Download transition metal complexes possessing tunable and switchable

1
GRANT GR/M93864/01: REVIEW REPORT
‘TRANSITION METAL COMPLEXES POSSESSING TUNABLE AND SWITCHABLE
NONLINEAR OPTICAL PROPERTIES’
BACKGROUND/CONTEXT
Because optoelectronic or all-optical (photonic) data processing offer immense benefits over current
microelectronics technologies in terms of speed and scale of operation, extensive research has been carried out in
recent years on materials with nonlinear optical (NLO) properties. Organic molecular materials are especially
promising in this area because they may be readily processed for incorporation into optical devices, e.g.
waveguides, and their often very large NLO responses can be tuned via synthetic chemistry.1 As an interesting
sub-class of molecular NLO materials, organotransition metal complexes offer extensive possibilities for
combining a range of optical effects with other molecular electronic properties (e.g. redox or magnetic behaviour).2
More recent research involving such compounds has generally focused on the establishment of molecular structureactivity relationships, which are currently considerably better developed for purely organic NLO chromophores.
Quadratic (second-order) NLO properties derive at the molecular level from first hyperpolarizability
coefficients β, which translate into bulk susceptibilities χ(2) in appropriate macroscopic structures. Most known
molecules with large β responses contain a powerful electron donor (D) group and an electron acceptor (A)
connected via a conjugated π-bridge. Such D-π-A dipolar chromophores also show intense, low-energy absorption
bands due to D(π)→A(π*) intramolecular charge-transfer (ICT) transitions. Therefore, ICT resonances can have
pronounced enhancing effects on experimentally measured β values, and it is necessary to derive static first
hyperpolarizabilities β0, which can be estimated by application of a widely used two-state model (TSM) for dipolar
chromophores.3 β0 values are a measure of the intrinsic quadratic NLO response under non-resonant (i.e. working)
conditions, and are of particular relevance to device applications where any actual absorption of light must be
avoided.
NH3
H 3N
Me2N
Ru
N
O
+
N
N
3+ [PF6– ]3
NH3
H 3N
N
Ru
N
Me
H 3N
H 3N
NH3
1 (λmax[MLCT] = 688 nm; β0[HRS] = 410 × 10–30 esu)6c
NH3
H 3N
H 3N
H 3N
Ru
N
+
N
Me2N
NH3
3 (λmax[MLC T] = 628 nm; β0[HRS] = 220 ×
β0[Stark] = 93 × 10–30 esu)10
NH3
2 (λmax[MLCT] = 591 nm; β0[HRS] = 151 × 10–30 esu)6d
3+ [PF6– ]3
10–30
3+ [PF6– ]3
+
N
esu;6c
+
N
PF6–
4 (λmax[ICT] = 448 nm; β0[HRS] = 45 × 10–30 esu;10
β0[Stark] = 75 × 10–30 esu)10
By exploiting a combination of hyper-Rayleigh scattering (HRS) measurements4 and electronic Stark effect
(electroabsorption) spectroscopy,5 we have discovered that ruthenium pyridyl ammine complex salts containing
pyridinium A groups (e.g. 1 and 2) can have very large β0 values which are associated with intense, low energy
metal-to-ligand charge-transfer (MLCT) excitations.6 For comparison, the benchmark dipolar organic
chromophore 4-dimethylamino-4′-nitrostilbene has a β0 value of 55 × 10–30 esu.7 Both the MLCT absorption and
NLO properties of our complexes are readily tunable by ligand-based changes, in general accordance with the
TSM, and can also be reversibly switched by using the RuIII/II redox couple. 8 The latter observation was a world
first which has been followed by similar reports by several reknowned international groups in the NLO field.9 In
addition, the first detailed and quantitative comparisons involving metal complexes and related purely organic
chromophores have led to the conclusion that a pyridyl-coordinated {RuII (NH 3 ) 5 }2+ centre is a more effective πelectron donor than the widely used -NMe2 group.10 This result can be traced to the fact that the higher HOMO
energy of the RuII centre more than offsets the stronger π-orbital overlap in analogous organic chromophores (e.g.
