The photoisomerization behavior of benzylideneacetophenones, known as chalcones, was studied.
We synthesized the chalcone derivatives that have ether groups at 4 and 4’ positions.
Due to the electron donating ability of the ether oxygen, the bond order of the single bond between two phenyl ring of the chalcone strengthened, which eventually increased the rotational barrier of the single bond.
The rotational barrier of the single bond is about 20-22 kcal/mole.
Thermal recovery of this process took about 1 min.
The UV-visible spectra of these chromophores exhibit two characteristic absorption peaks at 276 nm and 340 nm.
The relative intensity of the peaks varies depending on the alkyl chain length of the substituent.
Photo-irradiation with the 365 nm light monotonously decreases the 340 nm peak.
However, the photo-irradiation with 254 nm light induce two competing processes and produced rather complicated absorption profile.