A transition from a fluid to a constrained phase, in dilute solutions of a rodlike molecule, poly(2,5-dinonylparaphenylene ethynylene)s (PPE) in toluene has been studied, exploring the dynamics and the structure of the PPE molecules and the solvent in both phases. The transition is characterized by visual changes in the viscosity of the system and in its color, where a transparent liquid transforms into a yellow glassy phase. Nuclear magnetic resonance relaxation measurements indicated that significant restriction of motion of the solvent and of the polymeric molecule take place as the gel-like phase is formed. Small angle neutron scattering studies have shown that in the liquid phase, PPE forms molecular solutions where the molecules are fully extended. Upon transition into the constrained phase, aggregation of PPE molecules into large flat clusters occurs. When the aggregates are too large to freely move in the solution, a transition into a constrained phase takes place. The interaction between the highly conjugated PPE molecules and the solvent results in constraint of the motion of the solvent as well.