Emission spectra of single molecules of the conjugated polymer MEH-PPV in host matrices of ZEONEX (R) and polystyrene are reported. Depending on the matrix, the polymer chains attain different conformations, from compact defect cylinders to extended defect coils. The conformations are correlated with photophysical properties, such as emission intensity fluctuations, and with shapes and peaks of emission spectra. The observed bimodal distribution of the spectral peaks is related to distribution in conjugated segment lengths.