Stark profiles of singlet excitons in conjugated polymers Original Research Article

Electroabsorption (EA) spectra associated with overlapping vibronics of even- and odd-parity excitons are related in the Condon approximation to the linear absorption of discrete localized states. The EA intensity and profile depend strongly on the linewidth, Λ, with Λ−2 scaling of features due to Stark shifts and Λ−1 scaling of induced absorption and bleaching. Static disorder in polymer films broadens the linear absorption and reduces EA intensity compared to polydiacetylene (PDA) crystals, whose resolved spectra indicate overlapping vibrational sidebands. Similar excitations and transition moments in films conspicuously alter EA profiles and allow estimates of symmetry-breaking perturbations. EA spectra of PDA crystals and films are consistent with Pariser-Parr-Pople theory of linear and nonlinear optical spectra. The high sensitivity of EA also provides direct tests of excited-state displacements at induced transitions of even-parity excitons.