The time-resolved photoluminescence of cyclodextrin-threaded conjugated molecular wires and their unthreaded analogues is studied to probe suppression of intermolecular interactions by supramolecular encapsulation. The polyrotaxane dynamics are exponential and independent of concentration, different from those of unthreaded semiconductors, which display instead optical signatures of interchain species. This is fundamental insight into the photophysics of semiconducting polymers, and crucial for the development of organic electronics.