compare 3 and 4).10
2
KEY ADVANCES AND SUPPORTING METHODOLOGY
Synthetic and Characterization Studies (mapped on to original proposal)
(i) Mixed-valent Complexes
Inspired by previous studies which showed that cyanide-bridged, mixed-valent ruthenium complexes can
exhibit large NLO responses,11 we sought to prepare dinuclear complex salts such as 5. In such species it was
envisaged that the electron-rich pentaammine centres (E1/2[RuIII/II ] ≈ 0.4 V vs. SCE) should be readily and
selectively oxidized to afford mixed-valent complexes in which both MLCT and RuII →RuIII inter-valence chargetransfer excitations should combine to produce very large β0 values. Although we have successfully prepared and
partially characterized 5 and also the related pyrazine and 4,4′-bipyridine containing species, these compounds
have proven to be inexplicably unstable. After repeated attempts to isolate sufficient samples for further oxidation,
this work was discontinued in favour of other more promising avenues of investigation.
(ii) Complexes of Pyridyl Polyene Ligands
For strategic reasons, these synthetic studies were actually carried out by another PDRA supported by
different EPSRC grants (Dr Lathe A Jones; grant refs GR/L56213/01 and GR/R54293/01). A number of
complexes containing RuII ammine centres connected to pyridinium A groups via extended polyenyl bridges were
prepared and fully characterized, and have been described in the previous IGRs. However, the important Stark
spectroscopic studies on these compounds were funded by the present grant and carried out by Dr Harris (see
later).
[PF6– ]9
Ru(NH3)5 9+
N
AsMe2
Me2As
Cl
Ru
H 3N
4+ [PF6– ]4
N
N
Me2As
NH3
Ru
AsMe2
H 3N
6
N+
NH3
N
NH3
+
N
5
(NH3)5Ru
N
N
N
+
N
N
Ru(NH3)5
(iii) Octopolar Complexes
Octopolar compounds are an important class of quadratic NLO materials,12 and we therefore planned to
prepare and study D3h complex salts such as 6 in which three powerful RuII ammine donors are connected via a
central electron-deficient 2,4,6-triazenyl core. The proposed synthetic approach, in which mononuclear complexes
of ligands such as 4,4′-bipyridine are reacted with cyanuric chloride, proved to be successful. However, the
products were found to be unstable and steadily decomposed on attempts at purification. We have not been able to
identify the cause of this unfortunate instability, but suspect that it may arise from the extreme electron-deficiency
of the central units. Although 1,3,5-triaryl-2,4,6-triazenyl derivatives have been isolated previously,12b systems
with three pyridinium rings attached are not known. We have carried out some preliminary experiments working
towards species related to 6 with central benzene rings, but limited progress was possible under the present grant.
A number of previous NLO studies have been carried out with derivatives of RuII tris(2,2′-bipyridine) (and
related complexes of other metals), 13 which although often described as octopolar,13a,b,d-f may more realistically be
viewed as a multi-dipolar chromophores.13c However, all of these studies have involved ligands bearing electrondonating groups, and the MLCT transitions in such compounds are necessarily opposed to the intraligand chargetransfer (ILCT) excitations which dominate the β responses. We therefore decided that it would be interesting to
prepare related chromophores in which the ligands are subsituted with electron-withdrawing pyridinium groups.
Such species can be expected to have more truly octopolar electronic structures in which only MLCT transitions
determine the NLO properties.
We have prepared the new dications N′′,N′′′-di-R-2,2′:4,4′′:4′,4′′′-quaterpyridinium (R = phenyl, Ph2 Qpy2+;
2,4-dinitrophenyl, (2,4-DNPh)2 Qpy2+; 4-acetylphenyl, (4-AcPh) 2 Qpy2+; 3,5-bis-methoxycarbonylphenyl, (3,5MCPh)2Qpy2+) (Scheme 1) and isolated them as their PF6 – salts. These compounds and the known pro-ligand salt
[Me2Qpy2+][PF6] 2 14 have been used to prepare a series of seven new complex salts [MII(R2 Qpy2+)3 ][PF 6 ] 8 (M = Ru,
R = Me 7, Ph 8, 4-AcPh 9, 3,5-MCPh 10; M = Fe, R = Me 11, Ph 12, 4-AcPh 13). 7–13 have been fully
3
characterized by using the usual techniques including cyclic voltammetry and UV-visible absorption spectroscopy.
