목차

1. Chemical Abbreviations
   Table List
   Figure List
   Scheme List
   Ⅰ. Introduction 1
   1. ortho-Carborane 1
   2. 2,1,3-Benzothiadiazole 2
   3. Thermally activated delayed fluorescence (TADF) 2
   4. References 4
   Ⅱ. The Control of Radiative Efficiency Based on Intramolecular Charge Transfer by Structural
   Rigidity 6
   1. Introduction 6
   2. Results and Discussion 9
   1) Synthesis and Characterization 9
   2) Photophysical properties for o-carboranyl luminophores with computational calculations 11
   3) Comparative analysis for the ICT-based radiative decay of o-carboranyl compounds
   in the solid state 18
   4) TADF characteristics revealed by rigid structural formation 21
   5) Electrochemical and thermal stabilities of the o-carboranyl compounds 24
   3. Experiment Section 27
   1) Synthesis 27
   2) NMR data 36
   3) UV-Vis absorption and photoluminescence (PL) measurements 50
   4) X-ray crystallography 51
   5) Computational calculation studies 53
   4. Conclusions 64
   5. References 65
   Ⅲ. The Control of Radiative Efficiency Based on Intramolecular Charge Transfer by
   Electronic Environment of Donor 68
   1. Introduction 68
   2. Results and Discussion 70
   1) Synthesis and Characterization 70
   2) Photophysical property analyses and theoretical calculations 73
   3) Quantitative analysis of ICT-based radiative decay using dipole moment calculations 76
   3. Experiment Section 80
   1) Synthesis 80
   2) NMR data 93
   3) UV-Vis absorption and photoluminescence (PL) measurements 123
   4) X-ray crystallography 123
   5) Computational calculation studies 126
   4. Conclusions 145
   5. References 146
   Ⅳ. The Control of Radiative Efficiency Based on Intramolecular Charge Transfer by
   Heteroatom Position 149
   1. Introduction 149
   2. Results and Discussion 152
   1) Synthesis and Characterization 152
   2) Photophysical property analyses and theoretical calculations 153
   3) Mechanochromic fluorescence behaviors of αCB, βCB, and γCB originating
   from the solvation effect 159
   3. Experiment Section 164
   1) Synthesis 164
   2) NMR data 167
   3) UV-Vis absorption and photoluminescence (PL) measurements 170
   4) X-ray crystallography 170
   5) Computational calculation studies 173
   4. Conclusions 185
   5. References 186
   Table List
   Table 2-1. Photophysical data for 2FC, 3FC, 4FC, nido-4FC, and 4FCH 12
   Table 2-2. The C–C bond lengths (Å) within the o-carborane cages of 2FC, 3FC, 4FC, and 4FCH, along with the corresponding dihedral angles (Ψ /°) between the C‒C bonds of the o-carborane cages (designated as C14‒C15 in X-ray crystal structures) and the fluorene planes 15
   Table 2-3. Crystallographic data and parameters for 2FC, 3FC, 4FC, and 4FCH 52
   Table 2-4. Selected angles (°) and bond lengths (Å) of 2FC, 3FC, 4FC, and 4FCH 53
   Table 2-5. Calculated oscillator strengths (fcalc) and absorption wavelengths (λcalc in nm) of 2FC from TD-PBE0 calculations using the PBE0 geometries at both S0-state and the S1-state fully optimized geometries in THF 56
   Table 2-6. Molecular orbital distributions (in %) and energies (in eV) of 2FC at both S0-state and the S1-state fully optimized geometries in THF 57
   Table 2-7. Calculated oscillator strengths (fcalc) and absorption wavelengths (λcalc in nm) of 3FC from TD-PBE0 calculations using the PBE0 geometries at both S0-state and the S1-state fully optimized geometries in THF 59
