Long-lived phosphorescence of arenes in complexes with cyclodextrins 2. Room-temperature phosphorescence of ternary complexes of naphthalene and phenanthrene with β-cyclodextrin and adamantane derivatives in the presence of oxygen

Abstract

Long lived room temperature phosphorescence (RTP) of arene-β cyclodextrin (β CD)-cage hydrocarbon complexes in the presence of oxygen was studied. Naphthalene d 8 , phenanthrene, and fluorene were used as arenes and adamantane, 1,3 dimethyladamantane, diamantane, and diadamantyl were used as the cage hydrocarbons (according to PM3 quantum chemical calculations, the use of these compounds might cause the appearance of long lived RTP). The RTP lifetime of the naphthalene d 8 -β CD-diadamantyl complex is 11.9 s at 20 °C.Studies of supramolecular systems are of considerable interest for basic research and practice because their components often possess new, unusual properties. For instance, in our previous study 1 we first showed that in a molecularly organized system based on aggre gated ternary complex naphthalene d 8 -β cyclodextrin (β CD)-adamantane (Ad) the probe molecule of naph thalene d 8 exhibits long lived room temperature phos phorescence (RTP) with a lifetime, τ, of 10.3 s in the presence of molecular oxygen (major quencher of phos phorescence under normal conditions). Removal of oxy gen from the sample results in an increase in τ to 15.5 s. This means that in the aggregates formed the naphtha lene d 8 molecule is reliably isolated from oxygen and in tra aggregate oxygen diffusion is essentially hindered. The results obtained suggested that other cage hydrocarbons used as the third components could also act as good/reli able "steric shields" and that in the complexes based on them the probe arene molecule will phosphoresce in the presence of oxygen.Room temperature phosphorescence of inclusion complexes of arenes with cyclodextrin in the presence of oxygen with RTP lifetimes of the order of a few millisec onds was reported in studies of complexes containing heavy atoms. 2-4 Under such conditions, the quenching action of oxygen is about three orders of magnitude weaker than in the samples characterized by the RTP lifetimes of the order of a few or tens of seconds. It is these complexes that were studied in this work. Naphthalene d 8 was mainly used as arene; the lifetime of phosphorescence of this compound in a frozen EtOH-isopentane-Et 2 O (2 : 5 : 5) solution is 18.3 s at 77 K. 5Taking into account the available conclusions and rec ommendations, 1 it was of interest to examine the possi bility of observing long lived RTP of β CD complexes with other arenes and cage hydrocarbons in the presence of oxygen. Essential conclusions drawn earlier are as fol lows. Long lived RTP appears only if poorly water soluble hydrocarbons are used as the third components of com plexes (this favors aggregation of the ternary complexes). The third component molecule must be sufficiently large to be strongly bound to the arene-β CD complex and to ensure efficient protection of naphthalene from collisions with oxygen molecules in the wide part of the β CD cav ity. These requirements are met by Ad and its derivatives. Therefore the set of the third components of the com * For Part 1, see Ref. 1.

Efficient metal-free organic room temperature phosphors

“…Alfimov and coworkers achieved long-lived RTP from arene-β-cyclodextrin (β-CD) cage–hydrocarbon complexes in the presence of oxygen. 94 Among the different combinations, the complex naphthalene-d 8 -β-CD cage ( Scheme 4 ) with various hydrocarbons showed variable RTP lifetime of 11.9 s for diadamantyl, 9.4 s for diamantine, and 10.3 s for adamantine in the presence of oxygen. However, the RTP lifetime of these complexes further increased in the absence of oxygen.…”