To gain insight into the length-dependent photophysical properties of AR-n and ARO-n, UV/Vis absorption and fluorescence emission were measured in diluted CH2Cl2 solutions at room temperature (Figure ). The results are summarized in Table . AR-17 (λabs = 434 nm, log ε = 5.24) exhibited a bathochromic shift compared to AR-11 (λabs = 415 nm, log ε = 5.07), which was attributed to the extended π-backbone. ARO-11 exhibited a pronounced bathochromic shift in its absorption maximum (λabs = 466 nm, log ε = 4.79) compared to AR-11 as well, attributable to the integration of the electron-withdrawing thiophene-S,Sdioxide unit into the extended π-system. Notably, ARO-11 displayed broader absorption features than AR-11. Similar trends were observed for ARO-17 and AR-17. Compared to AR-11 (λem = 459 nm), the bathochromic shift in the photoluminescence spectra was pronounced for AR-17 (λem = 479 nm) due to its extended conjugated backbone, or for ARO-11 (λem = 511 nm) due to incorporation of the electron-withdrawing thiophene-S,S-dioxide unit (Figure ). The absolute fluorescence quantum yields (ΦF) were measured by using an integrating sphere detector. In CH2Cl2 solution, ΦF values increased with π-backbone extension in AR-11 (15%) and AR-17 (37%). Conversely, ARO-11 (65%) and ARO-17 (71%) displayed high, πbackbone-independent ΦF values. In the solid state, however, ΦF values decreased to 5.9% for ARO-11 and 1.5% for ARO-17, likely due to aggregation-caused quenching via strong intermolecular π-overlap. Similar trends were observed for AR-11 (4.7%) and AR-17 (0.2%). To further elucidate the photophysical properties, the energy diagrams and frontier molecular orbitals of AR-n and AROn were calculated by the time-dependent density functional theory (TD-DFT) method at the PBE0-D3(BJ)/6-31G (d,p) level of theory (Figure and Figure -20). The lowest energy absorption bands of AR-n and ARO-n are attributed to the S0→S1 excitation (ΔE, 3.12 eV for AR-11, 2.74 eV for ARO-11, 2.97 eV for AR-17, 2.61 eV for ARO-17), which mainly arises from the HOMO→LUMO transition (95% for AR-11, 92% for ARO-11, 90% for AR-17, 87% for ARO-17) and has an oscillator strength (f) of 1.77 for AR-11, 1.19 for ARO-11, 3.07 for AR-17, and 2.11 for ARO-17 (Table ). The electrochemical properties of these GNRs were studied in THF solution by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). All compounds exhibited an obvious reduction process, with Ep red1 values of -1.51 eV (AR-11), -1.43 eV (ARO-11), -1.38 eV (AR-17), and -1.52 eV (ARO-17). Oxidation potentials (Ep ox1 ) were 0.93 eV (AR-11), 1.03 eV (ARO-11), 1.01 eV (AR-17), and 1.00 eV (ARO-17). Based on Ep ox1 values, HOMO energy levels were estimated as -5.07 eV (AR-11), -5.14 eV (ARO-11), -5.12 eV (AR-17), and -5.08 eV (ARO-17), demonstrating good agreement with the computational study (Figure , Scheme S5 and Table1). The energy levels of the calculated frontier molecular orbitals of AR-n and ARO-n are shown in Figure and Figure -20, for example, the HOMO and LUMO of AR-17 and ARO-17 spread over the whole π-system. After converting the electron-rich thiophene ring into an electron-poor thiophene-S,S-dioxides, the sulfone dioxide unit considerably reduces the HOMO orbital energy level; the LUMO orbital energy level has a greater decrease. Hence, the energy gap of the molecule is greatly reduced, which leads to a large redshift of fluorescence emission. Notably, the band gaps of AR-n and ARO-n are well regulated from 3.90 eV of AR-5 to 3.11 eV of AR-23 and 3.43 eV of ARO-5 to 2.81 eV of ARO-23. The energies of frontier orbitals of AR-n and ARO-n are plotted in Figure (also see Figure ). The decrement of the LUMO energy level and increment of the HOMO energy level are observed from AR-5 to AR-23, which leads to a clear shrinkage of Eg in the same sequence. The decreased HOMO level for ARO-n compared with AR-n strongly suggests the enhanced affinity of ARO-n to electrons.