Editorial for the ACS Select Virtual Issue on Emerging Investigators in

Editorial pubs.acs.org/IC

Editorial for the ACS Select Virtual Issue on Emerging Investigators in Inorganic Photochemistry and Photophysics

T

synthetic techniques, making it possible to continuously inspire creativity in the realm of inorganic photochemistry. In the original report on fac-Ir(ppy)3, where ppy = 2phenylpyridine, Watts and co-workers described this MLCT chromophore as a potential photosensitizer.12 However, it was not until 15 years later that the groups of Mark Thompson at University of Southern California and Steve Forrest at Princeton University recognized that the brilliant green solidstate emission properties of this complex could be exploited in efficient “organic” light-emitting diodes (OLEDs) capitalizing on triplet-state photoluminescence.13 In the present day, these and related molecules can be found in numerous OLED-based display devices and currently represent a massive worldwide R&D effort.14 The research group of Thomas Teets at the University of Houston is interested in developing new triplet emitters based on heteroleptic mononuclear iridium(III) complexes. One class of molecules features bidentate ancillary ligands based on β-ketoiminate (acNacMe) and β-diketiminates (NacNacR) supported on bis-cyclometalating templates, Ir(C^N)2.15 One of the newly designed chromophores, Ir(bt)2(acNacMe), where bt = 2-phenylbenzothiazole, possesses a remarkably large photoluminescence quantum yield of 82% consistent with a bt-based ligand-localized triplet phosphorescence. Using a combination of four distinct cyclometalating ligands, in concert with three different aryl isocyanides, Teets and colleagues generated a series of 11 IrIII molecules with the generic molecular formula cis-Ir(C^N)2(CNArR)2.16 These complexes displayed a broad range of redox potentials with concomitant photoluminescence spectra from blue to orange. Another important class of inorganic chromophores relies on sensitized lanthanide photoluminescence, the subject of a recent virtual issue in this journal.17 The work of Rebecca Abergel at Lawrence Berkeley National Laboratory, Berkeley, CA, proposes that ligand-based photosensitization of lanthanide ions in molecular complexes can be successfully applied to solid-state lanthanide-containing nanocrystals.18 Initial efforts have proven successful in the generation of Eu3+ and Tb3+ photoluminescence in nanocrystals doped with these ions and coated with surface-bound UV-harvesting sensitizer ligands. The research group of Paul Elliott at the University of Huddersfield in the U.K. recently completed a photochemical reactivity study of ligand loss in the triazole-containing ruthenium(II) complex [Ru(pytz)(btz)2]2+, where pytz = 1benzyl-4-(pyrid-2-yl)-1,2,3-triazole and btz = 1,1′-dibenzyl-4,4′bi-1,2,3-triazolyl.19 In CH3CN solutions under photochemical activation (λex = 363 nm), this complex dechelates one of the bidentate btz ligands in a stepwise fashion, giving rise to the unusual complex trans-[Ru(pytz)(btz)(CH3CN)2]2+. Electronic structure calculations suggest that the lowest triplet excited state contains a significant amount of metal-centered (3MC) character, featuring a pseudo-four-coordinate 3MC state as