   Table 2-8. Molecular orbital distributions (in %) and energies (in eV) of 3FC at both S0-state and the S1-state fully optimized geometries in THF 60
   Table 2-9. Calculated oscillator strengths (fcalc) and absorption wavelengths (λcalc in nm) of 4FC from TD-PBE0 calculations using the PBE0 geometries at both S0-state and the S1-state fully optimized geometries in THF 62
   Table 2-10. Molecular orbital distributions (in %) and energies (in eV) of 4FC at both S0-state and the S1-state fully optimized geometries in THF 63
   Table 3-1. Dihedral angles between the two biphenyl rings (Ψbp = C5–C6–C9–C10) and those
   between the C‒C bond axis in the o-carborane cage and phenyl plane (Ψax = C1–C2–C3–C4), as well as the bond lengths (C1–C2) of the C‒C bonds in the cage of 1T‒6O 72
   Table 3-2. Photophysical data for 1T‒6O 74
   Table 3-3. Crystallographic data and parameters for biphenyl appended o-carborane compounds (1T–3H) 124
   Table 3-4. Crystallographic data and parameters for biphenyl appended o-carborane compounds (4M–6O) 125
   Table 3-5. Selected angles (°) and bond lengths (Å) of biphenyl appended o-carborane compounds 126
   Table 3-6. Calculated oscillator strengths (fcalc.) and absorption wavelengths (λcalc in nm) of 1T from TD-CAM-B3LYP calculations using the CAM-B3LYP geometries at both S0-state and the S1-state optimized geometries in THF 128
   Table 3-7. Molecular orbital distributions (in %) and energies (in eV) of 1T at both S0-state and the S1-state fully optimized geometries in THF 129
   Table 3-8. Calculated oscillator strengths (fcalc.) and absorption wavelengths (λcalc in nm) of 2F from TD-CAM-B3LYP calculations using the CAM-B3LYP geometries at both S0-state and the S1-state optimized geometries in THF 131
   Table 3-9. Molecular orbital distributions (in %) and energies (in eV) of 2F at both S0-state and the S1-state fully optimized geometries in THF 132
   Table 3-10. Calculated oscillator strengths (fcalc.) and absorption wavelengths (λcalc in nm) of 3H from TD-CAM-B3LYP calculations using the CAM-B3LYP geometries at both S0-state and the S1-state optimized geometries in THF 134
   Table 3-11. Molecular orbital distributions (in %) and energies (in eV) of 3H at both S0-state and the S1-state fully optimized geometries in THF 135
   Table 3-12. Calculated oscillator strengths (fcalc.) and absorption wavelengths (λcalc in nm) of 4M from TD-CAM-B3LYP calculations using the CAM-B3LYP geometries at both S0-state and the S1-state optimized geometries in THF 137
   Table 3-13. Molecular orbital distributions (in %) and energies (in eV) of 4M at both S0-state and the S1-state fully optimized geometries in THF 138
   Table 3-14. Calculated oscillator strengths (fcalc.) and absorption wavelengths (λcalc in nm) of 5B from TD-CAM-B3LYP calculations using the CAM-B3LYP geometries at both S0-state and the S1-state optimized geometries in THF 140
   Table 3-15. Molecular orbital distributions (in %) and energies (in eV) of 5B at both S0-state and the S1-state fully optimized geometries in THF 141
   Table 3-16. Calculated oscillator strengths (fcalc.) and absorption wavelengths (λcalc in nm) of 6O from TD-CAM-B3LYP calculations using the CAM-B3LYP geometries at both S0-state and the S1-state optimized geometries in THF 143
