Utilizing Polymer-Chromophore Interactions towards Optimizing Triplet-Triplet Annihilation in Solid-State Materials

摘要

Upconversion through triplet-triplet annihilation (TTA) has emerged as a promising anti-Stokes wavelength-shifting technology for applications in which low power sources (i.e. sunlight) are used. Triplet-triplet annihilation upconversion employs a pair of molecules; a sensitizer to absorb the incident light and transfer the energy to emitting species that release photons of higher energy than the excitation source. We have identified Pd(Ⅱ)meso-tetra(4-carboxyphenyl)porphine (PdTCP) as a new sensitizer for this process. This new chromophore has been compared to 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphrine palladium (Ⅱ) (PdOEP), a widely reported sensitizer in systems containing 9,10-diphenyl anthracene (DPA) (the most predominant emitter). The solubility, absorbance, and emission of the chromophores in a DMF solution and polymer systems was evaluated. PdTCP was found to have ca. 20 times greater solubility than PdOEP in DMF solutions. However, optical microscopy and transmission measurements show PdTCP had lower solubility than PdOEP in Tecoflex~®, an aliphatic polyether-based thermoplastic polyurethane. When transitioning from PdOEP to PdTCP, maximum absorbance wavelengths of the Soret and metal to ligand charge transfer bands shift from 391 nm to 417 nm, and 544 nm to 523 nm, respectively. TTA efficiency of the sensitizers was probed in solution and solid-state systems. It was found that in concentrated solutions and Tecoflex~® films PdTCP is less efficient than PdOEP presumably due to increased internal absorption. PdTCP films also exhibited a higher phosphorescence intensity than PdOEP indicating inefficient energetic alignment of the triplet states. The upconversion performance of the PdTCP systems was improved by identifying more compatible polymer matrices.