We have developed a dark-field optical microspectrscopic system coupled with AFM measurement, and applied it to 1, 6-di(N-carbazolyl)-2-4-hexadiyne (DCHD) nanocrystal systems. We revealed clearly the size and shape dependent peak of the polymer-backbone electronic transition of individual poly-DCHD nanocrystals. It was found that the peak energy of the resonant Rayleigh scattering spectra shifted to a lower energy for nanocrystals having larger cross-section against its long axis. In situ observation of photopolymerization of individual monomer DCHD nanocrystals is also descried. It has been successfully demonstrated that the morphological of fibrous nanocrystal changes upon polymerization. Our single particle results demonstrate that far-field microscopy coupled with AFM is a reliable experimental approach for investigating optical properties and photochemistry of organic nanoparticles.