Confocal Raman spectroscopy was employed to investigate the photoisomerization of Cn HAT powders. To get information about the expected changes in the Raman spectra of Cn HATs upon photoisomerization, density functional theory (DFT) calculations with the B3LYP method using a basis set of 6-31G were performed to simulate the vibrational spectra of the Z and E isomers of Cn HAT (Figure ). We found that all the Raman spectra of the Z and E isomers of Cn HAT molecules show similar features. In the spectrum of Z isomers, the peaks at 990 and 1618 cm -1 correspond to the breathing and stretching modes of the benzene rings, respectively. Both peaks remain the same after Z-to-E isomerization. Upon the Z-to-E isomerization, the peaks at 1436 and 1475 cm -1 , which are associated with the C=N stretching mode, shift to 1565 cm -1 . Additionally, the peak corresponding to the C=O stretching mode shifts from 1670 cm - 1 to 1737 cm -1 , which is attributed to the disappearance of the intramolecular hydrogen bonding between the carbonyl oxygen of the ester and the nitrogen of the aniline. Moreover, the intensity of the peak at 1024 cm -1 (the C-H bending mode) increases and the C-N stretching mode slightly shifts from 1508 cm -1 to 1524 cm -1 . The peaks at 1576 and 1737 cm -1 are characteristic peaks of the E isomer and the peaks at 1435, 1476, and 1670 cm -1 are the characteristic peaks of the Z isomer. It is noteworthy that because of the small Raman cross-section of the C=O bond, this vibrational mode is usually very weak in Raman spectra. Hence, the decrease of the peaks at 1435 and 1475 cm -1 , and the new peak appearing at 1565 cm -1 were used to determine the Z-to-E isomerization of the molecules.