Inorganic Photochemistry

446 Pages·2011·14.57 MB·English

by  Rudi van Eldik and Grażyna Stochel (Eds.)

ADVISORY BOARD
I. Bertini D. Darensbourg
UniversitadegliStudidiFirenze TexasA&MUniversity
Florence,Italy CollegeStation,Texas,USA
L. H. Gade H. B. Gray
UniversitätHeidelberg CaliforniaInstituteofTechnology
Germany Pasadena,California,USA
M. L. H. Green P. A. Lay
UniversityofOxford UniversityofSydney
Oxford,UnitedKingdom Sydney,Australia
A. E. Merbach J. Reedijk
LaboratoiredeChimieetBioanorganique LeidenUniversity
EFPL,Lausanne,Switzerland Leiden,TheNetherlands
P. J. Sadler Y. Sasaki
UniversityofWarwick HokkaidoUniversity
Warwick,England Sapporo,Japan
K. Wieghardt
Max-Planck-Institut
Mülheim,Germany
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LIST OF CONTRIBUTORS
Luis G. Arnaut ResearchSeedsProgram,JapanScience
ChemistryDepartment,Universityof andTechnologyAgency(JST),Kawaguchi,
Coimbra,Coimbra,Portugal Saitama,Japan
Vincenzo Balzani James P. Kirby
DipartimentodiChimica“G.Ciamician”, PlanetaryScienceSection,JetPropulsion
UniversitàdiBologna,viaSelmi2, Laboratory,Pasadena,California,USA
Bologna,Italy
Horst Kisch
Giacomo Bergamini DepartmentofChemistryand
DipartimentodiChimica“G.Ciamician”, Pharmacy,InstituteofInorganicChemistry,
UniversitàdiBologna,viaSelmi2,Bologna, Friedrich-Alexander-UniversitätErlangen-
Italy Nürnbegrg,Egerlandstraße1,Erlangen,
Germany
Morgan L. Cable
Günther Knör
PlanetaryScienceSection,JetPropulsion
Laboratory,andBeckmanInstitute, InstituteofInorganicChemistry,Johannes
CaliforniaInstituteofTechnology, KeplerUniversity(JKU),Linz,Austria
Pasadena,California,USA
Kazuhide Koike
Paola Ceroni CoreResearchforEvolutionalScienceand
DipartimentodiChimica“G.Ciamician”, Technology(CREST),JapanScienceand
UniversitàdiBologna,viaSelmi2,Bologna, TechnologyAgency(JST),Kawaguchi,
Italy Saitama,andNationalInstituteofAdvanced
IndustrialScienceandTechnology,
Tsukuba,Ibaraki,Japan
Luisa De Cola
PhysikalischesInstitut,Westfälische
Horst Kunkely
WilhemsUniversitätMünster,
Mendesltrasse7,andCenterfor InstitutfürAnorganischeChemie,
Nanotechnology,CeNTech, UniversitätRegensburg,93040
Heisenbergstrasse11,Münster,Germany Regensburg,Germany
Harry B. Gray Dana J. Levine
BeckmanInstitute,CaliforniaInstituteof BeckmanInstitute,CaliforniaInstitute
Technology,Pasadena,California,USA ofTechnology,Pasadena,California,USA
Hiroki Inumaru Matteo Mauro
DepartmentofChemistry,TokyoInstituteof PhysikalischesInstitut,Westfälische
Technology,Tokyo,Japan WilhemsUniversitätMünster,
Mendesltrasse7,andCenterfor
Nanotechnology,CeNTech,
Osamu Ishitani
Heisenbergstrasse11,Münster,Germany
CoreResearchforEvolutionalScienceand
Technology(CREST),JapanScienceand
Uwe Monkowius
TechnologyAgency(JST),Kawaguchi,
Saitama,DepartmentofChemistry,Tokyo InstituteofInorganicChemistry,Johannes
InstituteofTechnology,Tokyo,and KeplerUniversity(JKU),Linz,Austria
ix
x LISTOFCONTRIBUTORS
Tatsuki Morimoto Mendesltrasse7,andCenter
DepartmentofChemistry,TokyoInstituteof forNanotechnology,CeNTech,
Technology,Tokyo,Japan Heisenbergstrasse11,Münster,Germany
B. Ohtani Hiroyuki Takeda
CatalysisResearchCenter,Hokkaido ToyotaCentralR&DLaboratories,Inc.,
University,Sapporo,Japan Nagakute,Aichi,andCoreResearchfor
EvolutionalScienceandTechnology
(CREST),JapanScienceandTechnology
Adrian Ponce
Agency(JST),Kawaguchi,Saitama,Japan
PlanetaryScienceSection,JetPropulsion
Laboratory,Pasadena,California,USA
Arnd Vogler
InstitutfürAnorganischeChemie,Universität
Zofia Stasicka
Regensburg,93040Regensburg,Germany
FacultyofChemistry,Jagiellonian
University,Ingardena3,Kraków,Poland
Cristian A. Strassert
PhysikalischesInstitut,Westfälische
WilhemsUniversitätMünster,
PREFACE
Volume 63 of Advances in Inorganic Chemistry is a thematic
issue devoted to inorganic photochemistry, coedited by Graz˙yna
Stochel from the Jagiellonian University in Kraków, Poland.
