Poly(diiododiacetylene) (PIDA), formed by the topochemical polymerization of diiodobutadiyne within host-guest cocrystals, is a conjugated polymer containing an all-carbon backbone and only iodine atom substituents. Extensive rinsing and sonication of the PIDA cocrystals in organic solvents such as methanol, THF, and chloroform yield fibrous materials with diameters as low as 10-50 nm. Raman spectroscopy and C-13 MAS NMR confirm that these fibers contain PIDA but that the host has been removed. Polarized Raman scattering measurements indicate that the PIDA filaments are uniaxially oriented. The PIDA nanofibers are stable at room temperature when undisturbed but become explosive under external energy such as shock or pressure. They transform to sp(2)-hybridized carbon irreversibly at room temperature when irradiated with a 532 nm Raman laser beam. Under thermal conditions, the PIDA fibers start releasing iodine at 120 degrees C and undergo complete carbonization in 1 h by pyrolysis at 900 degrees C.