   Table 3-17. Molecular orbital distributions (in %) and energies (in eV) of 6O at both S0-state and the S1-state fully optimized geometries in THF 144
   Table 4-1. Photophysical data for αCB, βCB, and γCB 153
   Table 4-2. Crystallographic data and parameters for αCB and γCB 171
   Table 4-3. Selected angles (°) and bond lengths (Å) of αCB and γCB 172
   Table 4-4. Calculated oscillator strengths (fcalc) and absorption wavelengths (λcalc in nm) of αCB from TD-PBE0 calculations using the PBE0 geometries at both S0-state and the S1-state fully optimized geometries in THF 175
   Table 4-5. Molecular orbital distributions (in %) and energies (in eV) of αCB at both S0-state and the S1-state fully optimized geometries in THF 176
   Table 4-6. Calculated oscillator strengths (fcalc) and absorption wavelengths (λcalc in nm) of βCB from TD-PBE0 calculations using the PBE0 geometries at both S0-state and the S1-state fully optimized geometries in THF 178
   Table 4-7. Molecular orbital distributions (in %) and energies (in eV) of βCB at both S0-state and the S1-state fully optimized geometries in THF 179
   Table 4-8. Calculated oscillator strengths (fcalc) and absorption wavelengths (λcalc in nm) of γCB from TD-PBE0 calculations using the PBE0 geometries at both S0-state and the S1-state fully optimized geometries in THF 181
   Table 4-9. Molecular orbital distributions (in %) and energies (in eV) of γCB at both S0-state and the S1-state fully optimized geometries in THF 182
   Table 4-10. Calculated oscillator strengths (fcalc) and absorption wavelengths (λcalc in nm) of αCB·(CHCl3)2 from TD-PBE0 calculations using the PBE0 geometries at both S0-state and the S1-state fully optimized geometries in THF 184
   Table 4-11. Molecular orbital distributions (in %) and energies (in eV) of αCB·(CHCl3)2 at both S0-state and the S1-state fully optimized geometries in THF 184
   Figure List
   Figure 1-1. The structures of ortho-, meta-, para-carborane 1
   Figure 1-2. Intramolecular Charge Transfer transition in D-A system with o-carborane 1
   Figure 1-3. Synthesis of 2,1,3-benzothiadiazole 2
   Figure 1-4. Luminescence mechanism of TADF 2
   Figure 1-5. Examples of TADF emitters 3
   Figure 2-1. Molecular orbitals participating in the absorption and emission processes for geometries of model compound 1-[C6H4(NH)2B]-1,2-C2B10H11 with ψ = 0° and ψ = 90° 7
   Figure 2-2. a) PL spectra of PCZ-CB-TRZ in THF/H2O mixtures with different water fractions (fw). b) Plots of absolute PL quantum yields (ФPL) versus fw of the aqueous mixtures. Inset in (b): fluorescence images of PCZ-CB-TRZ in pure THF (fw = 0%) and in a THF/H2O mixture (fw = 90%) under UV light irradiation. c) Streak image and prompt and delayed emission spectra (left) and transient PL decay profile (right) of a neat film of PCZ-CB-TRZ obtained at 300 K (inset: photograph of yellow PL from the neat film). Green dots in the streak image in (c) represent PL photon counts 7
   Figure 2-3. Synthetic pathways of the fluorene-based o-carboranyl luminophores. Reagents and conditions: (ⅰ) Phenylacetylene, Pd(PPh3)2Cl2, CuI, NEt3/toluene, 110 °C, 24 h. (ⅱ) Trimethylsilyl acetylene, Pd(PPh3)2Cl2, CuI, NEt3/toluene, 110 °C, 24 h. (ⅲ) K2CO3, MeOH/DCM, 25 °C, 2 h. (ⅳ) B10H14, Et2S, toluene, 120 °C, 24 h. (ⅴ) Tetra-n-butylammonium fluoride (TBAF), THF, 60 °C, 24 h. The single crystal structures for (b) 2FC, (c) 3FC, (d) 4FC, and (e) 4FCH (Solvent molecules in the unit cell, hydrogen atoms, and 50% thermal ellipsoids were excluded for clarity.) 9
