Syntheses and Study Toward Excited-State Proton Transfer Molecules and Syntheses of Energy Storage Molecules

• Main Authors: Fan-Yi Meng, 孟繁翌
• Other Authors: 周必泰
• Format: Others
• Language: en_US
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/j6gma4

博士 === 國立臺灣大學 === 化學研究所 === 107 === Chapter 1. The N-H Type Excited-State Proton Transfer Possessing Seven-Membered Ring Intramolecular Hydrogen Bond A series of compounds bearing 5-(2-aminobenzylidene)-2,3-dimethyl-3,5-dihydro-4H-imidazol-4-one (o-ABDI) as the core chromophore possessing a seven-membered ring N-H type intramolecular hydrogen bond (H-bond) are synthesized and characterized. The acidity of the N-H proton and thus the H-bond strength can be fine-tuned by replacing one of the amino hydrogen atoms by a –R substituent, being increased upon increasing the electron withdrawing strength of -R in the order of -H < -COCH3 < -COPh < -Tosyl < -COCF3. Tosyl and trifluoroacetyl derivatives undergo ultrafast, irreversible excited-state intramolecular proton transfer (ESIPT), resulting in solely the proton-transfer emission in the red. Reversible type of ESIPT and hence dual emissions, consisting of normal and proton-transfer tautomer, is resolved for acetyl and benzyl substituted counterparts. As for the weakest acidity in o-ABDI, ESIPT is prohibited due to its highly endergonic reaction. The results clearly demonstrate the harnessing of ESIPT properties via proton acidity and H-bonding strength in a seven-membered ring intramolecular H-bond system. For all studied compounds the emission quantum yield is weak (~10-3) in dichloromethane but is strong in solid ranging from 3.2% to 47.4 %. Chapter 2. Syntheses and Excited-State Intramolecular Proton Transfer of 3-Hydroxythioflavone and Its Sulfone Analogue 3-hydroxythioflavone (3-HTF) was synthesized by oxidation with selenium dioxide, as contrast with 3-hydroxyflavone, a prototype molecule undergoing excited-state intramolecular proton transfer (ESIPT) reaction. Also achieved were syntheses of 3-HTF sulfone analogue and an interesting sulfonyl selane intermediate with their structures fully characterized. 3-HTF showed an ultrafast ESIPT property, as evidenced by > (150 fs)-1 reaction rate constant as well as exhibiting solely a proton-transfer tautomer emission (590 nm) in cyclohexane at RT and in 77 K solid matrix. The lower electronegativity of sulfur atom in 3-HTF leads to significant red shift of the tautomer emission compared with that of 3-hydroxyflavone. The sulfone analogue showed lack of ESIPT due mainly to the decrease of carbonyl basicity, and break the aromaticity of heterocyclic ring. Chapter 3. Molecular Energy Storage Exploiting Thermally Activated Delayed Fluorescence Molecules exhibiting thermally activated delayed fluorescence (TADF) possess proximal energy level between the lowest lying excited singlet (S1) and triplet (T1) states. Thus, the energy level of their T1 state can be readily assessed once knowing either S0 → S1 absorption or S0 ← S1 emission gap. This benefits application of TADF molecules utilizing the triple state as a sensitizer for energy transfer. On this basis, we report the new concept that utilizes a thermally activated delayed fluorescence (TADF) core phenoxazine–triphenyltriazine (PX-TZ) coupled with norbornadiene (NBD), (1s,4s)-bicyclo[2.2.1]hepta-2,5-diene, to form an efficient energy storage diad PXTZ-NBD. PXTZ-NBD exhibits an optimum absorption that covers the solar spectrum up to 460 nm. Upon exciting PXTZ-NBD, PXTZ serves as a sensitizer to sensitize NBD triplet state via triplet-triplet energy transfer, followed by the conversion of NBD to a quadricyclane system (QC), namely tetracyclo[3.2.0.02,7.04,6]heptane, forming a PXTZ-QC product that is thermally stable but convertible back to PXTZ-NBD promptly via catalytic reaction. The uniqueness lies in that the degree of photo-conversion and thermal-reverse-conversion can be directly monitored by TADF in both intensity and relaxation dynamics. The PXTZ-NBD ↹ PXTZ-QC photo-thermal conversion renders the energy storage densities of 177 kJ/mol with good durability evidenced by negligible side products after five photo-thermal conversion cycles. This generates a TADF based solar-thermal energy storage system, for which optimal (≤ 460 nm) solar energy is harvested.