Low energy excited state vibrations revealed in conjugated copolymer PCDTBT.

摘要: Low energy vibrations in the excited state have been hypothesized to play an important role quickly and efficiently generating free charges bulk heterojunctions of some conjugated polymer systems. While time-resolved vibrational spectroscopies seemingly are well poised address relationship between kinetics motions after initial photoexcitation, uncertainty measurement arises due overlapping signals difficulties assigning observed oscillatory molecular response. Here, we demonstrate a high sensitivity strategy distinguish signal oscillations originating from lab noise those origin order isolate low excited-state model copolymer PCDTBT. Furthermore, modes that may be implicated different kinetic pathways, coherent extracted 2-dimensional electronic spectroscopy (2DES) compared for two solvents with polarities resulting kinetics. We observe change solvent affects dynamics on >2 ps scale but not time required charge generation (∼200 fs scale). By same token, appear disappear based polarity also associated slower process. The observation coupled manifold persists through thus can fast process supports hypothesis direct polaron formation, rather than exciton formation diffusion followed by interfacial separation, is more likely route toward organic heterostructures.