Photoisomerization of cis,cis-1,4-Diphenyl-1,3-butadiene in the Solid State:  The Bicycle-Pedal Mechanism

Abstract

The cis-trans photoisomerization of crystalline or powdered cis,cis-1,4-diphenyl-1,3-butadiene (cc-DPB) was studied at room temperature. The progress of the reaction was monitored by fluorescence spectroscopy, powder X-ray diffraction, 1H NMR and HPLC. High conversions (up to 90%) to the trans,trans isomer were observed in a crystal to crystal reaction. Formation of the cis,trans isomer, the sole product obtained in solution and in very viscous glassy media at 77 K is entirely suppressed in the solid state. The observed two-bond photoisomerization is explained by Warshel's bicycle-pedal photoisomerization mechanism (BP). The results are consistent with X-ray diffraction measurements, which have revealed that cc-DPB molecules exist in crystals in edge to face alternating arrays of two conformer structures whose phenyl rings deviate significantly from the plane of the central diene moiety ( approximately 40 degrees ). One of the conformers has the two phenyls in parallel planes and the other in roughly perpendicular planes. Least motion considerations suggest that the former should undergo the two-bond photoisomerization more easily, in agreement with observations that indicate that the reaction proceeds in discrete stages. Recently reported cis,cis- to trans,trans-muconate photoisomerizations in the solid state are proposed to also proceed via the BP mechanism. The reactions are consistent with the X-ray crystal structures of the cis,cis-muconate isomers.

Highly Emissive Nanostructured Thin Films of Organic Host–Guests for Energy Conversion

“…Figure 4 shows spectra typical of the trans conformer. A photoisomerization process is observed for the DPB molecules in DCA similar to that observed for DPB crystals by Saltiel et al, [21] even though we found that its evolution is much slower than that observed for the DPB molecules cast from solution (see the Supporting Information). Moreover, while in DPB films a decrease of the overall PL intensity is detected after photoisomerization, in DCA ICs the emission intensity is stable after prolonged lightexposure times.…”

“…The different absorption and PL properties of DPB s-trans and s-cis conformers have been used to study their equilibrium in solution [20] and photoisomerization processes in the solid state. [21] According to the preparation conditions of DPB and DPB-DCA, PL spectra of different mixtures of the two conformers are obtained (see the Supporting Information). Figure 4 shows spectra typical of the trans conformer.…”

Insights into the Origin of Solid‐State Photochromism and Thermochromism of N‐Salicylideneanils: The Intriguing Case of Aminopyridines

“…[1] This appealing switching phenomenon can be associated with a reversible modification of the geometrical structure, redox potential, dielectric constant, magnetic susceptibility and refractive index. [2] Photoinduced processes can involve interesting phenomena such as redox reaction, [3] electronhole pair generation, [4] spin crossover, [5] coordination change, [6] photocyclisation, [2] photoisomerisation, [7] tautomerisation [8] and bond cleavage. [8] Solid-state photochromism, which is rarely encountered, enables prospective potential applications in information storage, [9,10] molecular machines, [11] optical switches, displays, sensors [12] and in nonlinear optics.…”

Engineering Solid‐State Molecular Switches: N‐Salicylidene N‐Heterocycle Derivatives

“…[42] N-Salicylidene aniline derivatives are not the only possible candidates for light-induced information storage applications. Many others photochromic molecules have been described by using a large range of chemical reaction such as redox reactions, [43] electron-hole pair generation, [44] spin crossover, [45] coordination change, [46] photocyclization, [43] photoisomerization, [47] bond cleavage [48] and so on. Nevertheless, solid-state photochromism appears to be rare and only a few systems fulfill criteria for data storage applications.…”