Detailed absorption and emission behavior were investigated for a sexthiophene molecule in solution, film, and solid. Only strong polarity solvent could result a notable influence on the quench of its fluorescence. In weak and medium polar environment, including in polymer matrix, highly emissive behavior was maintained and exhibit large Stokes shift. More important is its highly emissive in solid state due to the twisted molecular conformation. However, the bandwidth of solid emission (FWHM: 2149 cm(-1)) is similar to that of solution emission. The calculated frontier orbital based on TDDFT theory uncovered the underlying signal mechanism furtherly.