   Figure 2-4. Molecular structure of 4FC exhibiting distorted fluorene plane formation 10
   Figure 2-5. UV-vis absorption (left side) and photoluminescence spectra (right side) of (a) 2FC (λex = 307 nm), (b) 3FC (λex = 300 nm), (c) 4FC and nido-4FC (λex = 318 nm), (d) 4FCH (λex = 309 nm). The inset figures depict the emission color in each state when exposed to illumination from a handheld UV lamp (λex = 265 nm) 11
   Figure 2-6. UV-vis absorption and PL spectra for 9,9-dimethyl-9H-fluorene (λex = 302 nm) in THF (3.0 × 10–5 M) 12
   Figure 2-7. The frontier molecular orbitals for 2FC, 3FC, and 4FC at both their S0- and S1-states, along with their relative energies from DFT calculation (isovalue 0.04), were determined. Transition energies (in nm) were calculated using the TD-B3LYP method with 6-31G(d) basis sets 13
   Figure 2-8. PL spectra of (a) 4FC (λex = 318 nm) and (b) 4FCH (λex = 309 nm) in various organic solvents (3.0 × 10–5 M) 14
   Figure 2-9. PL spectra of (a) 2FC, (b) 3FC, and (c) 4FC in THF/distilled water mixtures (3.0 × 10−5 M, λex = 307 nm for 2FC, 300 nm for 3FC and 318 nm for 4FC). The inset figures depict the emission color in each state when exposed to illumination from a handheld UV lamp (λex = 265 nm) 16
   Figure 2-10. Raman spectra of 2FC, 3FC, and 4FC (Laser: 633 nm (He-Ne laser), Exposure time: 3 s, Object: ×100 vis, Power: 0.3 mW) 17
   Figure 2-11. Emission decay curves for 4FC:(a) In THF (3.0 × 10–5 M) detected at 628 nm at 298 K. (b) In the film state (5 wt% doped in PMMA) detected at 574 nm at 298 K. Each red line represents its double exponential fitting curve 18
   Figure 2-12. Emission decay curves for (a) 2FC, (b) 3FC, and (c) 4FCH in the film state (5 wt% doped in PMMA) detected at each CT based emission maxima at both 298 K (black-line) and 77 K (green-line). Each red-line is its single exponential fitting curve for the decay curves at 298 K 19
   Figure 2-13. The relative energy diagrams for each S0, S1, and T1 states: (a) 2FC, (b) 3FC, (c) 4FC, and (d) 4FCH with varying dihedral angle (Ψ). Each purple line represents the energy gaps between the relative energy levels of the S1 and T1 states 20
   Figure 2-14. PL spectra of 4FC (λex = 318 nm) in oxygen-free and aerated THF (3.0 × 10−5 M) at 298 K 21
   Figure 2-15. Fluorescent (green solid line, prompt PL) and phosphorescent (purple solid line, 100 ns delayed PL) spectra of 4FC in THF at 77 K (3.0 × 10−5 M, λex = 318 nm) 23
   Figure 2-16. Arrhenius plots of the RISC rate constant (kRISC) of 4FC (a) in THF and (b) film state. ΔEST of each state was determined from least-squares fitting 23
   Figure 2-17. (a) Cyclic voltammograms for 2FC, 3FC, and 4FC, illustrating oxidation (pink solid line) and reduction (navy) potentials (5.0 × 10−4 M DCM solution, scan rate = 0.1 V/s). (b) TGA and (c) DSC curves for 2FC, 3FC, and 4FC 25
   Figure 2-18. Cyclic voltammograms of (a) 2FC, (b) 3FC, and (c) 4FC showing oxidation and reduction on consecutive five-time cycles (5.0 × 10−4 M DCM solution, scan rate = 0.1 V/s) 25
