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. 2014 May 27;33(10):2467-2478.
doi: 10.1021/om401153x. Epub 2014 May 8.

Surface-Bound Ruthenium Diimine Organometallic Complexes: Excited-State Properties

Geoffrey Abbott  1 , Robert Brooks  1 , Edward Rosenberg  1 , Michelle Terwilliger  1 , J B Alexander Ross  1 , Ogar O L Ichire  1
Affiliations

Surface-Bound Ruthenium Diimine Organometallic Complexes: Excited-State Properties

Geoffrey Abbott et al. Organometallics. .

Abstract

Ruthenium complexes of the general formula [Ru(CO)(H)(L2)(L'2)][PF6] (L2 = trans-2PPh3, L' = η2-4,4'-dicarboxybipyridine (1); L2 =trans-2Ph2PCH2CH2COOH, L'2 = bipyridine (2); L2 = Ph2PCHCHPPh2, L' = η2-5-amino-1,10-phenanthroline (3); L2 = trans-2PPh3, L'2 = η2-4-carboxaldehyde-4'-methylbipyridine (4)) have been shown to have longer emission lifetimes and higher quantum yields in solution compared with more symmetrical molecules such as [Ru(bpy)3][Cl]2. Compound 4 is obtained as a mixture with the corresponding acetal, 4'. These less symmetrical complexes have been covalently immobilized on the surface of silica polyamine composites, and their photophysical properties have been studied. The surface-bound complexes have been characterized by solid-state CPMAS 13C, 31P, and 29Si NMR, UV-vis, and FT-IR spectroscopies. Excited-state lifetime studies revealed that, in general, the lifetimes of the immobilized complexes are 1.4 to 8 times longer than in solution and are dependent on particle size (300-500 μm versus 10-20 nm average diameter silica gels), polymer structure (linear poly(allylamine) versus branched poly(ethylenimine)), and the type of surface tether. One exception to this trend is the previously reported complex [Ru(bpy)2(5-amino-1,10-phenanthroline)][PF6]2 (5), where only a slight increase in lifetime is observed. Only minor changes in emission wavelength are observed for all the complexes. This opens up the possibility for enhanced heterogeneous electron transfer in photocatalytic reactions.

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Figures

Scheme 1
Scheme 1. Synthesis of Silica Polyamine Composites
Chart 1
Chart 1. Structures of the Ruthenium Complexes Studied
Scheme 2
Scheme 2. Coupling of 1 and 2 to BP-1
Scheme 3
Scheme 3. Coupling of 3 and 5 to BP-1
Scheme 4
Scheme 4. Coupling of 4 and/or 4′ to BP-1
Figure 1
Figure 1
Comparison of metal–CO IR stretching frequency between (a) compound 1 as a KBr pellet and the analogue (MPA-1) on the BP-1 surface (b).
Figure 2
Figure 2
CPMAS 31P solid-state NMR of MPA-3 at 202.5 MHz.
Figure 3
Figure 3
CPMAS–29Si SS-NMR showing the resonance peak differences between bulk and surface silanes.
Figure 4
Figure 4
(a) 13C of NPA prior to reaction with complex 3. (b) 13C of NPA after reaction with complex 3 showing loss of the aminopropyl groups. (c) 29Si SS-NMR of NPA prior to reaction with complex 3. (d) 29Si SS-NMR after reaction with complex 3 showing loss of Tn sites.
Figure 5
Figure 5
Bar graph showing the loading levels of complexes 1–3 on micro and nano SPCs.
Figure 6
Figure 6
Graph showing the loading levels of complex 2 on reaction with NPA.
Figure 7
Figure 7
Absorption spectra of complex 1: in solution (----); on the composite BP-1 (MPA-1) (—).
Figure 8
Figure 8
Top: Peak normalized emission spectra of complex 2 in solution (—) and on the composite BP-1 (MPA-2) (----). Bottom: Excitation spectra of complex 2 in solution (—) and on the composite BP-1 (MPA-2) (----).
Figure 9
Figure 9
Close-packed sphere models of complexes 5, 1, and 3.
Scheme 5
Scheme 5. Lifetimes of Complex 3 on Different Surfaces
Figure 10
Figure 10
Lifetime decay curve for MPA-1, with a fitted average lifetime of 3.45 μs.
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