Incorporation of duplex DNA with higher molecular weights has attracted attention for a new opportunity towards a better organic light-emitting diode (OLED) capability. However, biological recognition by OLED materials is yet to be addressed. In this study, specific oligomeric DNA？DNA recognition is successfully achieved by tri (8-hydroxyquinoline) aluminium (Alq₃), an organic semiconductor. Alq₃ rods crystallized with guidance from single-strand DNA molecules show, strikingly, a unique distribution of the DNA molecules with a shape of an ‘inverted’ hourglass. The crystal’s luminescent intensity is enhanced by 1.6-fold upon recognition of the perfect-matched target DNA sequence, but not in the case of a single-base mismatched one. The DNA？DNA recognition forming double-helix structure is identified to occur only in the rod’s outer periphery. This study opens up new opportunities of Alq₃, one of the most widely used OLED materials, enabling biological recognition.