Abrupt exciton self-trapping in finite and disordered one-dimensional aggregates

We show that in finite, disordered one-dimensional aggregates the exciton self-trapping takes place at significantly weaker exciton-lattice coupling than it is known for the regular infinite lattices. A series of abrupt changes of self-trapped exciton energy and other parameters can take place at multiple critical couplings, depending on initial exciton amplitude distributions. These states vary by the wave function localization at different segments of the aggregate. The observed energy splitting suggests a coexistence of two or more types of self-trapped excitons with altered lattice reorganization energy. This provides a general explanation for several recent spectroscopic observations on photosynthetic antenna complexes.