An ABA triblock conjugated copolymer, poly(2,5-benzoxazole)-block-poly(benzobisthiazole-2,6-diyl-1,4-phenylene)-block-poly(2,5-benzoxazole), 1, was synthesized, characterized, and used to demonstrate spatial confinement effects on the electronic structure and the optical and optoelectronic properties of block copolymers. Optical absorption, photoluminescence, and photoluminescence excitation spectra of thin films of the triblock copolymer evidence spatial confinement of excitons as well as microphase separation. Efficient energy transfer via interchain and intrachain mechanisms was observed in the triblock conjugated copolymer. The results suggest that microphase separation in hulk block conjugated copolymers can significantly modify the spatial modulation and confinement dimensionalities expected in isolated block copolymer chains.