The absorption spectra of these compounds display intense, visible MLCT bands, the energies (Emax) of which
decrease in the order R = Me > Ph > 4-AcPh = 3,5-MCPh, as the electron-accepting ability of the pyridinium
groups increases. Each of the RuII complexes in 7–10 shows two overlapping MLCT bands, whilst the FeII
complexes in 11–13 display two well-separated bands. The cyclic voltammograms show quasi-reversible MIII/II
waves which are found at lower potentials for the FeII complexes when compared with their RuII analogues, due to
the greater electron-richness of the FeII centres.
10 eq
N
N
NO2
O2N
O2 N
O2N
NO2
NO2
Cl
N
2+
N
Scheme 1
+
N
+
N
EtOH ∆ 48 h
(2,4-DNPh)2Qpy2+
O
N
N
OMe
11 eq
EtOH ∆ 50 h
10 eq H2N
O
H 2N
OMe
Me
O
OMe
MeO
O
O
OMe
MeO
O
+
N
+
N
N
O
EtOH ∆ 50 h
DMSO 70 °C 3 h
11 eq H2N
Me
Me
O
O
2+
2+
2+
+
N
+
N
+
N
N
N
(3,5-MCPh)2Qpy2+
+
N
N
N
Ph2Qpy2+
N
(4-AcPh)2Qpy2+
(iv) Complex Salts for Redox-switchable NLO-active Thin Films
Macroscopic quadratic NLO activity requires non-centrosymmetric bulk structures,1 and these can be created
on various substrates by using the Langmuir-Blodgett (LB) film deposition technique.15 Several reports of RuII
complexes in LB films with NLO activity have already appeared. 16 We have synthesized several new dipolar
complex salts designed to possess the amphiphilic properties necessary for LB film formation. The pro-ligands
14–16 were prepared by adapting existing chemistry6c and used to synthesize their {RuII (NH3)}2+ complexes
which were isolated and fully characterised as both their PF6– and n-dodecylsulfate salts. LB-deposition requires
compounds that are completely insoluble in water, but soluble in water-immiscible organic solvents (e.g.
chloroform, hexane, toluene, etc.). Unfortunately, the salts which we have prepared show considerable water
solubility and only limited solubility in non-polar organic solvents. We have attempted to circumvent this problem
by using other counterions such as BPh4 – , but have not succeeded in isolating any water-insoluble materials. It
appears that the ammine ligands are especially good at engendering aqueous solubility, and our conclusion is that
they will have to be replaced by more hydrophobic ligands if salts with the necessary solubility properties are to be
prepared. Unfortunately, such a broadening of scope was considered to be beyond the present project, but it is
intended to pursue studies along these lines in the future now that the pro-ligands 14–16 are available.
O
OC6H13-n
+
N C6H13-n
N
14
N
+
N
15
C6H13-n
N
+
N
16
OC6H13-n
O
(v) V-Shaped Complexes (New Targets)
A variety of organic multidimensional NLO compounds have recently emerged as candidates for quadratic
applications,12,17 offering potential advantages over 1D chromophores such as increased β responses without
undesirable losses of transparency in the visible region. Dipolar 2D C 2 v molecules, such as
(dicyanomethylene)pyran derivatives17a,e or asymmetrically substituted 1,3,5-tris(phenylethynyl)benzenes,17b,d with
4
large off-diagonal β components are attractive for electro-optic applications and also offer new possibilities for
achieving phase-matched seond harmonic generation. A relatively small number of neutral dipolar 2D metal
complexes have also been studied,2k,18 in particular Schiff base derivatives. We therefore sought to prepare and
study complexes relate to our existing 1D dipolar systems, but with V-shaped 2D structures based on cis
coordination geometries, together with some related trans complexes for comparison purposes.
