Proton Activated Photoisomerization of Dibenzofulvene Molecular Actuators
AuthorJayasundara, Udaya Kumara
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Our group has shown that dibenzofulvene rotors behave as an efficient class of light driven molecular actuators that give a range of photoisomerization quantum yields from 0.04 to 0.5 depend upon the substituents. This work shows the protonation dependence in photoisomerization quantum yields for amino and dimethylamino substituted dibenzofulvene derivatives. Both rotors were protonated with trifluoroacetic acid (TFA) and triflic acid (TfOH) and it was discovered that TfOH gives the highest quantum yield in all cases. In contrast, addition of triethlyamine (TEA) base does not significantlychange quantum yields regardless of the amount added. This behavior could be due to the change in the electron densities with protonation and deprotonation, which could be explained by the electron donating/withdrawing character of each substituent. Photoisomerization was conducted at 266 and 310 nm and was monitored by gas and liquid chromatography and by <super>1</super> H NMR. The protonation dependence is found only in amino (ATEF) and dimethylamino (DTEF) compounds. For other substituents, such as nitro and cyano, changes in protonation do not significantly affect the quantum yields. In addition, computational calculations were performed on the rotor parts of these motor prototypes.