Effect of pressure on the luminescence of a series of methoxy phenylacetylene dendrimers neat and in dilute solution in solid poly(tert-butyl methacrylate)

The effect of pressure up to 60 kbar was measured on the luminescence peak location and efficiency for a series of methoxy phenylacetylene dendrimers (MeO). Dendrimers MeO-3, MeO-7, MeO-15, MeO-31, MeO-63, and MeO-127 were studied as neat polymers. MeO-3, MeO-15, MeO-63, and MeO-127 were also investigated in dilute solutions in poly(tert-butyl methacrylate). According to measurements of the dilute solutions, there is a charge-transfer (CT) state that, for the smaller dendrimers, lies well above the π* state; for the larger dendrimers, it is the emitting state at 1 atm. With increasing pressure, the intramolecular CT state is rapidly stabilized, so that at high pressure the emission is from this state for all dendrimers. For the neat polymers, there is an initial redshift that reverses direction at a pressure that is higher for smaller dendrimers. This reversal is attributed to intermolecular CT. There may be changes in the molecular geometry and/or relative orientation of adjacent dendrimers that tend to stabilize the intermolecular CT in the solid state.