+
N
NH3
H 3N
–
R 4+ [PF6 ]4
NH3
H 3N
N
Ru
H 3N
N
N
R
(20)
(19),
Me
(4-AcPh)
N
+
R
N
O
R = Me (17), Ph (18),
N
NH3
+
–
R 4+ [PF6 ]4
Ru
H 3N
N
NH3
+
N
R = Me (28), Ph (29), 4-AcPh (30), 2-Pym (31)
N
(2-Pym)
The existing pro-ligand salts N-R-4,4′-bipyridinium hexafluorophosphate (R = Me, MeQ +; Ph, PhQ +; 4acetylphenyl, 4-AcPhQ+; 2-pyrimidyl, 2-PymQ+ ) were used to prepare eleven new complex salts c i s [RuII (NH 3 ) 4 L2 ][PF6] 4 (L = MeQ + 17, PhQ + 18, 4-AcPhQ+ 19, 2-PymQ+ 20), trans-[RuII (NH 3 ) 4 L2 ][PF6] 4 (L = MeQ +
21, PhQ + 22, 4-AcPhQ+ 23, 2-PymQ + 24) and trans-[RuII (NH 3 ) 4 (MeQ +)L][PF6 ] 4 (L = PhQ + 25, 4-AcPhQ+ 26, 2PymQ+ 27). In addition, the new dicationic pro-ligand salt [(2-Pym)2 Qpy2+][PF 6 ] 2 and the related [R2 Qpy2+][PF6 ] 2
(R = Me, Ph, 4-AcPh) (see (iii) above) were used to synthesize four new complex salts c i s [RuII (NH 3 ) 4 (R2 Qpy2+)][PF6] 4 (R = Me 28, Ph 29, 4-AcPh 30, 2-Pym 31). The electronic absorption spectra of
17–31 display intense, visible MLCT bands, the energies of which decrease in the order R = Me > Ph > 4-AcPh >
2-Pym, as the electron-accepting ability of the pyridinium groups increases. Each of 17–20 shows two overlapping
MLCT bands, whilst 21–24 display single bands and 25–31 also show apparently single bands which are composed
of multiple transitions. Cyclic voltammetric studies show that the Ru-based HOMO energy is only slightly
sensitive to changes in the structure of the pyridinium ligands, but the LUMO energies exhibit a large variation.
The trends in the first ligand reduction potentials correlate with the Emax values. Furthermore, the extent of
electronic coupling between these ligands increases as reduction proceeds, and is also greater in the Qpy-based
complexes in 28 and 29 than in their non-chelated analogues in 17 and 18. A single crystal X-ray structure for the
pro-ligand salt [Ph2Qpy2+][PF6] 2 •Me 2 CO shows that the 2,2′-bipyridine unit adopts a planar, transoid geometry
with large dihedral angles between the two 4-pyridyl rings and between the pyridyl and attached phenyl rings.
Hyper-Rayleigh Scattering and Stark Spectroscopic Studies
The octopolar complexes described in (iii) above have been studied by HRS measurements, but so far only
with a 1300 nm laser fundamental. Unfortunately, the harmonic signals at 650 nm were too weak to allow β
determinations, but it is hoped that data will soon become available using a 800 nm laser. Stark spectroscopic
studies with 7−13 in butyronitrile glasses at 77 K, incorporating a Gaussian fitting approach, have afforded dipole
moment changes ∆µ12 for the MLCT transitions. These data have been used to calculate β0 values according to the
two-state equation β0 = 3∆µ12(µ12)2 /(Emax)2 (µ12 = transition dipole moment). In each case, the use of two dominant
Gaussian curves affords two components of the β response. For 7–10, Stark signals associated with the triplet
excited states are observed to the low energy side of the lowest energy absorption bands. The β0 values indicate
that the molecular quadratic NLO responses of 7–13 are highly 2D in nature, and some evidence for enhancement
of β0 on changing R from a Me to an aryl substituent is found.
