Designing molecules with particular photochemical properties could be possible, say scientists in Germany. 

Pi-conjugated compounds have alternating single and multiple bonds in their structure. Their electrons are delocalised over the system and the optical and electronic properties of the materials are influenced by the strength of this conjugation. They can be used as materials for applications including organic light emitting diodes and molecular switches that are activated photochemically. 

Gernot Frenking and Israel Fernández at the Philipps University of Marburg found that the strength of pi-conjugation can be estimated using computational chemistry. 

Using a method known as energy decomposition analysis (EDA) they studied a group of pi-conjugated compounds called cyanoethynylethenes. They calculated the energy associated with the stabilisation of the molecules by the conjugation. There was a strong correlation between these energies and ¹³C NMR signals from the compounds which indicate the strength of conjugation. 

EDA could be used to quantitatively analyse conjugation. 'It would then be possible to make predictions about the strength of pi-conjugation. Considering the enormously important field of pi-conjugating molecules, this would make a large impact on the progress of the field,' said Frenking. 

Frenking also outlined the team's future plans: 'we are now investigating pi-conjugation and aromaticity in metallacyclic compounds including metallabenzenes. This is a big challenge because it involves the transition metal d(pi) orbitals.' 

Rachel Warfield