   Figure 2-19. 1H (top) and 13C (bottom) NMR spectra of 2FA (* from residual CH2Cl2 in CD2Cl2) 36
   Figure 2-20. 1H (top) and 13C (bottom) NMR spectra of 3FA (* from residual CH2Cl2 in CD2Cl2) 37
   Figure 2-21. 1H (top) and 13C (bottom) NMR spectra of 4FA (* from residual CH2Cl2 in CD2Cl2) 38
   Figure 2-22. 1H (top) and 13C (bottom) NMR spectra of 4FASi (* from residual CH2Cl2 in CD2Cl2) 39
   Figure 2-23. 1H (top) and 13C (bottom) NMR spectra of 4FAH (* from residual CH2Cl2 in CD2Cl2) 40
   Figure 2-24. 1H{11B} (top) and 13C (bottom) NMR spectra of 2FC (* from residual CH2Cl2 in CD2Cl2) 41
   Figure 2-25. 11B{1H} NMR spectra of 2FC in CD2Cl2 42
   Figure 2-26. 1H{11B} (top) and 13C (bottom) NMR spectra of 3FC (* from residual CH2Cl2 in CD2Cl2) 43
   Figure 2-27. 11B{1H} NMR spectra of 3FC in CD2Cl2 44
   Figure 2-28. 1H{11B} (top) and 13C (bottom) NMR spectra of 4FC (* from residual CH2Cl2 in CD2Cl2) 45
   Figure 2-29. 11B{1H} NMR spectra of 4FC in CD2Cl2 46
   Figure 2-30. 1H{11B} (top) and 13C (bottom) NMR spectra of 4FCH (* from residual CH2Cl2 in CD2Cl2) 47
   Figure 2-31. 11B{1H} NMR spectra of 4FCH in CD2Cl2 48
   Figure 2-32. 1H{11B} (top) and 13C (bottom) NMR spectra of nido-4FC (* from residual CH2Cl2 in CD2Cl2) 49
   Figure 2-33. 11B{1H} NMR spectra of nido-4FC in CD2Cl2 50
   Figure 2-34. The selected frontier orbitals of 2FC from PBE0 calculations (Isovalue = 0.04 a.u.) at both S0-state and the S1-state fully optimized geometries in THF 55
   Figure 2-35. The selected frontier orbitals of 3FC from PBE0 calculations (Isovalue = 0.04 a.u.) at both S0-state and the S1-state fully optimized geometries in THF 58
   Figure 2-36. The selected frontier orbitals of 4FC from PBE0 calculations (Isovalue = 0.04 a.u.) at both S0-state and the S1-state fully optimized geometries in THF 61
   Figure 3-1. Carbazole-based o-carboranyl luminophores 69
   Figure 3-2. Synthetic route for fabricating functionalized-biphenyl-based o-carboranyl compounds (1T‒6O). Reagents and conditions: (a) Pd(PPh3)2Cl2, CuI, trimethylsilyl acetylene, toluene/NEt3 (3/2, v/v), 90 °C, 24 h; (b) K2CO3, MeOH, rt, 2 h; (c) B10H14, Et2S, 120 °C, 24 h; (d) n-BuLi (for 1T, 2F, 3H, 4M, and 6O) or lithium di-isopropyl amide (for 5B), trimethylsilyl chloride, −78 °C, 10 min. Insets (dashed boxes) show the X-ray crystal structures of the o-carboranyl compounds (35% thermal ellipsoids); H atoms are omitted, and silylmethyl groups are represented as sticks for clarity (pink: boron, green: fluorine, and red: oxygen atoms) 70
   Figure 3-3. UV–vis absorption (left) and photoluminescence (PL) spectra (right) for (a) 1T (λex = 284 nm), (b) 2F (λex = 289 nm), (c) 3H (λex = 288 nm), (d) 4M (λex = 297 nm), (e) 5B (λex = 297 nm), and (f) 6O (λex = 309 nm). The inset figures depict the emission color in each state when exposed to illumination from a handheld UV lamp (λex = 265 nm); those for 1T‒3H could not be obtained due to the weak emissive trace 73
   Figure 3-4. Frontier molecular orbitals for functionalized-biphenyl-based o-carboranyl compounds 1T‒6O in the S0- and S1-states showing the relative energies obtained using density functional theory calculations (isovalue 0.04). The transition energy (in nm) was computed using the TD-CAM-B3LYP/6-31G(d,p) level of theory 75
