Isolation and characterization of conformational isomers ofN,N′-bis(3,5-dichlorosalicylidene)-2,2′-ethylenedianiline: crystal structure, photoluminescence, and density functional theory calculation

Abstract

We have isolated two isomeric solids 1 and 2 of N,N′-bis(3,5-dichlorosalicylidene)-2,2′-ethylenedianiline and characterized by IR, UV/Vis, X-ray powder diffraction, thermogravimetric analysis/differential thermal analysis, and X-ray crystallography. Although the solids are same formulas, each shows different colors and crystal structures. Orange solid (1) shows endo conformation while yellow solid (2) exhibits exo form depending on packing modes. UV/Vis spectra of 1 and 2 appear very similar patterns in the solid state; however, the bands of 1 are slightly red-shifted compared with those of 2. 1 displays a strong fluorescent emission band at~582 nm while 2 shows an intense fluorescent signal at~563 nm. The charge density populations of 1 and 2 have been studied by computational simulations using density functional theory at pbe1pbe/6-311G** level. The calculated highest occupied molecular orbital and lowest unoccupied molecular orbital energies of 1 and 2 confirm that charge transfer occurs within the organic molecules. The energy difference of HOMO-LUMO in 1 is smaller slightly than that of 2 about 0.05 eV (~17 nm).

A Visible‐Light‐Triggered Conformational Diastereomer Photoswitch in a Bridged Azobenzene

“…[1] It is usually challenging to identify and isolate the rotational or conformational isomersb ecause of low energy barriers of rotation at ambient temperature, unless by increasing sterich indrances to freeze the rotation as in the case of atropisomers. [2] To date, only af ew conformational isomers have been separated or isolated, mainly based on cyclic amide/peptides, [3] calixarenes, [4] catenane, [5] triptycene, [6] ethynylpyrene-substituted diacetylene, [7] salen, [8] and fullerene [9] structures. Most of them are in equilibrium in solution andc onvert thermally.L ight-triggered reversible transformation between rotational isomersw ould be of particulari nterest becausel ight is (ideally) non-destructive, and allows ah igh spatiotemporal control.…”

“…In the dark at 25 8C, the samples relaxed with ah alf-life of 1t o4h( CH 3 CN). Surprisingly,t he final absorption spectrum after thermalb ack-isomerization did not match the absorption spectrum before irradiation (Figure 2f or compound 5;S upporting Information, Figure S2 for compounds [6][7][8]. To investigate this phenomenon, we focused our study on compound (Z 1 )-5.I somerization of (Z 1 )-5 was monitored by 1 HNMR spectroscopy, whichs hows the appearance of two new species( I and II)u pon irradiation at 406 nm.…”