Photochemistry has always played an important role in inor-
ganic/bioinorganic chemistry, and with the development of
sophisticated instrumentation, the underlying physical and
chemical processes have been clarified to a significant degree in
recent years. Inorganic photochemistry presently finds applica-
tion in diverse areas such as sensor technology, molecular
assemblies, catalysis, medical therapy, biomimetics, activation
of small molecules,semiconductors,solid materials,and environ-
mental processes. This volume includes 10 contributions
highlighting the role of photochemistry in a broad spectrum of
inorganic chemistry. We hope it will prove interesting and
inspiring to researchers in this field.
ThefirstchapterbyHarryB.Grayandcollaboratorspresentsa
detailed account on luminescent lanthanide sensors. This is
followedbyachapteronthephoto-physicsofsoftandhardmolec-
ularassembliesbasedinluminescentcomplexeswrittenbyLuisa
deColaandcollaborators.Thephotochemistryandphoto-physics
of metal complexes with dendritic ligands are covered in the fol-
lowing chapter by Vincenzo Balzani and collaborators. In the
fourth chapter, Osamu Ishitani and collaborators present an
account on the photochemistry and photo-catalysis of rhenium(I)
diimine complexes. In the subsequent chapter, Luis G. Arnaut
reports on the design of porphyrin-based photosensitizers for
photodynamic therapy. Photosensitization and photo-catalysis in
bioinorganic, bio-organometallic, and biomimetic systems are
covered by Günther Knör and collaborator in the sixth chapter.
A short review on recent developments in transition metal
complexes as solar photo-catalysts in the environment is pres-
ented in the seventh chapter by Zofia Stasicka. This is followed
byacontributionfromArndVoglerandcollaboratoronthephoto-
chemicalactivationandsplittingofwater,CO ,andN inducedby
2 2
chargetransferexcitationofredox-activemetalcomplexes.Inthe
ninthchapter,HorstKischreportsonvisiblelightphoto-catalysis
by metal halide complexes containing titania as a semiconductor
xi
xii PREFACE
ligand,andinthefinalchapter,BunshoOhtanipresentsacontri-
butiononphoto-catalysisbyinorganicsolidmaterials,inwhichhe
revisitsthedefinition,concepts,andexperimentalprocedures.
We appreciate the constructive interaction we had with the
authors of these chapters and thank them for their willingness
to find time to contribute to this thematic issue. We trust that
the readers in the inorganic/bioinorganic chemistry communities
will find this volume informative and useful.
