N-置換ジアリールマレイミドおよびその酸化誘導体のフォトクロミズムと凝集誘起発光制御

Chapter 1. Introduction 1. Photochromism -2-2.Photoluminescence -4-2.1 Fluorescence and phosphorescence 2.2 Fluorescence switching 3. Fluorescent switching of diarylethenes and their S,S,S',S'-tetraoxide derivatives -8-3.1 Diarylethenes 3.2 Diarylmaleimides 3.3 Fluorescent diarylethenes containing fluorophores 3.4 Oxidized diarylethene derivatives 3.5 Applications of oxidized diarylethene derivatives 4. Fluorescent switching based on aggregate formation -15-Diarylethene (DAE) is a photochromic compound that undergoes reversible isomerization betweenthe open-ring form (o-form) and the closed-ring form (c-form) solely upon photoirradiation, and exhibits excellent fatigue resistance and thermal stability.Because its photochemical properties can be freely tuned by modifying the ethene unit or the aryl units, DAEs have attracted attention as a promising photoresponsive material.In the present study, aiming at applications to photoresponsive materials for biological use such as bioimaging, we focused on the development of highly polar DAE derivatives capable of fluorescence on/off switching even in aqueous media, specifically on diarylmaleimide (DAM)-S,S,S',S'-tetraoxide derivatives.DAM 1 was designed and synthesized in which a methyl group is introduced at the nitrogen atom of the maleimide, and its tetraoxidized derivative 2, as well as 3 and 4, which possess unsubstituted maleimide at the ethene unit and were designed to allow facile modification of the substituent on the nitrogen atom via the Mitsunobu reaction, and 5 and 6, in which the nitrogen substituent was changed to triethylene glycol monomethyl ether to enhance water solubility.1, 3, and 5 exhibited reversible photochromism upon irradiation at 436 nm and 550 nm in toluene, DCM, and ethanol solutions, and showed turn-off type fluorescence in which the o-form emits very weakly.2, 4, and 6 showed one-way photoisomerization, in which the c-form was produced upon irradiation at 365 nm in toluene and DCM solutions, whereas ethanol solutions exhibited two-way photoisomerization, undergoing cyclization upon 365-nm irradiation and cycloreversion upon 436-nm irradiation.These results demonstrate that the directionality of photoisomerization can be switched between one-way and two-way depending on the solvent polarity.In contrast to 1, 3, and 5, tetraoxide derivatives 2, 4, and 6 showed turn-on type fluorescence in all solvents examined, in which the c-form emits yellow fluorescence.In 75% water/ethanol mixed solution, the c-form formed aggregates and exhibited green fluorescence distinct from that observed in the molecularly dispersed state, demonstrating that the emission color can be switched by aggregation.Among 2, 4, and 6, 6 formed the largest and fastest-growing aggregates and exhibited aggregation-induced emission enhancement (AIEE) accompanied by a pronounced blue shift.DAM-S,S,S',S'-tetraoxide derivatives that show distinct fluorescence colors in the solution and aggregated states, together with AIEE provide new insights into the molecular design of multicolor and multistate photoresponsive materials.Because AIEE is expected to have wide-ranging applications in bioimaging, chemical sensing, and organic electronics, the present results also indicate the potential applicability of these compounds in such fields.