) complexes as phosphorescent emitters in high-performance organic light-emitting devices. Adv. Funct. Mater. 17, 285–289 (2007).
Yersin, H., Rausch, A. F., Czerwieniec, R., Hofbeck, T. & Fischer, T. The triplet state of organo-transition metal compounds. Triplet harvesting and singlet harvesting for efficient OLEDs. Coord. Chem. Rev. 255, 2622–2652 (2011).
Tam, A. Y.-Y., Tsang, D. P.-K., Chan, M.-Y., Zhu, N. & Yam, V. W.-W. A luminescent cyclometalated platinum(ii) complex and its green organic light emitting device with high device performance. Chem. Commun. 47, 3383–3385 (2011).
Kui, S. C. F. et al. Luminescent organoplatinum(ii) complexes with functionalized cyclometalated C^N^C ligands: structures, photophysical properties, and material applications. Chem. Eur. J. 18, 96–109 (2012).
Baldo, M. A., Lamansky, S., Burrows, P. E., Thompson, M. E. & Forrest, S. R. Very high-efficiency green organic light-emitting devices based on electrophosphorescence. Appl. Phys. Lett. 75, 4–6 (1999).
Lam, E. S.-H. et al. Luminescent platinum(ii) complexes of 1,3-bis(N-alkylbenzimidazol-2ʹ-yl)benzene-type ligands with potential applications in efficient organic light-emitting diodes. Chem. Eur. J. 19, 6385–6397 (2013).
Chan, A. K.-W. et al. Synthesis and characterization of luminescent cyclometalated platinum(ii) complexes of 1,3-bis-hetero-azolylbenzenes with tunable color for applications in organic light-emitting devices through extension of π conjugation by variation of the heteroatom. Chem. Eur. J. 19, 13910–13924 (2013).
Kong, F. K.-W., Tang, M.-C., Wong, Y.-C., Chan, M.-Y. & Yam, V. W.-W. Design strategy for high-performance dendritic carbazole-containing alkynylplatinum(ii) complexes and their application in solution-processable organic light-emitting devices. J. Am. Chem. Soc. 138, 6281–6291 (2016).
Yam, V. W.-W., Wong, K. M.-C., Hung, L.-L. & Zhu, N. Luminescent gold(iii) alkynyl complexes: synthesis, structural characterization, and luminescence properties. Angew. Chem. Int. Ed. 44, 3107–3110 (2005).
Wong, K. M.-C. et al. A novel class of phosphorescent gold(iii) alkynyl-based organic light-emitting devices with tunable colour. Chem. Commun. https://doi.org/10.1039/b503315b (2005).
Au, V. K.-M. et al. High-efficiency green organic light-emitting devices utilizing phosphorescent bis-cyclometalated alkynylgold(iii) complexes. J. Am. Chem. Soc. 132, 14273–14278 (2010).
Tang, M.-C., Tsang, D. P.-K., Chan, M. M.-Y., Wong, K. M.-C. & Yam, V. W.-W. Dendritic luminescent gold(iii) complexes for highly efficient solution-processable organic light-emitting devices. Angew. Chem. Int. Ed. 52, 446–449 (2013).
Wong, B. Y.-W., Wong, H.-L., Wong, Y.-C., Chan, M.-Y. & Yam, V. W.-W. Versatile synthesis of luminescent tetradentate cyclometalated alkynylgold(iii) complexes and their application in solution-processable organic light-emitting devices. Angew. Chem. Int. Ed. 56, 302–305 (2017).
Lee, C.-H. et al. Isomeric tetradentate ligand-containing cyclometalated gold(iii) complexes. J. Am. Chem. Soc. 142, 520–529 (2020).
Tang, M.-C. et al. Highly emissive fused heterocyclic alkynylgold(iii) complexes for multiple color emission spanning from green to red for solution-processable organic light-emitting devices. Angew. Chem. Int. Ed. 57, 5463–5466 (2018).
