Postsynthetic Systematic Electronic Tuning of Organoplatinum Photosensitizers via Secondary Coordination Sphere Interactions

Abstract

In this work we show that postsynthetic addition of borane Lewis acids to Lewis base decorated organoplatinum photosensitizers induces significant changes in the optical and electrochemical properties. In particular, the charge transfer (CT) energies of these chromophores are significantly modified by these outer-sphere interactions. The direction of the CT shift depends on the site of Lewis acid binding, which occurs either at the diimine ligand in bipyrazine-linked molecules or at an ancillary acetylide ligand in pyridyl-substituted bis­(acetylide) molecules. The magnitude of the shift depends on the Lewis acidity of the borane and the number of equivalents added and is comparable to the perturbation brought on by covalent substituent modification of supporting ligands in related complexes. This approach offers a new means of tuning the properties of organometallic phosphors that complements the traditional approach of covalent modification and other postsynthetic modification strategies.

Facile Synthesis of Luminescent Ir–Pt–Ir Trimetallic Complexes

“…These new bands arise from perturbed acetylide‐centered transitions. A similar phenomenon was observed when a closely‐related analogue of 3 (without 4,4′‐di‐tert‐butyl substitution) was coordinated to Lewis acidic boranes via the pyridylacetylide ligands . This indicates that orbitals and electronic transitions originally localized on the Pt fragment are perturbed upon coordination of two Lewis acidic [Ir(C^N) 2 ] + fragments and suggests some degree of electronic communication between the components.…”

“…This blueshift in λ max is consistent with stabilization of occupied Pt dπ orbitals caused by the Lewis acidic Ir metal center acting as an electron‐withdrawing group. These observations are reminiscent of our recent work where coordination of boranes by pyridyl‐substituted platinum acetylide complexes perturbs the energy of the excited state and alters the excited‐state character …”

“…This complex has a short excited‐state lifetime that is best fit as a bi‐exponential decay with time constants of 36 ns (94 %) and 5.5 ns (6 %). The major component of the emission spectrum at room temperature is fairly similar to the spectrum observed when an analogue of 3 is bound to two equivalents of triarylboranes …”

“…The first reduction potentials of all trimetallic complexes ( 4 a – 4 c ) were slightly shifted positive by 50–70 mV compared to that of the Pt monometallic complex 3 , because of the electron‐withdrawing effect of the Ir centers. A similar effect is observed when Lewis acidic boranes coordinate to an analogue of complex 3 via pyridylacetylide ligands . All these observations clearly indicate some perturbation of the electronic structure of individual units in the multinuclear systems and support the observed results in UV/Vis absorption spectroscopy experiments.…”

Lewis Acid Modulation of meso‐Pyridyl BODIPY Chromophores

“…For certain applications, especially solar cells where the precise absorption profile is critical or OLEDs where the emission color is a key determinant in device performance, the ability to rapidly, systematically, and precisely control the optical properties would be a significant advantage. Our group has recently introduced the concept that Lewis acid‐base interactions in the secondary coordination sphere can modulate the photophysical properties of organometallic phosphors, allowing rapid and facile color‐tuning of the emission over a wide range . In this previous work we showed that boranes, which are available with numerous substituents that can engender a wide range of available Lewis acidities, allow precise control over the electronic structure.…”