Abstract
Designing artificial light harvesting systems with the ability to utilize the output energy for fruitful application in aqueous medium is an intriguing topic for the development of clean and sustainable energy. We report here facile synthesis of three prismatic molecular cages as imminent supramolecular optoelectronic materials via two-component coordination-driven self-assembly of a new tetra-imidazole donor (L) in combination with 180°/120° di-platinum(ii) acceptors. Self-assembly of 180° trans-Pt(ii) acceptors A1 and A2 with L leads to the formation of cages Pt4L2(1a) and Pt8L2(2a) respectively, while 120°-Pt(ii) acceptor A3 with L gives the Pt8L2(3a) metallacage. PF6− analogues (1b, 2b and 3b) of the metallacages possess a high molar extinction coefficient and large Stokes shift. 1b–3b are weakly emissive in dilute solution but showed aggregation induced emission (AIE) in a water/MeCN mixture as well as in the solid state. AIE active 2b and 3b in aqueous (90% water/MeCN mixture) medium act as donors for fabricating artificial light harvesting systems via Förster resonance energy transfer (FRET) with organic dye rhodamine-B (RhB) with high energy efficiency and good antenna effect. The metallacages 2b and 3b represent an interesting platform to fabricate new generation supramolecular aqueous light harvesting systems with high antenna effect. Finally, the harvested energy of the LHSs (2b + RhB) and (3b + RhB) was utilized successfully for efficient visible light induced photo-oxidative cross coupling cyclization of N,N-dimethylaniline (4) with a series of N-alkyl/aryl maleimides (5) in aqueous acetonitrile with dramatic enhancement in yields compared to the reactions with RhB or cages alone.
Highlights
In nature, the photosynthesis process of harvesting solar light and its transformation to chemical energy plays a crucial role in development of life
The process of harvesting light in photosynthesis critically relies on excitation energy migration from the light absorbing pigment ‘chlorophyll’ which is embedded in light harvesting complexes known as antenna proteins to the reaction center ‘carotenoid’ where light energy is utilized for the eventual conversion into chemical energy.[1]
Desired ligand L was synthesized by allylic coupling of imidazole with 1,1,2,2-tetrakis(4-(bromomethyl)phenyl)ethene C1 in Scheme 1 Schematic representation of the formation of Pt(II) metallacages using a flexible tetra-imidazole donor
Summary
The photosynthesis process of harvesting solar light and its transformation to chemical energy plays a crucial role in development of life. Both 1H and 31P NMR suggest that chemical shi s of 2b remain unaffected and only an increase in the 1H signal of RhB was observed upon its gradual addition (up to six equivalents with respect to 2b) to a cage solution of 2b (Fig. S20 and S21†).
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