Thermal-Induced Twisting and Photoinduced Planarization of Salicylideneaniline in Alcohols

Abstract

Thermofluorochromism and photochromism of salicylideneaniline (SA) in alcohol were investigated using steady-state and time-resolved fluorescence and absorption spectroscopy. The planar trans-enol form of SA in alcohols is converted into the twisted trans-enol form on heating. This conversion results change in the emission maximum from the 530 to the 440 nm region with an increase in fluorescence intensity, which confirms the absence of intramolecular hydrogen bonding between imine nitrogen and phenolic hydrogen in the twisted trans-enol form. The activation barrier for thermal-induced formation of the twisted trans-enol form in methanol was determined experimentally and was found to be 20.15 ± 2.22 kcal/mol. The rotation of the phenolic C 7 −C 8 and C 7 −N 1 bond followed by breaking of the intramolecular hydrogen bond and formation of an intermolecular hydrogen bond with alcohol solvent molecules results in the thermally stable twisted trans-enol form in alcohol solvents. The biexponential nature of the fluorescence decay of the twisted trans-enol form of SA confirms that the emission originates from multiple (π−π* and n−π*) excited states. On photolysis under UV light, the twisted trans-enol form is converted back into the planar trans-enol form. The time-resolved absorption and excitation-resolved fluorescence spectrum of SA in methanol confirm the existence of the twisted cis-keto form as a transient photochromic intermediate in the light-induced planarization of SA in alcohols. In alcohols, an interplay between the intra-and intermolecular hydrogen-bonding controls excited-state reaction dynamics and conformational relaxation of SA, which are responsible for the photochromism of salicylideneaniline.

Ultrafast Response Organic Photoswitch Materials and Their Application in Volumetric 3D Display

“…The negative absorption at 370 nm is related to the bleaching signal of the initial ground state . The maximum transient absorption at 460 nm is assigned to the unstable keto form formed by ESIPT, which is consistent with the results of the femtosecond transient absorption . With increasing delay time, the keto form of NS 1 spontaneously transforms to the initial enol form at 25 °C.…”

“…42 The maximum transient absorption at 460 nm is assigned to the unstable keto form formed by ESIPT, which is consistent with the results of the femtosecond transient absorption. 43 With increasing delay time, the keto form of NS 1 spontaneously transforms to the initial enol form at 25 °C. The decay curve of NS 1 at 460 nm follows first-order kinetics, and the half-life of the thermal recovery was 10.62 ms (Figure 3d).…”

Light-Driven Domain Switching on a Photochromic Ferroelectric

“…Under the ambient condition, t Bu-2-FSA possessed the enol form in the solid state, as depicted in Figure b. The plausible mechanism for photochromism is the proton transfer-induced structural transition, where proton transfer from the hydroxyl group (enol form) to the nitrogen and lead to the formation of ketone (trans–keto form). − We also checked the thermal transformation of t Bu-2-FSA from the trans–keto form to enol form by the color change (Figure S3). As shown in Figure c, in order to investigate the photochromic properties, UV–vis absorption measurements were conducted by various light irradiation treatments.…”

Pillar[5]arene-Based Co(III)-Loaded Covalent Organic Polymer for Efficient CO2 Cycloaddition under Mild Conditions

“…■ EXPERIMENTAL SECTION Chemicals and Materials. 3,3′-Bis-(((4-hydroxyphenyl)imino)methyl)-[1,1′-biphenyl]-4,4′-diol (BHPD−OH) 72 and per-(2-bromoethyl) pillar[5]arene (BrP5) 73 were synthesized according to reported methods. All epoxides were purchased from Energy Chemical Co. Ltd (Shanghai, China) in their purest forms.…”