Ultrafast Z → E photoisomerisation of structurally modified furylfulgides

Abstract

Femtosecond broadband transient absorption spectroscopy has been used in a comparative study of the ultrafast photo-induced Z → E isomerisation reactions of four photochromic furylfulgides with selected structural motifs in n-hexane as solvent. The results show that all studied Z-fulgides exhibit fast and direct processes along barrierless excited-state pathways involving a conical intersection (CI) between the S1 and S0 electronic states. The excited-state lifetimes range from τ1 = 0.18 ps for the methyl derivative to τ1 = 0.32 ps for the benzofurylfulgide. The impulsive rise of the absorption by vibrationally hot Z- and E-isomers back in the electronic ground state following electronic deactivation and isomerisation indicates that the initially prepared wave packet persists even after passage of the CI. Furthermore, the results provide qualitative evidence for a quickly dephasing vibrational coherence in the electronic ground state. In contrast to the significant changes observed for the corresponding E- and C-isomers [Renth et al., Int. Rev. Phys. Chem., 2013, 32, 1-38], the excited-state dynamics of the Z-isomers is not affected by varied sterical hindrance from methyl and isopropyl substituents at the central hexatriene unit, or by intramolecular bridging, and remains unaltered upon extension of the π-electron system in a benzannulated furyl fulgide.

The ultrafast reactions in the photochromic cycle of water-soluble fulgimide photoswitches

“…6 The Z-and the E-forms have similar optical properties and can be interconverted using near UV light. 19 However, the photochromic reaction of interest with the strongest change of optical properties involves the electrocyclic ring-closing of the cyclizable open form to the thermally stable C-form ( Fig. 1).…”

Azobenzene C‐Nucleosides for Photocontrolled Hybridization of DNA at Room Temperature

“…The other approach uses reversible photoswitches that can exist in two stable states. Azobenzenes,21–23 spiropyrans,24–28 diarylethenes,29–33 fulgide,34–36 fulgimide,37, 38 hemithioindigos,39–41 and overcrowded alkenes42, 43 are prominent switches, and most of these switches have already been applied to the regulation of nucleic acids. For the light control of nucleic acids, the photoswitch itself and the linker that connects the photoswitch to the oligonucleotide are very important for an effective regulation event.…”

“…[9][10][11] Light control of nucleic acids can be divided in two major approaches:O ne method uses irreversibly removable photolabile protecting groups (cages), which can be applied,f or example, for the photoregulation of transcription [12][13][14][15] or antisense or micro RNA (miRNA) activity. [16][17][18][19][20] The other approachu ses reversible photoswitches that can exist in two stables tates.Azobenzenes, [21][22][23] spiropyrans, [24][25][26][27][28] diarylethenes, [29][30][31][32][33] fulgide, [34][35][36] fulgimide, [37,38] hemithioindigos, [39][40][41] and overcrowded alkenes [42,43] are prominent switches, and most of these switches have already been applied to the regulation of nucleic acids. For the light controlo fn ucleic acids, the photoswitch itself and the linkert hat connects the photoswitcht ot he oligonucleotide are very importantf or an effective regulation event.…”

Synthesis and photochromism of naphtho[2,1-b]furyl fulgides

“…Compound 14 absorbs in a somewhat shorter-wave region of the spectrum. Table 1 Irradiation of toluene solutions of fulgides 5E, 11E and 13E with light of 365 nm leads to the spectral changes characteristic of E/Z-isomerization processes 18,19 not followed by the formation of the ring-closed forms C, known to absorb in the visible region 20 (Scheme 3, Fig. 1).…”