Rudi van Eldik
University of Erlangen-Nürnberg
Germany
Graz˙yna Stochel
Jagiellonian University
Poland
May 2011
LUMINESCENT LANTHANIDE SENSORS
MORGAN L. CABLEa,b, DANA J. LEVINEb,1, JAMES P. KIRBYa,
HARRY B. GRAYb and ADRIAN PONCEa
aPlanetaryScienceSection,JetPropulsionLaboratory,Pasadena,California,USA
bBeckmanInstitute,CaliforniaInstituteofTechnology,Pasadena,California,USA
I. Introduction 2
A. Lanthanides 2
B. LanthanideSensitization 5
C. LanthanideReceptors 9
II. Effectsof AncillaryLigands 10
A. Photophysics 10
B. Stability 15
C. Sensitivity 21
D. Selectivity 27
III. AdditionalFactorsThatGovernComplexStability 30
A. StericEffects 30
B. Oxophilicity 31
IV. LookingtotheFuture 35
V. Conclusions 38
Abbreviations 39
Acknowledgments 40
References 40
ABSTRACT
Luminescent lanthanide optical sensors have been developed
that utilize ancillary ligands to enhance detection of a target
analyte. In these systems, the lanthanide (ligand) binary com-
plex serves as the receptor, which upon analyte binding forms a
ternary complex resulting in detectable change in lanthanide
luminescence (Fig. 1). The ancillary ligand improves many pro-
perties of analyte detection by protecting the lanthanide and
strengthening analyte binding affinity. Encapsulation shields
1Current address: Department of Chemistry, University of California,
Berkeley,California,USA
1
INORGANICPHOTOCHEMISTRY #2011ElsevierInc.
VOLUME63ISSN0898-8838/DOI:10.1016/B978-0-12-385904-4.00010-X Allrightsreserved
2 MORGANL.CABLEetal.
thelanthanideionfromsolvent-quenchingeffectsandinterfering
ions, improving assay sensitivity and selectivity. The ligand-
induced enhancementin binding affinity appearsto bethe result
of an increase in positive charge at the analyte binding site due
to the electronegative ancillary ligand bound on the opposite
hemisphere of the lanthanide. We have elucidated the effects of
ancillary ligands for various lanthanide/analyte systems and
shown how such effects can greatly improve sensor performance
for medical, planetary science, and biodefense applications.
Keywords: Lanthanide; Sensor; Sensitized luminescence;
Dipicolinate; Macrocycle; Ternary complex; Bacterial spore;
Ancillary ligand; Gadolinium break; Catecholamine; Salicylic
acid; Salicylurate.
I. Introduction
A. LANTHANIDES
The lanthanides, or lanthanoids, are elements with lives of
their own—enigmatic, difficult to separate and purify— and
most often pictured as a row orphaned from the rest of
the periodic table along with their more radioactive siblings,
the actinides. Also known as “rare earth elements” due to the
etymology of the term “lanthanide” (derived from the Greek
lanthanein, meaning “to lie hidden”), they include the 15
elements of the top row in the “f-block” and have electronic
configurations [Xe] 4fn5s25p6, where n varies from 0 to 14. Inter-
estingly, lanthanides are neither rare nor “earths,” an old term
used to describe certain metal oxides such as lime and magnesia
(1). Even the rarest lanthanides—thullium and lutetium—are
two orders of magnitude more abundant than gold (2).
Lanthanideshavefoundusesascatalysts,ceramics,andperma-
nent magnets, as well as in optics and electronics (3,4). S olid
phosphorscontainingeuropium,cerium,andterbiumarefoundin
many common fluorescent lighting and color displays. Various
lanthanide ions are used in lasers, with neodymium as the
most famous in yttrium aluminum garnet (Nd-YAG). The green,
blue, and red luminescent bands in Euro banknotes are from
europium complexes (5). Certain lanthanides are used as tracers
in winechemistry todiscriminatewinesaccordingtogeographical
region (6). The ratio of europium, which is almost entirely formed
in stars, to other rare earth elements in meteorites has helped
LUMINESCENT LANTHANIDESENSORS 3
us decipher much of the history of processes in our solar system,
includingtheearlydevelopmentofthefeldspar-richlunarcrust(7).
In aqueous solution, lanthanides are most stable in the
tripositive oxidation state, making them difficult to separate
and purify. The preference for this oxidation state is due in part
to the energy of the 4f electrons being below those of the 5d and
6s electrons (except in the cases of La and Ce). When forming
ions, electrons from the 6s and 5d orbitals are lost first so that
all Ln3þ ions have [Xe] 4fn electronic configurations. Under
reducing conditions, certain lanthanides (europium, samarium,
and ytterbium) can be stable as dipositive ions, and cerium can
adopt a þ4 oxidation state (5).