his virtual issue features recent contributions from 16 young investigators (Ph.D. degrees awarded in 2004 and subsequent years) working in inorganic photochemistry and photophysics. This research area is vast and varied, and thus this compilation only aims to capture a small slice of the diversity of this vibrant community and is by no means complete or intended to be comprehensive. All articles were selected from the journals Inorganic Chemistry, Journal of the American Chemical Society, Chemistry of Materials, ACS Catalysis, Journal of Physical Chemistry Letters, and ACS Energy Letters, largely in 2015 and 2016. While the overarching theme in these articles highlights the utilization, generation, and/or manipulation of photons, the scientific investigations range from fundamental in nature to discovery-based phenomena to focused applications. In this context, select d- and f-block elements form the basis for the photoactive component(s) under evaluation and include solid-state energy-relevant materials, designer surface-bound molecular assemblies, photomodulated materials, photosensitizer design, computational inorganic photochemistry, upconversion processes, solar fuels photochemistry, photoelectrochemistry, excited-state electronand energy-transfer reactions, molecular and materials photophysics, and chemical sensing. Although many observations related to inorganic photochemistry and photophysics were historically noted over the past several hundred years, systematic experimental studies began to appear in the 1950s, many of which were featured in the monograph of Balzani and Carassiti1 and a book edited by Adamson and Fleischauer.2 Some of the young contributors to this issue would likely recall the ethereal orange-red photoluminescence from solutions of [Ru(bpy)3]2+ being responsible for their original fascination with this field. Although this benchmark metal-to-ligand charge-transfer (MLCT) chromophore was originally synthesized in 1959,3 it was not until the early 1970s when Adamson and co-workers first recognized it as a photosensitizer.4,5 In the interim, Crosby and co-workers quantitatively evaluated the MLCT photoluminescence in [Ru(bpy)3]2+ and related chromophores,6−8 permitting the establishment of the original Jablonski diagrams that have withstood the test of time. Soon after, numerous reports emerged that clearly demonstrated excited-state electrontransfer and triplet energy-transfer photochemistry from [Ru(bpy)3]2+.9,10 These results suggested a myriad of energyrelevant applications, including water splitting,11 and one could argue that the rest is history. Modern inorganic photochemistry as we know it today was largely stimulated by these original reports and remains pervasive to date, currently transcending most scientific disciplines. Some of the research descriptions below certainly echo aspects from the modern time origin of this field, whereas others emulate a hybridization of diverse subjects brought together using inorganic chemistry concepts. All of the work featured here was enabled through the worldwide efforts of innumerable researchers that stimulated the development of the experimental, computational, and © 2016 American Chemical Society

Published: December 19, 2016 12483

DOI: 10.1021/acs.inorgchem.6b02830 Inorg. Chem. 2016, 55, 12483−12487

Inorganic Chemistry

Editorial

opposed to a 3MLCT excited state. Intramolecular photochemistry, namely, intramolecular triplet−triplet energy transfer, represents one subject of investigation in the research group of Benjamin Dietzek at Friedrich Schiller University, Jena, Germany. In a recent contribution, in collaboration with Ulrich Schubert, Dietzek and co-workers investigated ruthenium(II) terpyridyl complexes covalently linked to C60 moieties with systematically varied phenylene and phenylene−ethynylene− phenylene bridging subunits, revealing rapid energy-transfer kinetics.20 Similarly, in cyanide-bridged IrIII−RuII donor− acceptor complexes, deactivation of the IrIII MLCT excited state gave way to the formation of RuII MLCT-based photoluminescence in the red, consistent with efficient energy transfer.21 Interestingly, oxidation of RuII to RuIII revealed a broad intervalence charge-transfer band (Ir → Ru) in the nearIR consistent with a weakly coupled class II system in the Robin−Day classification.22 Alex Miller’s group at the University of North Carolina at Chapel Hill has dedicated a multiyear effort towards understanding the photocatalytic hydrogen evolution properties of [Cp*Ir(bpy)Cl]+ and related complexes in water. These molecules, first prepared by Raymond Ziessel in Strasbourg in 1989,23 are quite remarkable because they can behave as either excited-state proton or hydride donors depending upon the medium.24,25 Miller’s group first demonstrated that these molecules served as molecular photoelectrocatalysts at pH 7.026 and followed up this investigation by providing evidence of photochemical formic acid dehydrogenation from the same complexes.27 Detailed photochemical and photoluminescence quenching studies also revealed that [Cp*Ir(bpy)H]+ participates in a bimetallic self-quenching excited-state electrontransfer process, ultimately yielding dihydrogen (H2) in essentially quantitative yield, a completely unprecedented result.28 This excited-state electron-transfer reaction generates both a reduced and oxidized sensitizer that readily releases H2 in a photocatalytic manner in the presence of a proton source. New H2-releasing photocatalytic schemes can therefore now be envisioned as operating through excited-state self-quenching phenomena. Completely orthogonal to energy generation from water, aqueous solutions are routinely consumed in foods, beverages, and pharmaceutical products. Qiang Zhao from Nanjing University in China has developed a RuII MLCT complex bearing a styryl-containing substituent that selectively binds bisulfite ion (HSO3−),29 a common food additive that is extensively encountered as a pollutant in the environment. In phosphate-buffered saline, this complex selectively reacts with bisulfite by engaging in 1,4-Michael addition chemistry, dramatically modifying the UV−vis spectrum of the chromophore with a resulting color change from yellow to pink. This dosimeter behavior was successfully applied to the quantitative detection of bisulfite in both granulated and crystalline sugar samples. Elena Jakubikova, my colleague at North Carolina State University in Raleigh, NC, operates a unique research program in what can be best described as computational photochemistry. One major focus of her work involves the computer-aided design of FeII-based polypyridyl MLCT sensitizers to enable excited-state lifetime tuning for adaptation in dye-sensitized solar cells, for example.30−32 The detailed electronic structure insight provided through these computational investigations arms experimentalists with ligand structural elements to engineer desired excited-state decay pathways. Providing insight into how to control the ligand field strength and the various

