Elucidation of Photoisomerization-Related Structural Changes in an Acrylamide-Bridged Binaphthalene–Diazene Macrocyclic Chiroptical Switch by Experimental Electronic Circular Dichroism Spectra Simulation: Role of Dispersion Corrections

Nondestructive readout of light-driven molecular memory devices can be achieved by monitoring the alterations in the chiroptical properties of 1,1′-binaphthalene as a conformationally responsive chiral group. In our system, this signaling unit is connected via acrylamide linkers to the receiving diphenyldiazene fragment, which undergoes significant geometrical changes upon (<i>E</i>)/(<i>Z</i>)-photoisomerization. The compound functions as a stable photochromic switch by alternating irradiation at 365/465 nm, with fully reversible modulation of circular dichroism (CD) signal intensity (up to 1:3) and extended thermal stability of the (<i>Z</i>)-isomer. According to molecular modeling, the acrylamide spacers are due to the imposed cyclic strain upon photoisomerization forced to switch amide conformations, which is markedly reflected in the CD spectra, whereas binaphthalene conformational changes are mostly neglected both by theory and by experiment. In CD simulation by TD-DFT, CAM-B3LYP outperforms B3LYP and M06 by means of similarity analysis, whereas the last mentioned functional also delivers satisfactory performance qualitatively. The inclusion of dispersion corrections during geometry optimization was crucial to retain consistency with the measured spectra. By carefully considering all relevant conformations of this 20-membered macrocycle, reasonable agreement with the experiment is reached not only for the CD simulation of the individual conformers but also of the photoisomerization process of their admixture