π-Extended push-pull azo-pyrrole photoswitches: synthesis, solvatochromism and optical band gaps

A new family of push-pull biphenyl-azopyrrole compounds 3b-g and 4b-d was efficiently obtained via a Suzuki cross-coupling reaction between 2-(4′-iodophenyl-azo)- N -methyl pyrrole ( 1a ) or 3-(4′-iodophenyl-azo)-1,2,5-trimethyl pyrrole ( 2a ) and 4′-substituted phenyl boronic acids in excellent yields. The influence of the π-biphenyl backbone and pyrrole pattern substitution was correlated with their optical properties. Solvatochromic studies via UV-visible spectrophotometry revealed that the inclusion of a 4′-nitro-biphenyl fragment favors a red-shift of the main absorption band in these azo compounds compared with their non-substituted analogues. Likewise, optical band-gaps were estimated by means of electronic absorption spectra and correlated with TD-DFT studies. The pyrrole pattern substitution and the π-conjugated backbone exhibit a clear influence on their thermal isomerization kinetics at room temperature. In all cases, biphenylazo-pyrrole compounds lead to the formation of J-type aggregates in binary MeOH : H 2 O solvents. Under these conditions, compounds 3b-c undergo a water-assisted cis -to- trans isomerization at room temperature. New push-pull biphenyl-azopyrrole photoswitches are efficiently obtained via a Suzuki cross-coupling reaction, give rise to J-type aggregates in binary MeOH : H 2 O solvents and undergo a water-assisted cis -to- trans isomerization at room temperature.