Anthracene monolayers, photodimerization

The opposite behaviour, namely photodimerization, can take place when local concentrations of substrate are high, as for anthracene in Langmuir-Blodgett monolayers." In fact, this is a common reaction pathway for anthracene derivatives and occurs by both bimolecular and intramolecular routes. The efficiency of intramolecular photocyclization depends on the length and flexibility of the connecting chain. 

Monolayers of anthracene modified with an cv-mercaptoalkane chain undergo photodimerization upon irradiation at 350 nm (equation 10). This process is confirmed by fluorescence and FT-IR measurements. The reaction can be reversed by irradiation at 254 nm, similar to the same process in the bulk medium. In the reverse reaction photodecomposition results in a partial loss of anthracene341. 

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