Ionic Liquid Dependence of Triplet-Sensitized Photon Upconversion

Abstract

Photon upconversion (UC) is a technology used to convert wasted lower energy photons to usable higher energy photons. Triplet-sensitized UC based on the triplet-triplet annihilation (TTA) of organic molecules has recently received attention because of its applicability to noncoherent sunlight. Among the various media proposed for this UC, ionic liquids (ILs) are practically advantageous because of their nonvolatility and nonflammability. However, from previous studies, the efficiency of UC (ΦUC) has been found to depend on the ILs employed. In this article, systematic investigations were carried out on samples made using more than 10 kinds of ILs, all of which were purified before sample fabrication to enhance data reliability. Several clear tendencies were found, and they were all related to the viscosity of the ILs. We also found that the magnitude of their solvatochromic shifts did not correlate to these trends. These results show that the dynamic aspects of the molecules influence the kinetics that govern the magnitude of ΦUC. Along with related discussions and interpretations, these results should provide a guideline toward increasing the ΦUC.

Visible-to-ultraviolet (<340 nm) photon upconversion by triplet–triplet annihilation in solvents

“…† We included D-limonene because it has been reported to prevent degradation of solutes in visible-to-visible UC by functioning as a strong antioxidant that quickly scavenges residual oxygen. 60 Additionally, in the former half of this study, we included the ionic liquid [C 4 dmim][NTf 2 ] as a reference solvent because it enables highly stable red-to-blue UC 16,[21][22][23] (Fig. S1, ESI †).…”

“…50 Previously, we reported visible-to-visible UC in systems using an ionic liquid as the solvent. 16,[21][22][23]28 These samples, when properly sealed, exhibited excellent photostability and their lifetime exceeded several years (Section S1 of the ESI †). However, when the same ionic liquid was combined with the sensitizer and emitter used in the present study for UV-UC ( Fig.…”

Photon‐Upconverting Ionic Liquids: Effective Triplet Energy Migration in Contiguous Ionic Chromophore Arrays

“…Interestingly,t he TTA-UC process in the chromophoric IL was optimizedatamuch lower excitation intensity compared to the previous nonionic liquid TTA-UC system. To develop nonvolatile TTA-UC systems, previous approaches introduced rubbery polymers [14][15][16][17][18] or involatile liquids [6,7,19,20] as matrices for the diffusion of molecules in the triplet excited state.H owever,m olecular diffusion is inevitably limited in these viscous environments, which consequently required an undesirably high intensity of excitation light. [1][2][3][4][5][6][7][8][9][10][11][12][13] AT TA-UC system consists of triplet donors (sensitizers) and acceptors (emitters), as shown schematically in Figure S1 in the Supporting Information.…”

“…Thec ollision of two triplet acceptors,p opulated by triplet-triplet energy transfer (TTET) from photoexcited donors,l eads to TTA within the lifetimes of the acceptor triplets.T he annihilation generates ah igher-energy excited singlet state,f rom which upconverted delayed fluorescence occurs.Because the TTET and TTAprocesses proceed via an electron-exchange Dexter mechanism, the excited triplet molecules need to be in close proximity to each other, within ad istance of 1nm, to allow the overlap of molecular orbitals.Although efficient TTA-UC has been achieved by using fast molecular diffusion in solutions, [1,9,10] the use of such volatile organic solvents significantly hampers their realworld application. To develop nonvolatile TTA-UC systems, previous approaches introduced rubbery polymers [14][15][16][17][18] or involatile liquids [6,7,19,20] as matrices for the diffusion of molecules in the triplet excited state.H owever,m olecular diffusion is inevitably limited in these viscous environments, which consequently required an undesirably high intensity of excitation light. An innovative solution for these issues is to change the strategy from molecular diffusion to energy migration among dye assemblies.…”

Dye functionalized-ROMP based terpolymers for the use as a light up-converting material via triplet–triplet annihilation

“…The first examples were prepared in 2007 by the working group of Castellano et al and they used blends of Pd 2,3,7,8,12,13,17,18-octaethylporphyrin (PdOEP) as sensitizer and diphenylanthracene (DPA) as emitter in an ethylene oxide/ epichlorohydrin copolymer to obtain a rubber like matrix. 19 Recent studies show that this effect is also possible with active polymeric structures, [20][21][22][23][24][25] liposomes, 26,27 ionogels, 28 oil in water micro emulsions, [29][30][31] micelles, 17 dendrimers, 32 nanocapsules, [33][34][35] and many more. 1,7,36 The translational and rotational mobility of the chromophores is essential for an efficient photon light up-converting process, due to the fact that mobility influences all the implemented energy transfer processes.…”