Fluorescence emission and image patterning from selective photocyclic aromatization of cis–cisoid helical poly(phenylacetylene)s in situ in a film via top-down photodegradation

Selective photocyclic aromatization (SCAT) of cis–cisoid helical poly(phenylacetylene) derivatives was investigated during the in situ photodegradation in a film. An infrared absorption peak appeared at ∼1700 cm⁻¹ owing to the overtone vibration of the 1,3,5-trisubstituted benzene and the peak at 1060 cm⁻¹ due to the cis C=C bending of the main chain decreased, indicating occurrence of SCAT. Simultaneously, the polymer film became emissive in visible region during SCAT. The fluorescence (FL) quantum efficiency was approximately 0.92% in the film and not so much high relative to usual fluorophores. The FL emission disappeared in an instant when the decomposition product dissolved in a solvent. The FL lifetime of the polymer film increased with photodegradation. These all indicated the occurrence of excimer emission. A finely resolved FL image pattern was readily obtained using a photomask.