This paper compares the inhibition effect of porphyrin aggregation in the presence of urea, guanidinium chloride (Gdn) and sorbitol by molecular dynamics simulation. It demonstrates that porphyrin aggregation increases in sorbitol, but decreases towards addition of urea and Gdn. It shows that urea, Gdn and sorbitol can have a large effect — positive or negative, depending on the concentration — on the aggregation of the porphyrin. The effect of urea, Gdn and sorbitol on porphyrin aggregation has been inferred from the effect of these solutes on the hydration layer of porphyrin. It appears that the Gdn is more suitable than urea for decreasing the hydration layer of porphyrin while several osmolites like sorbitol are known to increase hydration layer and thus might stabilize the porphyrin aggregation. Results of radial distribution function (RDF), distributed atoms or molecules around target species, indicated that the increase and exclusion of solvent around porphyrin by osmolytes and Gdn would affect significantly on porphyrin aggregation. There was a sizeable difference in potency between the Gdn and urea, with the urea being less potent to decrease hydration layer and porphyrin aggregation.

This work presents a combined experimental and theoretical study on a photochromic compound, 2-([1,1'-biphenyl]-4-yl)-2-methyl-6-(4-nitrophenyl)-4-phenyl-1,3 diazabicyclo [3.1.0]hex-3-ene, existing in closed form (‘A’) and open form (‘B’). The spectroscopic properties of the title compound have beeninvestigated by using IR, UV–Vis and ¹H NMR techniques. The molecular geometry and spectroscopic data of the title compound have been calculated by using the density functional method (B3LYP) invoking 6-311G(d,p) basis set. UV-Vis spectra of the two forms were recorded. The excitation energies, oscillator strength, etc., were calculated by time-dependent density functional theory (TD-DFT). Furthermore, molecular electrostatic potential map (MEP), frontier molecular orbital analysis (HOMO–LUMO), total density of state (TDOS) and reactivity descriptors were found and discussed. We applied a first-principles computational approach to study a light-sensitive molecular switch. We find that the conductance of the two isomers varies dramatically, which suggests that this system has potential use as a molecular switch.