spin-state transitions in FeII MLCT excited states can indeed lead to relevant photophysical and sensitization processes.33,34 Cristian Strassert’s research group at Westfȧilische WilhelmsUniversität Münster in Germany has studied the solid-state photophysical properties of a series of cationic square-planar platinum(II) complexes, featuring a tridentate triazole ligand and a lone chloride or cyanide ancillary ligand.35 Numerous self-assembled structures featuring PtII−PtII interactions were generated in powders and neat thin films through reprecipitation procedures, ultimately forming both microscopic and nanoscopic structures that were strongly photoluminescent in the cyano-bearing complexes. Michael Rose’s group at the University of Texas at Austin is also investigating inorganicbased photoluminescence in solid-state Cu 4I4 cuboids, supported by trialkylantimony donors.36 Because there are no aryl groups resident in this structure, the photophysics was exclusively attributed to the Cu4I4 moiety, where the Cu−Cu distances were relatively short [2.761(3) Å] in the lowtemperature crystal structure. The photoluminescence was strongly temperature-dependent, increasing sharply with decreasing temperature, which correlated with a decrease in the Cu−Cu distances with lower temperatures. The authors identified a crossing point in this thermoluminescent response, attenuating sharply when the Cu−Cu distance exceeded 2.80 Å. Liu and co-workers at the National University of Singapore have recently developed the epitaxial end-on synthesis of upconversion nanocrystals, consisting of various lanthanide activator species grown onto NaYF4 microrods.37 This strategy yields gram quantities of multicolor-banded single photoluminescent crystals that were shown to successfully serve as barcodes in anticounterfeit security inks and cell-tracking applications. Amanda Morris and her group at Virginia Tech in Blacksburg, VA, carried out a detailed study of Förster-type resonance energy transfer (FRET) occurring between identical RuII MLCT chromophores, which were postsynthetically appended in the metal−organic framework UiO-67.38 It should be noted that FRET has been shown to be operative in RuII MLCT molecules, serving as either donors or acceptors for various organic chromophores in solution.39−43 However, this investigation by Morris and colleagues quantitatively suggests that the dynamic self-quenching of the observed charge-transfer photoluminescence results exclusively from FRET in two and three dimensions. An important implication of this work is that FRET may be more widespread in materials incorporating MLCT excited states than originally thought, and this may be especially true in materials containing high concentrations of these chromophores in close proximity. Alexis Ostrowski, my former colleague at the Center for Photochemical Sciences at Bowling Green State University in Bowling Green, OH, has an interest in photocontrol of the mechanical properties of biomaterials and metal-containing polymers. One recent contribution from the Ostrowski group details a method for the photopatterning of preprepared polysaccharide-based hydrogels coordinated to FeIII.44 Upon 405 nm light exposure, FeIII is reduced to FeII with concomitant decarboxylation of the polysaccharide, resulting in significant changes to the mechanical properties of the material. Ostrowski and colleagues have also demonstrated complete reversibility in the mechanical strength of CrIII-containing metallosupramolecular polymers resulting from light activation.45 In essence, the excited state of the CrIII species results in dechelation from the polymer backbone and is sustained with continuous photostimulation, resulting in material softening; CrIII coor12484

