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

Abstract

Inspired by the bicontinuous ionic-network structure of ionic liquids (ILs), we developed a new family of photofunctional ILs which show efficient triplet energy migration among contiguously arrayed ionic chromophores. A novel fluorescent IL, comprising an aromatic 9,10-diphenylanthracene 2-sulfonate anion and an alkylated phosphonium cation, showed pronounced interactions between chromophores, as revealed by its spectral properties. Upon dissolving a triplet sensitizer, the IL demonstrated photon upconversion based on triplet-triplet annihilation (TTA-UC). Interestingly, the TTA-UC process in the chromophoric IL was optimized at a much lower excitation intensity compared to the previous nonionic liquid TTA-UC system. The superior TTA-UC in this IL system is characterized by a relatively high triplet diffusion constant (1.63×10(-6) cm(2) s(-1)) which is ascribed to the presence of ionic chromophore networks in the IL.

Visible‐to‐UV Photon Upconversion in Nanostructured Chromophoric Ionic Liquids

“…This was also supported by the absence of sharp peaks in its synchrotron powder X‐ray diffraction (PXRD) pattern (Figure d). The PXRD pattern also indicated the existence of the bicontinuous network nanostructures in P 66614 PPOS composed of polar ionic and nonpolar alkyl/chromophore domains . The low‐angle peak at 2.7° of P 66614 PPOS was in accordance with those of the precursor IL P 66614 Cl and our previous blue‐emitting chromophoric IL having the same P 66614 cation .…”

“…The PXRD pattern also indicated the existence of the bicontinuous network nanostructures in P 66614 PPOS composed of polar ionic and nonpolar alkyl/chromophore domains . The low‐angle peak at 2.7° of P 66614 PPOS was in accordance with those of the precursor IL P 66614 Cl and our previous blue‐emitting chromophoric IL having the same P 66614 cation . The distance of 1.75 nm corresponds to the separation between the ionic domains, which is mainly determined by the size of the bulky cation …”

“…In this work, we report the first IL that exhibits vis‐to‐UV TTA‐UC (Figure a). We have recently reported the green‐to‐blue TTA‐UC with low I th in chromophoric ILs, where the acceptor chromophore arrays in the nonpolar IL domain allow effective triplet exciton diffusion . Based on this concept, we designed a new IL composed of flexible alkyl‐chained cation trihexyltetradecylphosphonium (P 66614 ) and UV‐emitting anion 4‐(2‐phenyloxazol‐5‐yl)benzenesulfonate (PPOS) (Figure b).…”

Triplet transport in thin films: fundamentals and applications

“…In order to realize a much closer stacking of the emitter, Hisamitsu et al used ionic liquids (ILs) that contain closely packed charged chromphores. 105 In their work, the sulfonated DPA anion IL1 (Fig. 7) was used with an alkylated phosphonium countercation, eliminating alkyl chains.…”

Photo-induced electron transfer in a diamino-substituted Ru(bpy)3[PF6]2 complex and its application as a triplet photosensitizer for nitric oxide (NO)-activated triplet—triplet annihilation upconversion

“…9−11 Only non-coherent, dim light is required for TTA upconversion, and it has been shown that photoexcitation power densities as low as only a few mW cm −2 is sufficient, such that solar irradiation can also be used. 12,13 Since TTA upconversion systems typically exhibit strong absorption of photoexcitation, upconversion quantum yields as high as 20−30% can be achieved. Furthermore, absorption and emission wavelengths can be synthetically tuned, 1,2 and upconversion system can be readily tagged to various matrices, including nanoparticles, 14 microemulsions, 15 and microcapsules.…”