Dyes included in channels: effects of the confinement on the photoexcited triplets. A TR-EPR study

The photoexcited triplet states of different pi-conjugated organic dyes, included in segregating matrices of organic hosts with channel-like cavities, have been studied by time resolved-EPR. The dyes have been studied also in glassy phases and the triplet spectra in different matrices have been compared with each other to study the effects of the confinement on the guest molecules. We studied some nitro-substituted diphenyl polyenes and oligothiophenes as guests in self-assembling inclusion compounds with perhydrotriphenylene or tris-o-phenylenedioxicyclotriphosphazene. We observed three possible effects of the inclusion on the conformations of the guests: a reduced number of conformations due to the geometrical constraints; an increased number of conformations due to the stabilizing host-host interactions; peculiar conformations determined by head-to-tail interactions with the neighbours along the channel.