DOI: 10.1021/acs.inorgchem.6b02830 Inorg. Chem. 2016, 55, 12483−12487

Inorganic Chemistry

Editorial

through two distinct mechanisms on mesoscopic TiO2, i.e., direct excitation of the acceptor chromophore and photochemical upconversion resulting from selective excitation of the platinum(II) porphyrin in the green. A classic quadratic-tolinear light power dependence was observed for the latter process57 (albeit manifested in the measured photocurrent for the first time), thus leaving little doubt that photochemical upconversion was responsible for sensitizing electron injection with visible-light excitation. The work showcased from these young investigators provides a glimpse into the current state-of-the-art in modern inorganic photochemistry and illustrates that the future of this community is indeed brilliant with photons. Please join me in viewing these wonderfully diverse worldwide scientific contributions from these emerging researchers.

dinates again in the absence of light, and the material regains its original storage modulus. These are just a few representative examples of new promising classes of optomechanical materials that are poised to emerge from this laboratory. Curtis Berlinguette and co-workers at the University of British Columbia in Vancouver, Canada, developed the concept that simple inorganic coordination complexes spin-coated onto substrates can be photolyzed with deep UV light (254 nm; ligand-to-metal charge-transfer excitation) to generate amorphous metal oxide films suitable for electrochemical-based water oxidation catalysis.46 In the two contributions featured here,46,47 detailed investigations of the oxygen evolution reaction (OER) on both amorphous iridium oxide and iron oxide films is assessed, and the former material remains one of the best OER catalysts reported to date. Tom Hamann and his group at Michigan State University in East Lansing, MI, used electrodeposition (ED) to prepare both planar and nanostructured hematite films from FeCl2 and compared their photoelectrochemical performance to that of planar atomic layer deposition (ALD)-produced hematite films.48 In all instances, the crystalline ED-produced films outperformed the ALD materials in the photoelectrochemical OER, a result that was attributed to enhanced hole transport and collection in the former materials. When modified with the established CoPi water oxidation catalyst,49 the resultant hematite electrodes produced some of the largest measured photocurrents to date, featuring hole collection efficiencies approaching unity. This latter approach truly represents a scalable strategy for solar water splitting. Gordana Dukovic’s research group at the University of Colorado in Boulder, CO, has been developing semiconductor nanomaterials important for solar energy conversion strategies. In a collaboration with the National Renewable Energy Laboratory, the Dukovic group examined electron-transfer kinetics using transient absorption spectroscopy in CdS nanorod−[FeFe]-hydrogenase hybrid materials.50 This work concluded that modifications of the CdS material would enable enhanced electron-transfer rates/quantum efficiencies and therefore result in improved H2 production yields at the enzyme. In a different contribution, Dukovic and co-workers developed the synthesis and provided the first detailed spectroscopic characterization of oxynitride nanocrystals solubilized in toluene.51 The resultant excited state in this material decays with complex kinetics but possesses a long component with a time constant of ∼30 μs, potentially relevant for solar energy conversion schemes and triplet exciton transfer.52 Ken Hanson’s team at Florida State University in Tallahassee, FL, has initiated a research program where photon upconversion based on sensitized triplet−triplet annihilation53,54 has been directly integrated into dye-sensitized solar cells. In recent work, the Hanson group used zinc(II)coordination-driven self-assembly processes on TiO2 to construct upconverting bilayers, wherein the surface-bound diphenylanthracene-based singlet excited state was poised for electron injection into the conduction band of the semiconductor.55 It was demonstrated that a photocurrent could indeed be generated from selective visible excitation of the metalated porphyrin located on the periphery of the bilayer, with photochemical upconversion representing the only viable mechanism. In a follow-up study earlier this year, Hanson and co-workers provided even more direct experimental evidence by measuring the performance metrics of an operational upconversion-based solar cell.56 Photocurrent was generated

Felix N. Castellano*

■

Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204, United States

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Felix N. Castellano: 0000-0001-7546-8618 Notes

Views expressed in this editorial are those of the author and not necessarily the views of the ACS.

