Photochemical properties of multi-azobenzene compounds

Abstract

A systematic study is reported of the photochemical properties of the multi-azobenzene compounds bis[4-(phenylazo)phenyl]amine (BPAPA) and tris[4-(phenylazo)phenyl]amine (TPAPA) compared to the parent molecule 4-aminoazobenzene (AAB). The bis- and tris-azobenzenes were synthesised by a variant of the Ullmann reaction and exist in their stable all-E forms at room temperature. Striking changes in the spectral positions and intensities of their first ππ* absorption bands compared to AAB reveal strong electronic coupling between the AB units. The nature of the excited states was explored by quantum chemical calculations at the approximate coupled-cluster (CC2) level. Upon UV/VIS irradiation, the molecules isomerise to the Z-isomer (AAB), ZE- and ZZ-isomers (BPAPA), and ZEE-, ZZE- and ZZZ-isomers (TPAPA), respectively. The photoswitching behaviours were investigated by UV/VIS and NMR spectroscopies. All individual isomers were detected by one-dimensional (1D) (1)H NMR spectroscopy (BPAPA) and two-dimensional (2D) HSQC NMR spectroscopy (TPAPA). A kinetic analysis provided the isomer-specific thermal lifetimes. The variance of the thermal lifetimes demonstrates a dependence of the Z-E isomerisation on the chromophore size and number of AB units.

The Kinetics of the Cis-to-Trans Thermal Isomerization of 4-Anilino-4’- Nitroazobenzene are Highly Influenced by Solvent Polarity

“…This pronounced red-shift of ~60 nm can be rationalized by hydrogen bond formation between the solute and the solvent and a more stable zwitterionic form of the dye in the more polar solvents. Additionally, the polarity of the solvent may affect the N-N-C angle and the energy of electronic transitions of the N=N bond [16,17]. Figure 5 shows the typical absorbance change vs. time when a 4A4NAB dye solution is excited with a camera flash.…”

Vibronic and cation spectroscopy of selected rotamers of 4-chloro-3-fluorophenol

“…Investigations on the molecular structure can help us have insights into site specific intermolecular interactions in biological processes [1][2][3][4][5]. For this purpose, phenol and its halo-substituted species have been studied extensively by various spectroscopic methods [6][7][8][9][10][11][12][13][14].…”

Spectral and time-resolved properties of novel hetarylazo dyes containing hydrogenated quinolines and triazole moieties

“…The high potential of the use of aromatic azo dyes is based on the reversibility of the process, in which the molecular size, shape, and dipole moment dramatically change on going from the extended trans isomer to the more compact cis isomer [4,5]. Therefore, great attention is paid to the synthesis of new aryl and hetarylazo compounds with given prop erties [6][7][8][9]. The introduction of donor and acceptor groups in azobenzene, as well as the use of condensed aromatic and heterocyclic structures results in a bathochromic shift of the long wavelength absorption band and in an increase in the absorption coefficient of these compounds.…”