Photoinduced Crystallization in Ionic Liquids: Photodimerization-induced Equilibrium Shift and Crystal Patterning

Abstract

An ionic liquid (IL) composed of 9-anthracenecarboxylate anion and ammonium cation possessing three diethylene glycol chains shows phototriggered dimerization of anthracence chromophores. It causes segregation and crystallization of protonated 9-anthracenecarboxylic acid dimer, which is associated with the concurrent liberation of the free amine in the IL. This work provides a new molecular design for photoresponsive ILs, whose first application for site-selective photopatterning is demonstrated.Ionic liquids (ILs) have attracted considerable interest from many researchers because of their unique physical and chemical properties, which are tunable depending on their constituents. 13One of the evolving areas in this field is the introduction of mesoscopic interfaces 4,5 for developing novel interfacial phenomena. 6,7 In this regard, ILs containing π-conjugated chromophores are attractive as photofunctional soft materials that show new applications such as condensed luminescent materials 810 and solar thermal storage. 11 We have recently reported the photoliquefaction of ionic crystals to ILs by employing cationic azobenzene derivatives covalently modified with three flexible diethylene glycol chains in the ammonium head group. 11 Photon energy was effectively stored not only as the conformational energy of the azobenzene unit but also as the latent heat of crystallization, where the integration of self-assembly phenomena and photoresponsive ILs opened the doors to the phase crossover chemistry. 11Here, we describe a new photoresponsive IL that shows photoinduced crystallization phenomena. It is formed from a well-known Brønsted acid (9-anthracenecarboxylic acid, A-COOH) 12,13 and a Brønsted base having three flexible diethylene glycol chains (tris[2(2methoxyethoxy)ethyl]amine, 1). This integration based on acidbase neutralization gives a chromophoric IL [1-H] +

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

“…Spectral red‐shifts were also detected for the 1 L a absorption band (Figure S7). These results clearly indicate the presence of intermolecular interactions among DPA chromophores in the neat IL state 30. This is in contrast with the highly emissive nonionic liquids reported by Nakanishi et al.…”

“…By changing the solvent polarity from methanol to cyclohexane,t he 1 B b absorption band of the anthracene unit exhibited small band shifts from l = 264 to 267 nm, demonstrating that it was not particularly susceptible to solvent polarity.M eanwhile,t he solvent-free IL 1 showed as ignificantly red-shifted and broadened absorption spectrum with am aximum absorption band at l = 272 nm. [30] This is in contrast with the highly emissive nonionic liquids reported by Nakanishi et al in which the DPAc hromophore is covalently modified with multiple branched alkyl chains. These results clearly indicate the presence of intermolecular interactions among DPAc hromophores in the neat IL state.…”

“…These results clearly indicate the presence of intermolecular interactions among DPAc hromophores in the neat IL state. [30] This is in contrast with the highly emissive nonionic liquids reported by Nakanishi et al in which the DPAc hromophore is covalently modified with multiple branched alkyl chains. [31,32] These nonionic liquids showed almost no spectral shifts from their solutions,r eflecting the isolation of the DPAcores.Considering these differences,itis apparent that the absence of covalently attached alkyl chains to the DPAu nit facilitated interactions between chromophores in IL 1.…”

“…The further visualization of such extended aromatic cluster networks would require the help of molecular modeling techniques,24 which will be implemented in due course. The current work offers an important conceptual bridge between ILs and exciton‐based sciences, which would provide new platforms for the development of optically and electrically active IL materials 30. 39…”

Application of Triplet–Triplet Annihilation Upconversion in Organic Optoelectronic Devices: Advances and Perspectives

“…Recently, Kimizuka and Yanai groups have reported various solid-state TTA upconversion systems. [98,99,[174][175][176][177][178][179][180][181][182][183] A concept of triplet energy migration was proposed to solve the restricted molecular diffusion issue in solid-state environments. [99,182] In 2015, they developed the self-assembled nanofibers as oxygen barrier matrix.…”