■

REFERENCES

(1) Balzani, V.; Carassiti, V. Photochemistry of Coordination Compounds; Academic Press: New York, 1970. (2) Adamson, A. W.; Fleischauer, P. D. Concepts of Inorganic Photochemistry; Wiley-Interscience: New York, 1975. (3) Paris, J. P.; Brandt, W. W. Charge transfer luminescence of a ruthenium(II) chelate. J. Am. Chem. Soc. 1959, 81, 5001−5002. (4) Adamson, A. W.; Demas, J. N. New photosensitizer. Tris(2,2′bipyridine)ruthenium(II) chloride. J. Am. Chem. Soc. 1971, 93 (7), 1800−1801. (5) Gafney, H. D.; Adamson, A. W. Excited state Ru(bipyr)32+ as an electron-transfer reductant. J. Am. Chem. Soc. 1972, 94 (23), 8238− 8239. (6) Crosby, G. A.; Perkins, W. G.; Klassen, D. M. Luminescence from transition-metal complexes: tris(2,2′-bipyridine)- and tris(1,10phenanthroline)ruthenium(II). J. Chem. Phys. 1965, 43 (5), 1498− 1503. (7) Klassen, D. M.; Crosby, G. A. Spectroscopic studies of ruthenium(II) complexes. Assignment of the luminescence. J. Chem. Phys. 1968, 48 (4), 1853−8. (8) Demas, J. N.; Crosby, G. A. The multiplicity of the emitting state of ruthenium(II) complexes. J. Mol. Spectrosc. 1968, 26 (1), 72−77. (9) Bock, C. R.; Meyer, T. J.; Whitten, D. G. Electron transfer quenching of the luminescent excited state of tris(2,2′-bipyridine)ruthenium(II). Flash photolysis relaxation technique for measuring the rates of very rapid electron transfer reactions. J. Am. Chem. Soc. 1974, 96 (14), 4710−4712. (10) Wrighton, M.; Markham, J. Quenching of the luminescent state of tris(2,2′-bipyridine)ruthenium(II) by electronic energy transfer. J. Phys. Chem. 1973, 77 (26), 3042−3044. (11) Creutz, C.; Sutin, N. Reaction of tris(bipyridine)ruthenium(III) with hydroxide and its application in a solar energy storage system. Proc. Natl. Acad. Sci. U. S. A. 1975, 72 (8), 2858−2862. (12) King, K. A.; Spellane, P. J.; Watts, R. J. Excited-State Properties of a Triply Ortho-Metalated Iridium(III) Complex. J. Am. Chem. Soc. 1985, 107, 1431−1432. 12485