Lanthanide ions are hard Lewis acids: the 4f orbitals are well
shielded by the 5s and 6p orbitals and do not participate directly
in bonding, p-bonding is disfavored, and there are no complexes
with Ln(cid:2)(cid:2)O or Ln(cid:2)(cid:2)N multiple bonds. Coordination to Ln3þ is
ionic in character, leading to a strong preference for negatively
charged or neutral donor groups with large ground state dipole
moments (Fig. 1). Combinations of amines and carboxylic acid
groups are therefore often used for lanthanide complexation
(8,9). Coordination geometries in lanthanides are determined by
ligand steric factors as opposed to orbital overlap or crystal field
effects (10,11). In aqueous solution, donor groups containing
neutraloxygenornitrogenatomsgenerallybindwhenpresentin
multidentate ligands, such as podands, crown ethers, and cryp-
tates (12–15). Relatively few complexes of monodentate nitrogen
donorsareknown,suggestinganoxophilictendencyoflanthanide
binding.Thispreferenceforoxygendonorsalsomakeslanthanides
quite lithophilic and explains their occurrence in silicates as
opposedtometallicorsulfidicminerals(16).
FIG. 1. Binding of an analyte to a lanthanide-based receptor pro-
ducesaluminescentternarycomplex.Theancillary(receptororhelper)
ligand is shown in dark gray.
4 MORGANL.CABLEetal.
The coordination number of [Ln(H O) ]3þ is normally 9 for the
2 n
early lanthanides (La–Eu) and 8 for those later in the series
(Dy–Lu), with the intermediate metals (Sm–Dy) exhibiting a
mixture of species. However, the coordination number can be
dictated by the steric bulk of the coordinating ligands, and
species with coordination numbers as low as 2 and as high as
12 are known (5,17).
With the 4f electrons well shielded from the environment,
the spectroscopic and magnetic properties of the lanthanides
(e.g., electronic spectra and crystal field splittings) are largely
independent of environmental factors (solvent, coordinated
ligands). The number of electronic configurations is a function of
thenumberofunpairedelectronswhere0(cid:3)x(cid:3)14,withthelowest
energytermforeachionconsistentwiththepredictionsofHund's
firstandsecondrules(18,19).Owinginparttospin–orbitcoupling,
thelanthanidesexhibitarichenergylevelpattern,withthelowest
electronicexcitedstatessignificantlyabovethegroundstate(20).
Asf–ftransitionsareelectricdipoleforbidden(butmagneticdipole
allowed), lanthanide ion absorptions are very weak
(E(cid:4)0.1mol–1dm3cm–1) (5,21–23). Electronic transitions must
involve promotion of an electron without a change in its spin
(DS¼0) and with a variation of either total angular momentum
ortotalangularquantumnumberofoneunitatmost(DL¼(cid:5)1.0;
DJ¼(cid:5)1.0).Thoughabsorptionofradiationcanintheorypromote
the lanthanide ion to any energetically accessible state, emission
normallyoccursonlyfromthelowestlyingenergylevelofthefirst
excitedtermduetorapidinternalconversion(IC)(19).Incasesof
low symmetry or vibronic coupling, the f–f transitions can gain
intensity through f- and d-state mixing with higher electronic
states of opposite parity. Broad 4fn!4fn–1 5d1 transitions also
canbeseenintheinfraredregionforsomelanthanides.
TheelectronicconfigurationsofLn3þionsaresplitbyelectronic
repulsion, with term separations on the order of 104cm–1 (Fig. 2)
(24). These terms are split further by spin–orbit coupling into J
states, with energy differences in the 103cm–1 range (25). These
spectroscopic levels can be split once again into what are termed
Stark sublevels due to ligand-field effects from the coordination
sphere around the lanthanide; Stark sublevel splitting is on the
order of 102cm–1 (26). The emission peak positions in Ln3þ
complexes do not vary substantially, because the f-electrons are
shielded,butanemissionprofile(definedastherelativeintensity
and degree of splitting of an emission band) can vary greatly
(21,27).ThenumberofStarksublevelsdependsonthesitesymme-
tryofthelanthanideion,andthesecanbethermallypopulatedat
roomtemperature,yieldingmorecomplexemissionspectra.