Tetraphenylethene-Based Emissive Pt(II) Coordination Polymer toward Artificial Light-Harvesting Systems with Sequential Energy Transfer
Shakil Ahmed, Atul Kumar, Partha Sarathi Mukherjee
Abstract
Supramolecular systems with sequential energy transfer have prospects in designing artificial light-harvesting systems (LHSs), which can mimic natural photosynthesis process. Here, we report a facile synthesis of a supramolecular coordination polymer (SCP) P as an emissive material through two-component coordination-driven self-assembly of a tetra-imidazole donor (L) containing tetraphenylethene backbone with a 180° trans-[Pt(PEt3)2(OTf)2] acceptor. P shows considerable enhancement in its emission in 90% water–DMSO mixture as it further self-assembles into spherical nanoaggregates. In addition, because of the framework structure of P with hydrophobic cavities and the interspaces present in the nanoaggregates of P, it can act as a suitable host to adsorb organic dyes. Therefore, polymeric material P in the nanoaggregate form in aqueous–DMSO medium was used as an efficient platform to fabricate two highly efficient light-harvesting materials with rare two-step cascade energy-transfer process. For the first-step energy-transfer process, P acts as an efficient energy donor by the Förster resonance energy-transfer (FRET) process to Eosin Y (EY) and Fluorescein (Fl) with high energy-transfer efficiency (58.8% for P-EY and 67.9% for P-Fl), good antenna effect (7.2 for P-EY, 5.2 for P-Fl), and increased quantum yield. Moreover, NiR (Nile Red) was used as a second acceptor to construct efficient two-step artificial light-harvesting materials (P-EY-NiR and P-Fl-NiR), which exhibit high FRET efficiencies of 68.5 and 76.2% as well as good antenna effect of 10.9 and 17.7, respectively. These light-harvesting materials represent the new examples of artificial LHSs based on nanoaggregates of an SCP with sequential two-step energy transfer in aqueous medium. Notably, emission/visual color changes from blue to yellow to pink for P-EY-NiR and blue to green to pink for P-Fl-NiR and cover the entire visible range spectrum.