The considerably conjugated π systems of the group 14 dithienometallole-linked ethynylene-conjugated porphyrin dimers (1Ms) were described based on comprehensive experimental and theoretical studies. The electronic absorption spectra of 1M displayed a large splitting in the Soret band and a red-shifted Q-band, indicating that the dithienometallole spacer was effective in facilitating the porphyrin-porphyrin electronic coupling. Torsional planarization behaviors of 1M were observed in the time-resolved fluorescence spectra. Density functional theory (DFT) calculations revealed that the dithienometallole spacer is an ideal partner for the ethynylene-conjugated porphyrin to produce fully delocalized highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels due to their similar HOMO and LUMO levels. Finally, 1M exhibited a strong propensity for the quinoidal-cummulenic conjugation in the dithienometallole spacer when in a photoexcited state.