Photoisomerization of N,N′-disubstituted indigos. A search for energy storage

Abstract

The photochemical behaviour of N,N1-disubstituted indigo dyes has been investigated. The trans to cis and cis to trans photoisomerization quantum yields are found to be of the order of 0.25 or less (down to 0.03). These dyes, which fluoresce only weakly in solution and at room temperature, show a drastic increase in their fluorescence when inserted into a polymer matrix or at 77 K in butyronitrile glass. This has been interpreted in terms of the inhibition of formation of a twisted excited intermediate as well as of the rotation of the substituent on the nitrogen atom. An important electron transfer occurs from the singlet excited state when the indigo dyes are placed in the presence of electron-donating molecules. When irradiating with visible light, the photostationary state is always in favour of the trans isomers. This, and kinetic as well as thermodynamic considerations, excludes these compounds as candidates for solar energy storage.JOSEPH POULIQUEN, VERONIQUE WINTGENS, VICENTE TOSCANO, BRAHIM BEN JAAFAR, SADHANA TRIPATHI, JEAN KOSSANYI et PIERRE VALAT. Can. J. Chem. 62, 2478 (1984.Le comportement des indigos substituks 1-4 a kt6 examink. On trouve que les rendements quantiques de photoisomerisation sont faibles (de l'ordre de, ou infkrieurs 9, 0,20). Ces composks qui fluorescent faiblement en solution et B 20°C, prksentent une augmentation considkrable de leur fluorescence quand ils sont inclus dans un polymkre ou bien lorsque la tempkrature est abaisske B 77 K dans le butyronitrile. Ceci a kt6 interpret6 comme un empschement a la rotation autour de la double liaison centrale, et comme une gene i la rotation du substituant sur l'azote ainsi que de l'inversion de cet atome. L'irradiation en lumi2re blanche est toujours en faveur des isomkres trans. Ceci, ainsi que des considkrations cinktiques et thermodynamiques excluent ces composks pour le stockage de l'tnergie solaire. IntroductionIn the search for new sources of energy, photochemical transformations have been examined as a potential means of obtaining energy-rich stable products. Criteria for efficient photochemical conversion of solar energy are: absorption in the visible or near-ultraviolet region, high quantum efficiencies, large positive ground state enthalpies, and stable photoproducts. In addition, the reactant must be inexpensive and not dangerous.The importance of dyes has been widely recognized in different converting systems related to photobiology (1,2), photoelectrochemistry (3, 4), and photochemistry (5).Photochemical systems mostly involve (Fig. 1) absorption of visible light by a reagent R to produce a high energy content product P which can later release the stored energy while reverting to the starting material. Among the systems reported thus far, one finds intramolecular cycloadditions (the best system investigated seems to be the norbornadiene-quadricyclane one (6) which can store about 26 kcal/mol(7)) and valence isomerization (such as the photochemical transformation of 1-methyl 5-phenyl A-2 pyrazoline into 2-phenylcyclopropylazo...

Trans to cis photoisomerization of N,N′-disubstituted indigo dyes via excited singlet states; a laser flash photolysis and steady state irradiation study

“…Data reported in the previous work (13) already indicate that the singlet lifetime 7, of the flexible trans molecules increases to a smaller extent than the corresponding fluorescence quantum yields when going from 25 to -196OC. To verify this important observation TS was now determined in the same solvent at these temperatures.…”

“…Singlet lifetimes were measured by excitation at 354 nm with an Applied Photophysics SP-1 single-photon counting fluorimeter, which was connected to an Ortec multichannel analyzer and a VAX 11/780 by first-The tram isomers were prepared according to the procedure of Ross and Blanc (3b) for 1 and by Posner's method for 2-4 (17); the cis order kinetics with a rate constant kobs = T-' < 2 X 10' S-I. isomers of 1-3 were the same as described previously (13). The rigid absorption spectra and lifetimes in the ks range were molecule 5 was prepared using a procedure adapted from the one recorded for the transient in dichloromethane solution and in a described by Engi (18).…”

“…5). Measurements at higher temperatures were unsuccessful because of the occurrence of thermal cis + trans isomerization (13,21).…”

Covalent functionalization of graphene by azobenzene with molecular hydrogen bonds for long-term solar thermal storage

“…Many photo-responsive molecules capable of undergoing photoisomerization are designed and prepared 5 6 , but none achieves long-term and high-density storage. Azobenzene derivatives (AZO) show the great potential for solar thermal storage due to good absorption at 350–450 nm, reversible isomerization and thermal reversion controlled by functional groups and steric structures.…”

Effects of Polar Substituents and Media on the Performance of N,N′‐Di‐tert‐Butoxycarbonyl‐Indigos as Photoswitches

“…Advancing the knowledge from previous similar studies, Huang et al . have recently published an extensive work on a large variety of N,N’‐di‐substituted indigos which revealed the influence of the electronics of the N ‐substituents on spectral and photophysical properties of the dyes including the rates of thermal cis → trans isomerization for which a strong dependence on substituent electronics was found.…”