DOI: 10.1021/acs.inorgchem.6b02830 Inorg. Chem. 2016, 55, 12483−12487

Inorganic Chemistry

Editorial

Importance of the Terpyridine Rocking Motion. Inorg. Chem. 2015, 54 (23), 11259−11268. (31) Mukherjee, S.; Bowman, D. N.; Jakubikova, E. Cyclometalated Fe(II) Complexes as Sensitizers in Dye-Sensitized Solar Cells. Inorg. Chem. 2015, 54 (2), 560−569. (32) Bowman, D. N.; Bondarev, A.; Mukherjee, S.; Jakubikova, E. Tuning the Electronic Structure of Fe(II) Polypyridines via Donor Atom and Ligand Scaffold Modifications: A Computational Study. Inorg. Chem. 2015, 54 (17), 8786−8793. (33) Harlang, T. C. B.; Liu, Y.; Gordivska, O.; Fredin, L. A.; Ponseca, C. S., Jr; Huang, P.; Chábera, P.; Kjaer, K. S.; Mateos, H.; Uhlig, J.; Lomoth, R.; Wallenberg, R.; Styring, S.; Persson, P.; Sundström, V.; Wärnmark, K. Iron sensitizer converts light to electrons with 92% yield. Nat. Chem. 2015, 7 (11), 883−889. (34) Liu, L.; Duchanois, T.; Etienne, T.; Monari, A.; Beley, M.; Assfeld, X.; Haacke, S.; Gros, P. C. A new record excited state 3MLCT lifetime for metalorganic iron(ii) complexes. Phys. Chem. Chem. Phys. 2016, 18 (18), 12550−12556. (35) Allampally, N. K.; Daniliuc, C.-G.; Strassert, C. A.; De Cola, L. Tuning the Structural and Photophysical Properties of Cationic Pt(II) Complexes Bearing Neutral Bis(triazolyl)pyridine Ligands. Inorg. Chem. 2015, 54 (4), 1588−1596. (36) Taylor, W. V.; Soto, U. H.; Lynch, V. M.; Rose, M. J. AntimonySupported Cu4I4 Cuboid with Short Cu−Cu Bonds: Structural Premise for Near-Infrared Thermoluminescence. Inorg. Chem. 2016, 55 (7), 3206−3208. (37) Zhang, Y.; Zhang, L.; Deng, R.; Tian, J.; Zong, Y.; Jin, D.; Liu, X. Multicolor Barcoding in a Single Upconversion Crystal. J. Am. Chem. Soc. 2014, 136 (13), 4893−4896. (38) Maza, W. A.; Padilla, R.; Morris, A. J. Concentration Dependent Dimensionality of Resonance Energy Transfer in a Postsynthetically Doped Morphologically Homologous Analogue of UiO-67 MOF with a Ruthenium(II) Polypyridyl Complex. J. Am. Chem. Soc. 2015, 137 (25), 8161−8168. (39) Mandal, K.; Demas, J. N. Surfactant-Enhanced Singlet Energy Transfer from the Charge Transfer Excited State of Tris(2,2′bipyridine)ruthenium(II). Chem. Phys. Lett. 1981, 84, 410. (40) Mandal, K.; Pearson, T. D. L.; Demas, J. N. Singlet Energy Transfer from the Charge Transfer Excited State of Tris(2,2′bipyridine)ruthenium(II). J. Chem. Phys. 1980, 73, 2507. (41) Zhou, X.; Tyson, D. S.; Castellano, F. N. First generation lightharvesting dendrimers with a [Ru(bpy)3]2+ core and aryl ether ligands functionalized with Coumarin 450. Angew. Chem., Int. Ed. 2000, 39 (23), 4301−4305. (42) Tyson, D. S.; Gryczynski, I.; Castellano, F. N. Long-range resonance energy transfer to [Ru(bpy)3]2+. J. Phys. Chem. A 2000, 104 (13), 2919−2924. (43) Luman, C. R.; Castellano, F. N. Lengthening of fluorescence lifetimes in self-organized metal-organic assemblies. Photochem. Photobiol. 2003, 77 (5), 510−514. (44) Giammanco, G. E.; Ostrowski, A. D. Photopatterning the Mechanical Properties of Polysaccharide-Containing Gels Using Fe3+ coordination. Chem. Mater. 2015, 27 (14), 4922−4925. (45) Razgoniaev, A. O.; Butaeva, E. V.; Iretskii, A. V.; Ostrowski, A. D. Changing Mechanical Strength in Cr(III)- Metallosupramolecular Polymers with Ligand Groups and Light Irradiation. Inorg. Chem. 2016, 55 (11), 5430−5437. (46) Smith, R. D. L.; Sporinova, B.; Fagan, R. D.; Trudel, S.; Berlinguette, C. P. Facile Photochemical Preparation of Amorphous Iridium Oxide Films for Water Oxidation Catalysis. Chem. Mater. 2014, 26 (4), 1654−1659. (47) Kurzman, J. A.; Dettelbach, K. E.; Martinolich, A. J.; Berlinguette, C. P.; Neilson, J. R. Structural Characteristics and Eutaxy in the Photo-Deposited Amorphous Iron Oxide Oxygen Evolution Catalyst. Chem. Mater. 2015, 27 (9), 3462−3470. (48) Zandi, O.; Schon, A. R.; Hajibabaei, H.; Hamann, T. W. Enhanced Charge Separation and Collection in High-Performance Electrodeposited Hematite Films. Chem. Mater. 2016, 28 (3), 765− 771.