   Figure 3-5. Emission decay curves for (a) 2F, (b) 3H, (c) 4M, (d) 5B, and (e) 6O in the film state detected at each emissive maxima at 298 K. Each green-line is its single or double exponential fitting curve for the decay curves 77
   Figure 3-6. PL spectra of (a) 4M (λex = 297 nm), (b) 5B (λex = 297 nm), and (c) 6O (λex = 309 nm) in THF/distilled water mixtures (5.0 × 10−5 M). The inset figures depict the emission color in each state when exposed to illumination from a handheld UV lamp (λex = 265 nm); those for 4M and 5B could not be obtained due to the weak emissive trace 78
   Figure 3-7. Calculated atomic charge for 1T‒6O at the S1-optimised geometry in THF with the dipole moment (μ) values. The size and direction of blue arrow indicate those for each the dipole moments, respectively 78
   Figure 3-8. 1H (top) and 13C (bottom) NMR spectra of 1TA in CDCl3 (* from residual CHCl3 in CDCl3) 93
   Figure 3-9. 1H (top) and 13C (bottom) NMR spectra of 2FA in CDCl3 (* from residual CHCl3 in CDCl3) 94
   Figure 3-10. 1H (top) and 13C (bottom) NMR spectra of 3HA in CDCl3 (* from residual CHCl3 in CDCl3) 95
   Figure 3-11. 1H (top) and 13C (bottom) NMR spectra of 4MA in CD2Cl2 (* from residual CH2Cl2 in CD2Cl2) 96
   Figure 3-12. 1H (top) and 13C (bottom) NMR spectra of 5BA in CDCl3 (* from residual CHCl3 in CDCl3) 97
   Figure 3-13. 1H (top) and 13C (bottom) NMR spectra of 6OA in CDCl3 (* from residual CHCl3 in CDCl3) 98
   Figure 3-14. 1H{11B} (top) and 13C (bottom) NMR spectra of 1TH in CDCl3 (* from residual CHCl3 in CDCl3) 99
   Figure 3-15. 11B{1H} NMR spectra of 1TH in CDCl3 100
   Figure 3-16. 1H{11B} (top) and 13C (bottom) NMR spectra of 2FH in CDCl3 (* from residual CHCl3 in CDCl3) 101
   Figure 3-17. 11B{1H} NMR spectra of 2FH in CDCl3 102
   Figure 3-18. 1H{11B} (top) and 13C (bottom) NMR spectra of 3HH in CDCl3 (* from residual CHCl3 in CDCl3) 103
   Figure 3-19. 11B{1H} NMR spectra of 3HH in CDCl3 104
   Figure 3-20. 1H{11B} (top) and 13C (bottom) NMR spectra of 4MH in CD2Cl2 (* from residual CH2Cl2 in CD2Cl2) 105
   Figure 3-21. 11B{1H} NMR spectra of 4MH in CD2Cl2 106
   Figure 3-22. 1H{11B} (top) and 13C (bottom) NMR spectra of 5BH in CDCl3 (* from residual CHCl3 in CDCl3) 107
   Figure 3-23. 11B{1H} NMR spectra of 5BH in CDCl3 108
   Figure 3-24. 1H{11B} (top) and 13C (bottom) NMR spectra of 6OH in CDCl3 (* from residual CHCl3 in CDCl3) 109
   Figure 3-25. 11B{1H} NMR spectra of 6OH in CDCl3 110
   Figure 3-26. 1H{11B} (top) and 13C (bottom) NMR spectra of 1T in CDCl3 (* from residual CHCl3 in CDCl3) 111
   Figure 3-27. 11B{1H} (top) and 19F (bottom) NMR spectra of 1T in CDCl3 112
   Figure 3-28. 1H{11B} (top) and 13C (bottom) NMR spectra of 2F in CDCl3 (* from residual CHCl3 in CDCl3) 113
   Figure 3-29. 11B{1H} (top) and 19F (bottom) NMR spectra of 2F in CDCl3 114
   Figure 3-30. 1H{11B} (top) and 13C (bottom) NMR spectra of 3H in CDCl3 (* from residual CHCl3 in CDCl3) 115
   Figure 3-31. 11B{1H} NMR spectra of 3H in CDCl3 116
   Figure 3-32. 1H{11B} (top) and 13C (bottom) NMR spectra of 4M in CD2Cl2 (* from residual CH2Cl2 in CD2Cl2) 117
   Figure 3-33. 11B{1H} NMR spectra of 4M in CD2Cl2 118
   Figure 3-34. 1H{11B} (top) and 13C (bottom) NMR spectra of 5B in CDCl3 (* from residual CHCl3 in CDCl3) 119
   Figure 3-35. 11B{1H} NMR spectra of 5B in CDCl3 120
   Figure 3-36. 1H{11B} (top) and 13C (bottom) NMR spectra of 6O in CDCl3 (* from residual CHCl3 in CDCl3) 121
