The synthesis of a unique type of π-expanded coumarin derivatives, bearing six fused phenyl rings, was achieved via one-pot Suzuki reaction and visible light-driven electrocyclization. The large π-expanded 5H-benzo[12,1]tetrapheno[7,6,5-cde]chromen-5-ones were obtained in good to high yields from 1-bromo-2H-phenaleno[1,2,3-de]chromen-2-ones, and the intriguing optical properties were explored by altering the attached functional groups. 2-Arylaminosubstituted-5H-benzo[12,1]tetrapheno[7,6,5-cde]chromen-5-ones showed a large Stokes shift (4005 cm-1) or excellent fluorescence quantum yield (Φf = 0.75) along with significant bathochromic shift in tetrahydrofuran.