(13) Adachi, C.; Baldo, M. A.; Forrest, S. R.; Thompson, M. E. Highefficiency organic electrophosphorescent devices with tris(2phenylpyridine)iridium doped into electron-transporting materials. Appl. Phys. Lett. 2000, 77 (6), 904−906. (14) Yang, X.; Zhou, G.; Wong, W.-Y. Functionalization of phosphorescent emitters and their host materials by main-group elements for phosphorescent organic light-emitting devices. Chem. Soc. Rev. 2015, 44 (23), 8484−8575. (15) Radwan, Y. K.; Maity, A.; Teets, T. S. Manipulating the Excited States of Cyclometalated Iridium Complexes with β-Ketoiminate and β-Diketiminate Ligands. Inorg. Chem. 2015, 54 (14), 7122−7131. (16) Maity, A.; Le, L. Q.; Zhu, Z.; Bao, J.; Teets, T. S. Steric and Electronic Influence of Aryl Isocyanides on the Properties of Iridium(III) Cyclometalates. Inorg. Chem. 2016, 55 (5), 2299−2308. (17) de Bettencourt-Dias, A. Editorial for the Virtual Issue on Photochemistry and Photophysics of Lanthanide Compounds. Inorg. Chem. 2016, 55 (7), 3199−3202. (18) Agbo, P.; Abergel, R. J. Ligand-Sensitized Lanthanide Nanocrystals: Merging Solid-State Photophysics and Molecular Solution Chemistry. Inorg. Chem. 2016, 55 (20), 9973−9980. (19) Scattergood, P. A.; Khushnood, U.; Tariq, A.; Cooke, D. J.; Rice, C. R.; Elliott, P. I. P. Photochemistry of [Ru(pytz)(btz)2]2+ and Characterization of a κ1-btz Ligand-Loss Intermediate. Inorg. Chem. 2016, 55 (15), 7787−7796. (20) Barthelmes, K.; Kübel, J.; Winter, A.; Wächtler, M.; Friebe, C.; Dietzek, B.; Schubert, U. S. New Ruthenium Bis(terpyridine) Methanofullerene and Pyrrolidinofullerene Complexes: Synthesis and Electrochemical and Photophysical Properties. Inorg. Chem. 2015, 54 (7), 3159−3171. (21) Barthelmes, K.; Jäger, M.; Kübel, J.; Friebe, C.; Winter, A.; Wächtler, M.; Dietzek, B.; Schubert, U. S. Efficient Energy Transfer and Metal Coupling in Cyanide-Bridged Heterodinuclear Complexes B a s e d o n ( B i p y r i di n e ) ( t e r py r i d i n e ) r u t h en iu m ( I I ) a nd (Phenylpyridine)iridium(III) Complexes. Inorg. Chem. 2016, 55 (11), 5152−5167. (22) Robin, M. B.; Day, P. Mixed Valence ChemistryA Survey and Classification. In Advances in Inorganic Chemistry Radiochemistry; Emeléus, H. J., Sharpe, A. G., Eds.; Academic Press: New York, 1968; Vol. 10, pp 247−422. (23) Youinou, M.-T.; Ziessel, R. Synthesis and molecular structure of a new family of iridium-(III) and rhodium(III) complexes: [(η5Me5C5)Ir(LL)X]+ and [(η5-Me5C5)Rh(LL)Cl]+; LL = 2,2′-bipyridine or 1,10-phenanthroline; X = Cl or H. Single crystal structures of [(η5Me5C5)Ir(bpy)Cl]Cl and [(η5-Me5C5)Rh(phen)Cl]ClO4. J. Organomet. Chem. 1989, 363 (1), 197−208. (24) Suenobu, T.; Guldi, D. M.; Ogo, S.; Fukuzumi, S. Excited-State Deprotonation and H/D Exchange of an Iridium Hydride Complex. Angew. Chem., Int. Ed. 2003, 42 (44), 5492−5495. (25) Brewster, T. P.; Miller, A. J. M.; Heinekey, D. M.; Goldberg, K. I. Hydrogenation of Carboxylic Acids Catalyzed by Half-Sandwich Complexes of Iridium and Rhodium. J. Am. Chem. Soc. 2013, 135 (43), 16022−16025. (26) Pitman, C. L.; Miller, A. J. M. Molecular Photoelectrocatalysts for Visible Light-Driven Hydrogen Evolution from Neutral Water. ACS Catal. 2014, 4 (8), 2727−2733. (27) Barrett, S. M.; Slattery, S. A.; Miller, A. J. M. Photochemical Formic Acid Dehydrogenation by Iridium Complexes: Understanding Mechanism and Overcoming Deactivation. ACS Catal. 2015, 5 (11), 6320−6327. (28) Chambers, M. B.; Kurtz, D. A.; Pitman, C. L.; Brennaman, M. K.; Miller, A. J. M. Efficient Photochemical Dihydrogen Generation Initiated by a Bimetallic Self-Quenching Mechanism. J. Am. Chem. Soc. 2016, 138 (41), 13509−13512. (29) Su, X.; Hu, R.; Li, X.; Zhu, J.; Luo, F.; Niu, X.; Li, M.; Zhao, Q. Hydrophilic Indolium Cycloruthenated Complex System for Visual Detection of Bisulfite with a Large Red Shift in Absorption. Inorg. Chem. 2016, 55 (2), 745−754. (30) Nance, J.; Bowman, D. N.; Mukherjee, S.; Kelley, C. T.; Jakubikova, E. Insights into the Spin-State Transitions in [Fe(tpy)2]2+: 12486

