Proton N.M.R. of trismethylenemethaneiron tricarbonyl in a nematic liquid crystal

Single crystals of the cycloadduct of 1-(9-anthryl)-3-(1-naphthyl)propane (CANP) have been prepared, enabling a photochemical and photophysical study to be made of the anthracene-naphthalene sandwich pair in this material. The low temperature fluorescence spectrum is broad, exciplex in nature, and has a decay time of about 80 ns. This emission is quenched as the temperature is raised by a process which involves photocyloaddition of the pair. Arrhenius plots give an activation energy of about 600 cm^-1 for the photochemical process. The analogous photophysical properties have also been studied in methylcyclohexane glasses at 77 K and 60 K. Formation of the sandwich pairs at 77 K gives rise to a ‘ partially relaxed ’ pair having some structure in its emission spectrum and a shorter lifetime. Possible reasons for the differences in properties of sandwich pairs in methylcyclohexane glasses and the parent cycloadduct crystals are discussed. Very weak emission from the naphthalene moiety of monomer ANP has been observed at 77 K.