   Figure 3-37. 11B{1H} NMR spectra of 6O in CDCl3 122
   Figure 3-38. The selected frontier orbitals of 1T from CAM-B3LYP/6-31G(d,p) calculations (Isovalue = 0.02 a.u.) at the S0- and the S1-optimized geometries in THF 127
   Figure 3-39. The selected frontier orbitals of 2F from CAM-B3LYP/6-31G(d,p) calculations (Isovalue = 0.02 a.u.) at the S0- and the S1-optimized geometries in THF 130
   Figure 3-40. The selected frontier orbitals of 3H from CAM-B3LYP/6-31G(d,p) calculations (Isovalue = 0.02 a.u.) at the S0- and the S1-optimized optimized geometries in THF 133
   Figure 3-41. The selected frontier orbitals of 4M from CAM-B3LYP/6-31G(d,p) calculations (Isovalue = 0.02 a.u.) at the S0- and the S1-optimized optimized geometries in THF 136
   Figure 3-42. The selected frontier orbitals of 5B from CAM-B3LYP/6-31G(d,p) calculations (Isovalue = 0.02 a.u.) at the S0- and the S1-optimized optimized geometries in THF 139
   Figure 3-43. The selected frontier orbitals of 6O from CAM-B3LYP/6-31G(d,p) calculations (Isovalue = 0.02 a.u.) at the S0- and the S1-optimized geometries in THF 142
   Figure 4-1. Organic fluorophores based on 2,1,3-benzothiadiazole derivatives with a carbazole moiety 150
   Figure 4-2. A red TADF emitter with a benzothiadiazole-based D-A-D structure led to high-performance OLEDs, achieving a maximum EQE of 8.8% and CIE coordinates of (0.61, 0.39) 150
   Figure 4-3. Thermochromic phenomenon of 2,1,3-benzothiadiazole-based D–A–D-type organic luminophores 151
   Figure 4-4. (a) Synthesis of the carboline-based benzothiadiazole compounds αCB, βCB, and γCB. Reaction conditions: (i) CuI, K3PO4, (±)-trans-1,2-diaminocyclohexane, toluene, 150 °C, 48 h. (b, c) X-ray crystal structures of (b) αCB and (c) γCB (40% thermal ellipsoids), with H atoms and solvents in the unit cell omitted for clarity 152
   Figure 4-5. UV-vis absorption (left side) and PL (right side) spectra of (a) αCB (λex = 412 nm), (b) βCB (λex = 420 nm), and (c) γCB (λex = 419 nm). The inset figures depict the emission color in each state when exposed to illumination from a handheld UV lamp (λex = 365 nm) 153
   Figure 4-6. UV-Vis absorption of α-, β-, and γ-carboline in THF (5.0 × 10−5 M) at 298 K 154
   Figure 4-7. UV-Vis absorption and PL spectra of (a) αCB, (b) βCB, and (c) γCB in various organic solvents (5.0 × 10−5 M) 154
   Figure 4-8. Plots of Stokes shift for (a) αCB, (b) βCB, and (c) γCB as a function of relative solvent polarity parameters 155
   Figure 4-9. Frontier molecular orbitals of αCB, βCB, and γCB in their S0-states and the S1-states and their relative energies obtained from the DFT calculations (isovalue = 0.04). Transition energies (in nm) were calculated using the TD-PBE0 method with the 6-31G(d,p) basis set 156
   Figure 4-10. Excitation graphs of αCB, βCB, and γCB in THF (5.0 × 10−5 M) 157
   Figure 4-11. Emission decay curves for (a) αCB, (b) βCB, and (c) γCB in THF (5.0 × 10−5 M) were recorded at their respective ICT-based emission maxima at 298 K. Each red line represents the single-exponential fitting curve for the decay curves 158
   Figure 4-12. Emission decay curves for (a) αCB, (b) βCB, and (c) γCB in the film state (5 wt% doped in PMMA) were recorded at their respective ICT-based emission maxima at 298 K. Each red line represents the single-exponential fitting curve for the decay curves 158