The β values of the V-shaped complexes in 17–20 and 28–31 described in (v) above have been measured by
using the HRS technique with acetone or acetonitrile solutions and a 800 nm laser. Stark spectroscopic studies
with 17–20 and 28–31 in butyronitrile at 77 K, again using Gaussian fitting, have yielded ∆µ12 and therefore β0
values. In the cases of 17–20 and 28, the use of two dominant Gaussian curves affords two orthogonal components
of the β responses which lie in the range ca 40–160 × 10–30 esu. The HRS β800 values do not reveal any clear
trends within the two series, but the values for 28–31 are substantially smaller than those of their non-chelated
counterparts 17–20. As for 7–13, the β0 responses of 17–20 and 28 are strongly 2D, and these NLO responses also
appear to be greater in the N-arylated compounds, in keeping with the behaviour of related 1D dipolar systems.6b–e
This grant has also been used to fund Stark spectroscopic studies on a number of other complex salts which
were synthesized under closely related EPSRC grants (GR/L56213/01 and GR/R54293/01) and by an EPSRCsupported DTA student. The results of these studies involving RuII pyridyl polyene systems (see (iii) above) have
5
been described to some extent in a previous IGR report, but further data have been obtained and analysed more
recently. These polyene complexes have very large β0 values which cover a range of ca 100–600 × 10–30 esu and
are maximized at n = 2 (where n is the number of E-CH=CH units), in marked contrast to other known D-π-A
polyene chromophores in which β0 increases steadily with n. The Stark results indicate that π →π* ILCT
transitions in the UV region also contribute ca 10% of the overall β0 responses of the n = 2 compounds and ca 20%
for their n = 3 analogues. However, inclusion of these additional contributions to the NLO responses does not alter
the overall conclusion that the β0 values effectively level off or decrease after n = 2. These results are particularly
interesting because they contradict the accepted wisdom that π-conjugation extension enhances NLO responses.1,2
MLCT absorption and electrochemical data clearly show that a {RuII (NH 3 ) 5 } 2+ or related centre is more
electron-rich than a trans-{RuII Cl(pdma)2 }+ [pdma = 1,2-phenylenebis(dimethylarsine)] unit. However, despite
initial assumptions, the β0 values of a series of such arsine complexes determined by using Stark data are only a
little smaller then those of their {RuII (NH 3 ) 5 }2+ analogues. Large molecular quadratic NLO responses are hence
maintained, with considerable gains in visible transparency (the MLCT bands of the arsine complexes are blueshifted by ca 0.6 eV when compared with those of their pentaammine analogues at 77 K), thermal stability and also
crystallising ability. The unusual linear optical behaviour observed with the pyridyl polyene complexes of RuII
ammine centres is also found with the analogous arsine species, but no clear evidence for a corresponding decrease
in β0 on chain extension is observed.
Theoretical Calculations
Calculations on selected RuII ammine pyridyl polyene cations involving time-dependant density-functional theory
(TD-DFT) and the finite field method generally predict the experimentally observed trends, both in terms of the
hypsochromic shifting of the MLCT bands and the maximization of β0 with E,E-buta-1,3-dienyl linkages. The
unexpected optical properties can be rationalised in terms of the extent of orbital overlap between the RuII electron
donor and N-methylpyridinium electron acceptor groups. The TD-DFT results indicate that the HOMO gains in π
character along the two series of complexes and consequently the lowest energy transition usually considered as
MLCT in character has some ILCT contribution that increases with the conjugation pathlength.
RESEARCH IMPACT AND BENEFITS TO SOCIETY
It is not yet possible to assess the impact of the studies supported by this grant because most of the results have yet
to be published (see below). The grant has certainly provided valuable training and experience for Dr Harris,
including visits to carry out Stark spectroscopic measurements at Brookhaven National Laboratory and California
Institute of Technology (CalTech). The broader benefits to society of fundamental research into novel NLO
materials can be expected to become apparent as the technologies for device fabrication and exploitation mature.
EXPLANATION OF EXPENDITURE
Overall spending was within budget, the only minor changes being that a number of small items of equipment were
inadvertantly charged to equipment rather than consumables, and some of the consumables funds were spent on
travel to conferences.
FURTHER RESEARCH OR DISSEMINATION ACTIVITIES
A further full paper (‘Syntheses, Spectroscopic and Quadratic Nonlinear Optical Properties of Extended Dipolar
Complexes with Ruthenium(II) Ammine Electron Donor and N-Methylpyridinium Acceptor Groups’, B J Coe, L A
Jones, J A Harris, B S Brunschwig, I Asselberghs, K Clays, A Persoons, J Garín and J Orduna) has just been
submitted to J. Am. Chem. Soc., and three other full articles are presently in the advanced stages of preparation,
details as follows:
(i) ‘Molecular Quadratic Nonlinear Optical Properties of cis-Tetraammineruthenium(II) Complexes Bearing
Two Pyridinium Electron Acceptor Groups’, B J Coe, L A Jones, J A Harris, B S Brunschwig, K Wostyn, K Clays,
A Persoons, S J Coles and M B Hursthouse, for Dalton Trans.
(ii) ‘Contrasting Linear and Quadratic Nonlinear Optical Behaviour in Ruthenium(II) Ammine and Related
Organic Conjugated Donor-Acceptor Chromophores’, B J Coe, J A Harris, B S Brunschwig, J Garín, J Orduna, S J
Coles and M B Hursthouse, for Chem. Eur. J.
