From photoisomerization to logic operations: a theoretical study of pseudo-hemiindigo derivatives

Over the last decades the hemiindigo photoswitches, derived from indigo dye, have gained attention because they uniquely absorb visible light in both isomeric states, making them suitable when high-energy UV light is undesirable. Here, the photophysical properties of a series of pseudo-hemiindigo derivatives with anthracene, naphthalene, phenanthrene, pyrene, and pyrrole, i.e., 1-L, L = An, Na, Ph, Pn and Pl, are studied via Density Functional Theory (PBE0, B3LYP, M06-2X, ωB97XD and CAM-B3LYP) calculations. Their cis-cis, cis-trans, and trans-trans isomerization processes are investigated as well as their effect on the absorption and fluorescence spectra of the molecules. The isomerization process affects the absorption and fluorescence spectra, i.e., shifts of up to 30 nm and 70 nm are observed, respectively while the transition state is shifted up to about 150 nm. Irradiation with light of 580-620 nm can induce photoisomerization around double bonds converting between cis and trans configurations depending on the L group. It is found that all have the potential to be used as two-input molecular logic gates, where two subsequent irradiations are used as inputs. Emission outputs at about 420, 450, 480, 540, 560, 630, 780 nm can be utilized as output to build AND and Converse Nonimplication logic gates.