Irradiation Specified Conformational Change in a Small Organic Compound and Its Effect on Electrical Properties

The simple and small organic compound bis((quinolin-4-yl)methylene)benzene-1,4-diamine (BQD) has been synthesized by a one-step Schiff-base condensation reaction, and it has been characterized by elemental analysis, some standard spectroscopic methods, and the X-ray single crystal diffraction technique. It shows the unique property of photosensitivity with about 10 times increase in electrical conduction under irradiation of visible light of a specific wavelength (700 nm), in comparison to dark conditions. However, UV light (350 nm) or visible light of different wavelength (500 or 600 nm) cannot cause an enhancement in its electrical conduction. The electric current measurement of BQD exhibits its response ability toward visible light but not to UV illumination when current is measured several times under a constant bias voltage by putting light on and off with successive repetitions. Theoretical calculations indicate that a slight conformational change in the C═N bond and dihedral angle leading to the increase in planarity in the molecule caused under visible light of a specific wavelength (700 nm) is responsible for its photosensitivity and electrical conductivity. A new molecule (Me 2 -BQD) with two methyl groups in the central phenyl ring shows lower conductivity in comparison to BQD under visible (700 nm), UV (350 nm) light, and dark conditions.