Highly monodisperse block copolymers allow for the preparation of luminescent particles with sizes reflecting the oligomer chain length. Self-organization in tetrahydrofuran/methanol leads to anisotropic nanorods with a thickness corresponding directly to the oligomer length (up to 14 nm for 21-mers). As a prerequisite for the realization of this concept, syntheses of defect-free poly(phenylene ethynylene)s with unprecedented chain length up to 43 repeat units were developed. Absorption and emission wavelength in solution continue to increase with increasing chain length, and do not converge until the 43-mer.