trans-cis Photoisomerization of a biomimetic cyclocurcumin analogue rationalized by molecular modelling

Cyclocurcumin is a natural compound extracted from turmeric and showing, in addition to antiinfective, antibacterial, and intinflammatory capabilities, solvent-dependent phtoswitching ability. The solvent-dependent photochemistry of cyclocurcumin has been rationalized on the basis of a competition between π-π* and n-π* states. Recently we have reported the synthesis of a biomimetic analogue showing enhanced photochemical properties and in particular presenting photoswitching capacity in various media. In the present contribution we rely on the use of molecular modeling and simulation, incuding density functional and wavefunction based methods to explore the excited states potential energy surface landscape. We see that the addition of a carbon-carbon double bond to the core of the natural compounds favors the population of the π-π* state, whatever the choice of the solvent, and hence leads to photoisomerisation, with fluorescence reduced to only a minor channel, rationalizing the experimental observations. In addition, the two photon absorption cross section is also strongly increased compared to the parent compound, paving the way to the use in biologically oriented applications.