Light Induced Processes in the Condensed Phase

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9421043 Hochstrasser This research is focused on two main areas arising from recent technological advances in optical and infrared femtosecond pulse generation and near-field microscopy. Linear and nonlinear infrared properties of materials in the teraherz and the vibrational fundamental region are now accessible with time resolution in the 40-160 fs regime. These methods will be used to determine directly the nuclear responses, over a wide frequency range, to charge reorganization in conjugated polymers, charge transfer complexes and their crystals. Impulsive excitations of the nuclear motions leads to wavepackets whose motion in time can be used to characterize the potential surfaces involved. The vibrational energy dynamics also will be studied directly. A complete study of the higher exciton states of materials with confined excitations on linear chains of polysilanes will be conducted to understand the excited states of such chains in which the electron and hole are more separated. The second area of the proposed research is concerned with the dynamics and electronic properties of organic nanoscale systems using near-field methods. The materials to be characterized include: self assembled monolayers of proteins (on semiconductors) that can undergo energy and electron transfer with single protein spatial resolution; polysilane films and stretched films in which linear chain excitations can be separately examined; aggregates of cyanine dyes having coherence lengths larger than the tip size of the near-field microscope; and organic nanoparticles that can be separately examined and their confinement properties characterized. %%% The proposed research is in two main areas arising from our recent technological advances in optical and infrared femtosecond pulse generation and near-field microscopy. The first involves characterization of the femtosecond vibrational and electronic responses of materials in the infrared region of the spectrum from close to zero frequency to 8000 cm-1. The second is the determination of optical properties of nanoscopic and low dimensional organic, bio and polymeric materials by means of the newly developed near- field picosecond time resolved microscopy. This work is important because: 1) infrared properties of materials, particularly organic and biomaterial are not widely explored yet, and 2) it allows examining nanoenvironment in materials on the scale of single, isolated molecule.