Vertical organic nanowire arrays of 1,5-diaminoanthraquinone (DAAQ) on solid substrates were prepared by a facile physical vapor transport method. The crystal structure and growth direction of the nanowires were determined with electron diffraction. The color and fluorescence of the DAAQ nanowires can be bleached and quenched by acid vapor and rapidly regenerated by base vapor, making them useful as optical sensor materials. The ease of oriented vertical growth makes them promising nanophotonic elements that may be directly integrated into photonic devices during growth.