(iii) ‘Syntheses and Optical and Electronic Properties of Iron(II) and Ruthenium(II) Tris-Chelate Complexes
of 2,2′:4,4′′:4′,4′′′-Quaterpyridinium Ligands’, B J Coe, J A Harris and B S Brunschwig, for Dalton Trans.
6
Papers (i) and (ii) may be submitted before the end of 2003, whilst (iii) will be submitted within the next few
months. A further full paper describing RuII arsine complexes, the Stark spectroscopic studies on which were
carried out by Dr Harris, will be submitted to Dalton Trans. at some point later in 2004. Two other conference
poster presentations were given at the Coordination Chemistry Discussion Group Meeting in 2003, but these were
the same as those given at the SPIE Annual Conference and are therefore not listed on page 5 of the IGR form.
The total published output from this grant will comprise of 6 full articles, 2 communications, 3 conference
proceedings and 9 conference oral/poster presentations. Parts of Dr Harris’s studies are now being continued by an
EPSRC-funded DTA student, and an application for continuation funding has just been submitted to EPSRC.
SUMMARY
This grant has allowed us to make considerable progress in our investigations into the NLO properties of transition
metal complexes. Although a number of the original synthetic objectives were not achieved, the available funds
have been put to good use, particularly in making Stark spectroscopic measurements. The highly unusual optical
behaviour observed in the RuII ammine pyridyl polyenes is especially noteworthy, and a number of novel
multidimensional NLO chromophores have also been prepared and studied. Our international collaborations with
Profs Clays and Persoons at Leuven University and Prof Brunschwig at CalTech continue to gain momentum, and
a new collaboration with Prof Garín at Zaragoza University is already producing informative and high-quality
results. Future significant developments from the related work of a DTA student can also be anticipated.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
Nonlinear Optical Properties of Organic Molecules and Crystals, eds. D. S. Chemla and J. Zyss, Academic Press,
Orlando, 1987, vols. 1 and 2; J. Zyss, Molecular Nonlinear Optics: Materials, Physics and Devices, Academic Press,
Boston, 1994; Ch. Bosshard et al., Organic Nonlinear Optical Materials (Advances in Nonlinear Optics, Vol. 1), Gordon
and Breach, Amsterdam, 1995; Nonlinear Optics of Organic Molecules and Polymers, eds. H. S. Nalwa and S. Miyata,
CRC Press, Boca Raton, 1997.
(a) H. S. Nalwa, Appl. Organomet. Chem. 1991, 5, 349. (b) S. R. Marder, in Inorganic Materials, eds. D. W. Bruce and
D. O’Hare, Wiley, Chichester, 1992. (c) D. R. Kanis et al., Chem. Rev. 1994, 94, 195. (d) N. J. Long, Angew. Chem. Int.
Ed. Engl. 1995, 34, 21. (e) I. R. Whittall et al., Adv. Organomet. Chem. 1998, 42, 291 and 43, 349. (f) J. Heck et al.,
Coord. Chem. Rev. 1999, 190–192, 1217. (g) G. M. Gray and C. M. Lawson, in Optoelectronic Properties of Inorganic
Compounds, eds. D. M. Roundhill and J. P. Fackler, Jr., Plenum, New York, 1999, pp. 1–27. (h) S. Shi, in Ibid, pp.
55–105. (i) H. Le Bozec and T. Renouard, Eur. J. Inorg. Chem. 2000, 229. (j) S. Barlow and S. R. Marder, Chem.
Commun. 2000, 1555. (k) P. G. Lacroix, Eur. J. Inorg. Chem. 2001, 339. (l) S. Di Bella, Chem. Soc. Rev. 2001, 30, 355.
(m) B. J. Coe, in Comprehensive Coordination Chemistry II, eds. J. A. McCleverty and T. J. Meyer, Pergamon Press,
Oxford, 2003; Vol. 9, pp. 621–687.
J. L. Oudar and D. S. Chemla, J. Chem. Phys. 1977, 66, 2664; J. L. Oudar, J. Chem. Phys. 1977, 67, 446; E. Hendrickx et
al., J. Am. Chem. Soc. 1995, 117, 3547.