Tang, M.-C. et al. Versatile design strategy for highly luminescent vacuum-evaporable and solution-processable tridentate gold(iii) complexes with monoaryl auxiliary ligands and their applications for phosphorescent organic light emitting devices. J. Am. Chem. Soc. 139, 9341–9349 (2017).
Yam, V. W.-W., Choi, S. W.-K., Lai, T.-F. & Lee, W.-K. Syntheses, crystal structures and photophysics of organogold(iii) diimine complexes. J. Chem. Soc. Dalton Trans. https://doi.org/10.1039/DT9930001001 (1993).
Tang, M.-C. et al. Realization of thermally stimulated delayed phosphorescence in arylgold(iii) complexes and efficient gold(iii) based blue-emitting organic light-emitting devices. J. Am. Chem. Soc. 140, 13115–13124 (2018).
Leung, M.-Y. et al. Thermally stimulated delayed phosphorescence (TSDP)-based gold(iii) complexes of tridentate pyrazine-containing pincer ligand with wide emission color tunability and their application in organic light-emitting devices. J. Am. Chem. Soc. 142, 2448–2459 (2020).
Li, L.-K. et al. Strategies towards rational design of gold(iii) complexes for high-performance organic light-emitting devices. Nat. Photonics 13, 185–191 (2019).
Kwok, W.-K. et al. Judicious choice of N-heterocycles for the realization of sky-blue- to green-emitting carbazolylgold(iii) C^C^N complexes and their applications for organic light-emitting devices. Angew. Chem. Int. Ed. https://doi.org/10.1002/anie.202001972 (2020).
To, W.-P. et al. Highly luminescent pincer gold(iii) aryl emitters: thermally activated delayed fluorescence and solution-processed OLEDs. Angew. Chem. Int. Ed. 56, 14036–14041 (2017).
Zhou, D. et al. Thermally stable donor–acceptor type (alkynyl)gold(iii) TADF emitters achieved EQEs and luminance of up to 23.4% and 70 300 cd m−2 in vacuum-deposited OLEDs. Adv. Sci. 6, 1802297 (2019).
Beucher, H. et al. Highly efficient green solution processable organic light-emitting diodes based on a phosphorescent κ3-(N^C^C)gold(iii)-alkynyl complex. Chem. Mater. 32, 1605–1611 (2020).
Sawa, A. Resistive switching in transition metal oxides. Mater. Today 11, 28–36 (2008).
Cho, B., Song, S., Ji, Y., Kim, T.-W. & Lee, T. Organic resistive memory devices: performance enhancement, integration, and advanced architectures. Adv. Funct. Mater. 21, 2806–2829 (2011).
Lin, W.-P., Liu, S.-J., Gong, T., Zhao, Q. & Huang, W. Polymer-based resistive memory materials and devices. Adv. Mater. 26, 570–606 (2014).
Wang, P. et al. Thermoresponsive memory behavior in metallosupramolecular polymer-based ternary memory devices. ACS Appl. Mater. Interfaces 9, 32930–32938 (2017).
Hwang, B., Gu, C., Lee, D. & Lee, J.-S. Effect of halide-mixing on the switching behaviors of organic-inorganic hybrid perovskite memory. Sci. Rep. 7, 43794 (2017).
Li, B. et al. Metal halide perovskites for resistive switching memory devices and artificial synapses. J. Mater. Chem. C. 7, 7476–7493 (2019).
Fang, J., You, H., Chen, J., Lin, J. & Ma, D. Memory devices based on lanthanide (Sm3+, Eu3+, Gd3+) complexes. Inorg. Chem. 45, 3701–3704 (2006).
Pradhan, B. & Das, S. Role of new bis(2,2ʹ-bipyridyl)(triazolopyridyl)ruthenium(ii) complex in the organic bistable memory application. Chem. Mater. 20, 1209–1211 (2008).
