To further examine the size-dependent characteristics of 5T, 6T, and reference compound 4T, their UV/vis absorption spectra were recorded (Fig. ). The maximum absorption for all three compounds was observed at ~230 nm, and the longestwavelength absorption maxima were observed at 263, 273, and 276 nm for 4T, 5T, and 6T, respectively. The frontier molecular orbitals related to the longest absorption bands and their energy levels are depicted in Fig. , taking into account the vertical excitation energies, oscillator strengths, and transition contributions obtained from time-dependent (TD) DFT calculations (see Fig. in ESI for details). Because 4T adopts a highly symmetrical structure, the electronic wavefunctions of the HOMO and LUMO are distributed over the entire molecule, and the HOMO and the HOMO-1 are degenerate. In contrast, the HOMO and LUMO of 5T and 6T are relatively localized, presumably because of their lower-symmetry structures. The shoulder peaks in the range of 260-280 nm can be attributed to a combination of the HOMO-1→LUMO and HOMO→LUMO transitions for 4T, and the HOMO→LUMO transitions for 5T and 6T. With increasing number of thiophene rings, the HOMO level rises gradually from -6.09 eV to -5.76 eV, while the LUMO energy decreases from 4T to 5T and is similar for 5T and 6T.