New π-conjugated 1,2-bis(2-aryl-1H-indol-3-yl)ethynes 1a-j having various substituents on the two aryl groups were efficiently synthesized via unusual 5-exo-digonal double isocyanide-acetylene cyclization reactions of 1,4-bis(2-isocyanophenyl)buta-1,3-diyne 3 and aryl Grignard reagents (R-MgBr, R = CH (1a), 4-HCCH (1b), 2-HCCH (1c), 3-MeOCH (1d), 3-(CH)NCH (1e), 4-FCCH (1f), 4-FCH (1g), 3-FCH (1h), 4-PhOCH (1i), and 2-Naph (1j)) in 19-85% yields. The UV-vis spectra were rationalized in detail using time-dependent DFT and single point calculations. The fluorescence emission peaks for 1a-j were observed at around 450 nm. Especially for 1f and 1j, those spectra displayed broad emission bands and relatively large Stokes shifts (3977-4503 cm), indicating the contribution of an intramolecular charge transfer. The absolute quantum yields (0.50-0.62) of 1a-j were higher than those of parent 8 (0.19) and 2-phenyl-1H-indole (0.11). The electrochemical features for 1a-j were investigated by cyclic voltammetry. The frontier molecular orbital levels for 1a-j were estimated based on the combination of oxidation potentials, UV-vis, and DFT calculated data. The structural property of 1,2-bis(2-phenyl-1H-indol-3-yl)ethyne 1a was characterized by several spectroscopic methods and finally determined by X-ray analysis of a single crystal of 1a recrystallized from ethyl acetate. The structural features of 1a-j were also supported by DFT calculations.

A series of six new ethynylene‐bridged conjugate carbazole trimers (1–6) were synthesized through sequential Pd‐catalyzed Sonogashira cross‐coupling reactions. The structural properties of these trimers were examined by using DFT calculations. Compound 6, in which the two terminal carbazole moieties were substituted at the 1‐position, exhibited the longest‐wavelength UV/Vis absorption maximum in CH2Cl2, whereas compound 1, in which the two terminal carbazole moieties were substituted at the 3‐position, exhibited the shortest‐wavelength absorption maximum. These trends were rationalized by using TDDFT calculations. Electrochemical measurements and DFT calculations revealed that trimers 1–6 had smaller HOMO–LUMO gaps compared with that for the corresponding monomer (14), which was caused by a lowering of the LUMO levels, rather than by a raising of the HOMO levels. Trimers 2–6 exhibited excellent emission properties with high fluorescence quantum yields, which were derived from their rigid structures.