Paul, N. D., Rana, U., Goswami, S., Mondal, T. K. & Goswami, S. Azo anion radical complex of rhodium as a molecular memory switching device: isolation, characterization, and evaluation of current–voltage characteristics. J. Am. Chem. Soc. 134, 6520–6523 (2012).
Goswami, S., Sengupta, D., Paul, N. D., Mondal, T. K. & Goswami, S. Redox non-innocence of coordinated 2-(arylazo) pyridines in iridium complexes: characterization of redox series and an insight into voltage-induced current characteristics. Chem. Eur. J. 20, 6103–6111 (2014).
Au, V. K.-M., Wu, D. & Yam, V. W.-W. Organic memory devices based on a bis-cyclometalated alkynylgold(iii) complex. J. Am. Chem. Soc. 137, 4654–4657 (2015).
Hong, E. Y.-H., Poon, C.-T. & Yam, V. W.-W. A phosphole oxide-containing organogold(iii) complex for solution-processable resistive memory devices with ternary memory performances. J. Am. Chem. Soc. 138, 6368–6371 (2016).
Leung, M.-Y., Leung, S. Y.-L., Wu, D., Yu, T. & Yam, V. W.-W. Synthesis, electrochemistry, and photophysical studies of ruthenium(ii) polypyridine complexes with D–π–A–π–D type ligands and their application studies as organic memories. Chem. Eur. J. 22, 14013–14021 (2016).
Chan, H., Lee, S.-H., Poon, C.-T., Ng, M. & Yam, V. W.-W. Manipulation of push–pull system by functionalization of porphyrin at β-position for high-performance solution-processable ternary resistive memory devices. ChemNanoMat 3, 164–167 (2017).
Hong, E. Y.-H. & Yam, V. W.-W. Triindole-tris-alkynyl-bridged trinuclear gold(i) complexes for cooperative supramolecular self-assembly and small-molecule solution-processable resistive memories. ACS Appl. Mater. Interfaces 9, 2616–2624 (2017).
Chan, A. K.-W. et al. Synthesis and characterization of luminescent cyclometalated platinum(ii) complexes with tunable emissive colors and studies of their application in organic memories and organic light-emitting devices. J. Am. Chem. Soc. 139, 10750–10761 (2017).
Li, Y. et al. Supramolecular self-assembly and dual-switch vapochromic, vapoluminescent, and resistive memory behaviors of amphiphilic platinum(ii) complexes. J. Am. Chem. Soc. 139, 13858–13866 (2017).
Chan, H., Wong, H.-L., Ng, M., Poon, C.-T. & Yam, V. W.-W. Switching of resistive memory behavior from binary to ternary logic via alteration of substituent positioning on the subphthalocyanine core. J. Am. Chem. Soc. 139, 7256–7263 (2017).
V.W.-W.Y. acknowledges support from the University of Hong Kong under the University Research Committee Strategically Oriented Research Theme on Functional Materials for Molecular Electronics. This work was supported by a General Research Fund grant from the Research Grants Council of Hong Kong Special Administrative Region, People’s Republic of China (HKU 17306219). The authors acknowledge M. H.-Y. Chan and Y.-H. Cheng for their technical assistance in the preparation of the final version of the manuscript.
The authors declare no competing interests.
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
About this article
Cite this article
Yam, V.WW., Chan, A.KW. & Hong, E.YH. Charge-transfer processes in metal complexes enable luminescence and memory functions. Nat Rev Chem 4, 528–541 (2020). https://doi.org/10.1038/s41570-020-0199-7
This article is cited by
Synthesis, Characterization of Metal Complexes with Azo Ligand Containing Indole Ring and Study of Palladium Complex Activity Against Leukemia
Arabian Journal for Science and Engineering (2023)
Diving into the optoelectronic properties of Cu(II) and Zn(II) curcumin complexes: a DFT and wavefunction benchmark
Journal of Molecular Modeling (2023)
Manipulating electron redistribution to achieve electronic pyroelectricity in molecular [FeCo] crystals
Nature Communications (2021)
Nature Chemistry (2021)
Nano Research (2021)