Abstract
Luminescent transition metal complexes are introduced for the microcontact printing of optoelectronic devices. Novel ruthenium(II), RubpySS, osmium(II), OsbpySS, and cyclometalated iridium(III), IrbpySS, bipyridyl complexes with long spacers between the surface-active groups and the metal were developed to reduce the distance-dependent, nonradiative quenching pathways by the gold surface. Indeed, surface-immobilized RubpySS and IrbpySS display strong red and green luminescence, respectively, on planar gold surfaces with luminescence lifetimes of 210 ns (RubpySS·Au) and 130 and 12 ns (83%, 17%) (IrbpySS·Au). The modified surfaces show enhancement of their luminescence lifetime in comparison with solutions of the respective metal complexes, supporting the strong luminescence signal observed and introducing them as ideal inorganic probes for imaging applications. Through the technique of microcontact printing, complexes were assembled in patterns defined by the stamp. Images of the red and green patterns rendered by the RubpySS·Au and IrbpySS·Au monolayers were revealed by luminescence microscopy studies. The potential of the luminescent surfaces to respond to biomolecular recognition events is demonstrated by addition of the dominant blood-pool protein, bovine serum albumin (BSA). Upon treatment of the surface with a BSA solution, the RubpySS·Au and IrbpySS·Au monolayers display a large luminescence signal increase, which can be quantified by time-resolved measurements. The interaction of BSA was also demonstrated by surface plasmon resonance (SPR) studies of the surfaces and in solution by circular dichroism spectroscopy (CD). Overall, the assembly of arrays of designed coordination complexes using a simple and direct μ-contact printing method is demonstrated in this study and represents a general route toward the manufacture of micropatterned optoelectronic devices designed for sensing applications.
Highlights
Introduction“Bottom-up” approaches for surface fabrication toward nanoscale devices have flourished in recent years, as “top-down” methods have begun to reach the limits of their potential.[1−5] In particular, microcontact printing (μCP), initially developed by Whitesides,[6,7] allows controlled deposition of molecules on planar substrates such as gold or glass for the fabrication of surfaces for sensing devices for the detection of analytes.[8−11] Photoactive transition metal complexes offer many attractive properties for imaging applications[12−15] including photostability and excitation and emission profiles within the visible region that are more compatible with conventional imaging techniques and larger Stokes shifts (greater than 100 nm)
We have examined the formation of monolayers of ruthenium(II), RubpySS, and cyclometalated iridium(III), IrbpySS, bipyridyl complexes on gold and analyzed their photophysical properties for promising optoelectronic device development (Scheme 1)
The results show that is quenching reduced and the luminescence lifetimes of the complexes are enhanced when the complexes are anchored to gold surfaces
Summary
“Bottom-up” approaches for surface fabrication toward nanoscale devices have flourished in recent years, as “top-down” methods have begun to reach the limits of their potential.[1−5] In particular, microcontact printing (μCP), initially developed by Whitesides,[6,7] allows controlled deposition of molecules on planar substrates such as gold or glass for the fabrication of surfaces for sensing devices for the detection of analytes.[8−11] Photoactive transition metal complexes offer many attractive properties for imaging applications[12−15] including photostability and excitation and emission profiles within the visible region that are more compatible with conventional imaging techniques and larger Stokes shifts (greater than 100 nm). Luminescent thin films have been developed using noncovalent assembly of photoactive metals via Langmuir− Blodgett methods[16,17] or “layer-by-layer” approaches.[18,19] applications of gold surfaces modified with transition metal complexes have been dominated by electrochemical studies[20−22] due to the reported luminescence quenching of the excited state by the gold.[23−25] Despite this, the covalent attachment of metal complexes to gold is attractive as a platform to build recognition sites and develop sensing motifs.
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