DOI: 10.1021/acs.inorgchem.6b02830 Inorg. Chem. 2016, 55, 12483−12487

Inorganic Chemistry

Editorial

(49) Kanan, M. W.; Nocera, D. G. In Situ Formation of an OxygenEvolving Catalyst in Neutral Water Containing Phosphate and Co2+. Science 2008, 321 (5892), 1072−1075. (50) Wilker, M. B.; Shinopoulos, K. E.; Brown, K. A.; Mulder, D. W.; King, P. W.; Dukovic, G. Electron Transfer Kinetics in CdS Nanorod− [FeFe]-Hydrogenase Complexes and Implications for Photochemical H2 Generation. J. Am. Chem. Soc. 2014, 136 (11), 4316−4324. (51) Chuang, C.-H.; Lu, Y.-G.; Lee, K.; Ciston, J.; Dukovic, G. Strong Visible Absorption and Broad Time Scale Excited-State Relaxation in (Ga1−xZnx)(N1−xOx) Nanocrystals. J. Am. Chem. Soc. 2015, 137 (20), 6452−6455. (52) Mongin, C.; Garakyaraghi, S.; Razgoniaeva, N.; Zamkov, M.; Castellano, F. N. Direct observation of triplet energy transfer from semiconductor nanocrystals. Science 2016, 351 (6271), 369−372. (53) Singh-Rachford, T. N.; Castellano, F. N. Photon Upconversion Based on Sensitized Triplet-Triplet Annihilation. Coord. Chem. Rev. 2010, 254, 2560−2573. (54) Schmidt, T. W.; Castellano, F. N. Photochemical Upconversion: The Primacy of Kinetics. J. Phys. Chem. Lett. 2014, 5 (22), 4062−4072. (55) Hill, S. P.; Banerjee, T.; Dilbeck, T.; Hanson, K. Photon Upconversion and Photocurrent Generation via Self-Assembly at Organic−Inorganic Interfaces. J. Phys. Chem. Lett. 2015, 6 (22), 4510− 4517. (56) Hill, S. P.; Dilbeck, T.; Baduell, E.; Hanson, K. Integrated Photon Upconversion Solar Cell via Molecular Self-Assembled Bilayers. ACS Energy Lett. 2016, 1 (1), 3−8. (57) Haefele, A.; Blumhoff, J.; Khnayzer, R. S.; Castellano, F. N. Getting to the (Square) Root of the Problem: How to Make Noncoherent Pumped Upconversion Linear. J. Phys. Chem. Lett. 2012, 3, 299−303.

12487

DOI: 10.1021/acs.inorgchem.6b02830 Inorg. Chem. 2016, 55, 12483−12487