Revealing the influence of steric bulk on the triplet–triplet annihilation upconversion performance of conjugated polymers

Abstract

A series of poly(phenylene-vinylene)-based copolymers are synthesized using the Gilch method incorporating monomers with sterically bulky sidechains. The photochemical upconversion performance of these polymers as emitters are investigated using a palladium tetraphenyltetrabenzoporphyrin triplet sensitizer and MEH-PPV as reference. Increased incorporation of sterically bulky monomers leads to a reduction in the upconversion efficiency despite improved photoluminescence quantum yield. A phosphorescence quenching study indicates issues with the energy transfer process between the triplet sensitizer and the copolymers. The best performance with 0.18% upconversion quantum yield is obtained for the copolymer containing 10% monomer with bulky sidechains.

Triplet–Triplet Annihilation Upconversion by Polymeric Sensitizers

“…(iii) A large fraction of the DPA annihilators, that is, those in the partial volumes, in which no PS is present, does not participate in the upconversion process. The polymer backbone, which keeps the sensitizer molecules tied, can hinder the free diffusion of sensitizer molecules as well as of DPA molecules by barricading their diffusion path, which may affect the TTET and collisional TTA, ultimately limiting the upconversion emission . (iv) Finally, the compartmentalization of the sensitizer in PS units reduces the upconversion by reabsorption from the first excited singlet state of DPA to PS via Förster resonance energy transfer. ,, When the excitation power density is low and only a few sensitizers are excited, the chances of back energy transfer from localized excited singlet DPA to (non-excited) PS within the “upconversion hot spot” are higher due to the presence of many sensitizers, in the ground state, in the vicinity of a given excited 1 A.…”

Fluorescence of Single Conjugated Chains of MEH‐PPV Dispersed in Polymer Matrix: What Do We See in the Microscope?†

“…[ 1‐5 ] The biggest advantage of CPs is their flexibility, which makes them suitable for flexible and stretchable electronics. [ 6‐9 ] CP‐based solar cells have also attracted increasing attention in recent years due to a series of breakthroughs in efficiency after long‐term stagnation. [ 3,5,10‐13 ] In addition to promising applications, strong fluorescence provides the opportunity to study the photophysics of individual CP chains by single molecule fluorescence spectroscopy.…”