   Figure 4-13. Intermolecular interactions in a unit cell of crystalline αCB (red line: a-axis, green line: b-axis, and blue line: c-axis; green ball: chlorine atom and white ball: hydrogen atom) 159
   Figure 4-14. Emission spectra of (a) αCB, (b) βCB, and (c) γCB in the solid crystalline and ground states and after treatment with CHCl3 at 298 K. The inset figures depict the emission color in each state when exposed to illumination from a handheld UV lamp (λex = 365 nm). (d) Repeat experiments of the mechanofluorochromic behaviors of αCB, βCB, and γCB 160
   Figure 4-15. (a) Emissive spectra of crystalline and heated solid state to 50 °C, and after treating with chloroform (CHCl3) vapor for αCB. The inset figures depict the emission color in each state when exposed to illumination from a handheld UV lamp (λex = 365 nm). (b) Repetitive experiment of thermochromism for αCB 161
   Figure 4-16. Powder XRD patterns of αCB in the unground (crystalline), ground, and treated (with CHCl3 vapor) states 162
   Figure 4-17. Powder XRD patterns of (a) βCB and (b) γCB in the unground (crystalline), ground, and treated (with CHCl3 vapor) states 163
   Figure 4-18. 1H (top) and 13C (bottom) NMR spectra of αCB in CDCl3 (* from residual CHCl3 in CDCl3) 167
   Figure 4-19. 1H (top) and 13C (bottom) NMR spectra of βCB in CDCl3 (* from residual CHCl3 in CDCl3) 168
   Figure 4-20. 1H (top) and 13C (bottom) NMR spectra of γCB in CDCl3 (* from residual CHCl3 in CDCl3) 169
   Figure 4-21. The selected frontier orbitals of αCB from PBE0/6-31G(d,p) calculations (Isovalue = 0.04 a.u.) at the S0- and the S1-optimized geometries in THF 174
   Figure 4-22. The selected frontier orbitals of βCB from PBE0/6-31G(d,p) calculations (Isovalue = 0.04 a.u.) at the S0- and the S1-optimized geometries in THF 177
   Figure 4-23. The selected frontier orbitals of γCB from PBE0/6-31G(d,p) calculations (Isovalue = 0.04 a.u.) at the S0- and the S1-optimized geometries in THF 180
   Figure 4-24. The selected frontier orbitals of α-CB·2CHCl3 from PBE0 calculations (Isovalue = 0.02 a.u.) at both S0-state and the S1-state fully optimized geometries in crystalline 183
   Scheme List
   Scheme 2-1. Synthesis of 2FA 28
   Scheme 2-2. Synthesis of 3FA 28
   Scheme 2-3. Synthesis of 4FA 29
   Scheme 2-4. Synthesis of 4FASi 30
   Scheme 2-5. Synthesis of 4FAH 30
   Scheme 2-6. Synthesis of 2FC 31
   Scheme 2-7. Synthesis of 3FC 32
   Scheme 2-8. Synthesis of 4FC 33
   Scheme 2-9. Synthesis of 4FCH 33
   Scheme 2-10. Synthesis of nido-4FC 34
   Scheme 3-1. Synthesis of 1TA 81
   Scheme 3-2. Synthesis of 2FA 82
   Scheme 3-3. Synthesis of 3HA 82
   Scheme 3-4. Synthesis of 4MA 83
   Scheme 3-5. Synthesis of 5BA 83
   Scheme 3-6. Synthesis of 6OA 84
   Scheme 3-7. Synthesis of 1TH 85
   Scheme 3-8. Synthesis of 2FH 85
   Scheme 3-9. Synthesis of 3HH 86
   Scheme 3-10. Synthesis of 4MH 86
   Scheme 3-11. Synthesis of 5BH 87
   Scheme 3-12. Synthesis of 6OH 87
   Scheme 3-13. Synthesis of 1T 88
   Scheme 3-14. Synthesis of 2F 89
   Scheme 3-15. Synthesis of 3H 90
   Scheme 3-16. Synthesis of 4M 90
   Scheme 3-17. Synthesis of 5B 91
   Scheme 3-18. Synthesis of 6O 91
   Scheme 4-1. Synthesis of αCB 165
   Scheme 4-2. Synthesis of βCB 165
   Scheme 4-3. Synthesis of γCB 166