The experimental Raman spectra of Cn HAT powder samples before and after irradiation at 415 nm or 340 nm were collected and are shown in Figure . Before light irradiation, all the Raman spectra (black curves in Figure ) of Cn HAT powders show similar features and are in good agreement with the simulated spectrum of the Z isomer. After irradiation with 415 nm light, we observed similar changes in the Raman spectra in all cases, but to various extents for the different compounds. For C3 HAT (Figure ), a slight decrease in intensity of the peaks at 1436 and 1476 cm -1 and a new peak appearing at 1565 cm -1 were observed. Moreover, the peak intensity at 1680 cm -1 decreases while a new peak appears at 1709 cm -1 (red curve shown in the insets). All these changes are consistent with the results of the predicted Raman spectra, suggesting that some of the Z-C3 HAT molecules have isomerized to the E form. For C8 HAT, C10 HAT, and C11 HAT (Figure ), the peak intensity at 1436 cm -1 significantly decreased and the peak at 1475 cm -1 almost disappears, while a prominent peak appears at 1709 cm -1 . Additionally, the peak at 1680 cm -1 completely shifts to 1709 cm -1 (the red curves shown in the insets). Such changes indicate a very high photoconversion efficiency. As described above, the peaks at 1680 and 1709 cm -1 only refer to the C=O vibrational mode, and thus the ratio of these two peaks can be used to estimate the PSS. A Gaussian fit was performed to calculate the ratio of the two isomers (Figure ). For C3 HAT, the E and Z ratio at PSS 415 is calculated to be 48:52, which is much smaller than that in the solution phase. For C8, C10, and C11 HAT, this ratio is 97:3, 92:8, and 97:3 (see Table ), respectively. The switching efficiency of these compounds is comparable to our earlier results reported for C6 HAT powders. The lower conversion efficiency of C3 HAT powders upon 415 nm light irradiation is likely because of the strong intermolecular interactions of C3 HAT. The molecular volume of C3 HAT is smaller than that of other Cn HAT (n = 8, 10, 11) molecules, and hence, we speculate that the hydrazone skeleton of C3 HAT is more closely packed in the bulk material, i.e., there is less free volume for C3 HAT to accommodate the change in shape upon isomerization, and stronger steric effects among molecules, compared with other Cn HAT molecules.