R. W. Terhune et al., Phys. Rev. Lett. 1965, 14, 681; K. Clays and A. Persoons, Phys. Rev. Lett. 1991, 66, 2980; K. Clays
and A. Persoons, Rev. Sci. Instrum. 1992, 63, 3285; E. Hendrickx et al., Acc. Chem. Res. 1998, 31, 675.
W. Liptay, in Excited States, Vol. 1, ed. E. C. Lim, Academic Press, New York, 1974, pp. 129–229; G. U. Bublitz and S.
G. Boxer, Annu. Rev. Phys. Chem. 1997, 48, 213.
(a) B. J. Coe et al., Inorg. Chem. 1997, 36, 3284. (b) B. J. Coe et al., Chem. Commun. 1997, 1645. (c) B. J. Coe et al.,
Inorg. Chem. 1998, 37, 3391. (d) B. J. Coe et al., J. Chem. Soc., Dalton Trans. 1999, 3617. (e) B. J. Coe et al., J. Phys.
Chem. A 2002, 106, 897.
L.-T. Cheng et al., J. Phys. Chem. 1991, 95, 10643.
B. J. Coe et al., Angew. Chem. Int. Ed. 1999, 38, 366; B. J. Coe, Chem. Eur. J. 1999, 5, 2464.
T. Weyland et al., Organometallics 2000, 19, 5235; M. Malaun et al., Chem. Commun. 2001, 49; M. Malaun et al., J.
Chem. Soc., Dalton Trans. 2001, 3025; F. Paul et al., Organometallics 2002, 21, 5229; C. E. Powell et al., J. Am. Chem.
Soc. 2003, 125, 602.
B. J. Coe et al., Chem. Commun. 2001, 1548.
W. M. Laidlaw et al., Nature 1993, 363, 58; Idem, Proc. SPIE, Int. Soc. Opt. Eng. 1994, 2143, 14; I. D. Morrison et al.,
Rev. Sci. Instrum. 1996, 67, 1445.
(a) J. Zyss, I. Ledoux, Chem. Rev. 1994, 94, 77. (b) R. Wortmann et al., Chem. Eur. J. 1997, 3, 1765. (c) A. M.
McDonagh et al., J. Am. Chem. Soc. 1999, 121, 1405.
(a) J. Zyss et al., Chem. Phys. Lett. 1993, 206, 409. (b) C. Dhenaut et al., Nature 1995, 374, 339. (c) F. W. Vance and J.
T. Hupp, J. Am. Chem. Soc. 1999, 121, 4047. (d) H. Le Bozec et al., Synth. Met. 2001, 124, 185. (e) T. Le Bouder et al.,
Chem. Commun. 2001, 2430. (f) H. Le Bozec et al., Adv. Mater. 2001, 13, 1677.
R. J. Morgan and A. D. Baker, J. Org. Chem. 1990, 55, 1986.
A. Ulman, An Introduction to Ultrathin Organic Films: From Langmuir-Blodgett to Self-assembly, Academic Press,
1991; M. C. Petty, Langmuir-Blodgett Films: An Introduction, Cambridge University Press, 1996.
T. Richardson et al., Thin Solid Films 1988, 160, 231; H. Sakaguchi et al., J. Phys. Chem. 1993, 97, 1474.
Selected examples: (a) C. R. Moylan et al., J. Am. Chem. Soc. 1996, 118, 12950. (b) J. J. Wolff et al., Adv. Mater. 1997,
9, 138. (c) M. Tomonari et al., Chem. Phys. Lett. 1997, 266, 488. (d) J. J. Wolff and R. Wortmann, Adv. Phys. Org.
Chem. 1999, 32, 121. (e) Y.-J. Liu et al., J. Mol. Struct. 2001, 570, 43. (f) V. Ostroverkhov et al., Chem. Phys. Lett.
2001, 340, 109. (g) M.-L. Yang and B. Champagne, J. Phys. Chem. A 2003, 107, 3942.
Selected examples: P. G. Lacroix et al., Chem. Mater. 1996, 8, 541; S. Di Bella et al., J. Am. Chem. Soc. 1997, 119,
9550; F. Averseng et al., Chem. Mater. 1999, 11, 995; O. Briel et al., Eur. J. Inorg. Chem. 1999, 483; A. Hilton et al.,
Chem. Commun. 1999, 2521; S. Di Bella et al., Chem. Eur. J. 2001, 7, 3738; S. Di Bella and I. Fragalà, New J. Chem.
2002, 26, 285.