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|Title:||Impact of molecular conformation on triplet-fusion induced photon energy up-conversion in the absence of exothermic triplet energy transfer||Authors:||Goudarzi, Hossein
Zenonos, Vassiliki M.
Keivanidis, Panagiotis E.
|Major Field of Science:||Engineering and Technology||Field Category:||Environmental Engineering||Keywords:||Energy transfer;Photoluminescence spectroscopy;Spectroscopic analysis;Absorption spectroscopy||Issue Date:||2019||Source:||Journal of Materials Chemistry C, 2019, vol. 7, no. 12, pp. 3634-3643||Volume:||7||Issue:||12||Start page:||3634||End page:||3643||Journal:||Journal of Materials Chemistry C||Abstract:||The use of photon energy up-converted luminescence driven by triplet-exciton annihilation reactions (TTA-UC) is increasingly gaining attention for developing next-generation light-management, and wavelength-shifting technologies. Here we present a spectroscopic study for elucidating the photophysical mechanism that operates in an unusual TTA-UC model system comprising the blue-light emitting poly(fluorene-2-octyl) (PFO) activator mixed with the green-light absorbing (2,3,7,8,12,13,17,18-octaethyl-porphyrinato) Pt II (PtOEP) metalo-organic complex. The unconventional character of the PFO:PtOEP composite manifests in the fact that no exothermic triplet energy transfer (TET) is possible between triplet-excited PtOEP and PFO. Yet green-to-blue TTA-UC luminescence of PFO is obtained even when PtOEP is selectively photoexcited by pulsed laser intensities as low as 2.5 mW cm −2 . Continuous-wave photo-induced absorption spectroscopy verifies that no energy transfer from triplet-excited PtOEP to the triplet level of PFO takes place, pointing to triplet-triplet annihilation (TTA) events in the PtOEP phase as the origin of the observed TTA-UC PL signal. In the PFO:PtOEP composite, the PtOEP component holds a dual role of annihilator/sensitizer; photon energy storage in PtOEP is enabled via TTA when triplet exciton diffusion coefficient values of D PtOEP = 4.1 × 10 −9 cm 2 s −1 are reached. With a simple yet powerful solution processing protocol, and by combining Raman and time-gate photoluminescence (PL) spectroscopy we demonstrate that the brightness of the produced TTA-UC luminescence depends on the molecular conformation of the PFO activator. A four-fold increase in the TTA-UC luminescence intensity is registered in the time-integrated and time-gated PL spectra, when the PFO matrix is arrested in its planar β-phase molecular conformation. Further enhancement of the TTA-UC PL signal is achieved when temperature lowers from 290 K down to 100 K. These results stimulate the development of a theoretical model for the microscopic description of triplet exciton migration in disordered photon up-converting solids. Efficient harvesting of photon energy, which is stored in annihilator/sensitizer moieties via TTA events, can be enabled when the molecular conformation of the activator species is properly tuned.||ISSN:||2050-7534||DOI:||10.1039/c8tc06283h||Collaboration :||Fondazione Istituto Italiano di Tecnologia
Imperial College London
Ciudad Universitaria de Cantoblanco
Cyprus University of Technology
|Rights:||© The Royal Society of Chemistry||Type:||Article|
|Appears in Collections:||Άρθρα/Articles|
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