Non-linear surface spectroscopy of photoswitches annd photovoltaics

This thesis contains three different projects of surface specific non-linear spectroscopies. The work shown here both explores the limit of these methods and use them to under- stand molecular surfaces. The first part, is an implementation of the cross- correlated frequency-resolved optical grating (XFROG) algorithm. This method was developed to deconvolute the explicit time dependent field of an IR laser pulse from a time delayed SFG mapping. Unlike traditional XFROG algorithms, our approach relies on a non-iterative deconstruction procedure. We present a proof of concept set of experiments that confirm the validity of both the theory and the implemented XFROG algorithm. ❧ The second part of this thesis is an SFG study of the isomerization of azobenzene terminated SAMs. A novel synthesis for an azobenzene terminated alkane thiol is presented as well as chemical characterization of the product. A number of binary SAM devices were built of different dilutions of the azobenzene thiol mixed with an alkane thiol to examine at the role packing and intermolecular sterics have on the isomerization. VSFG was used to quantitatively study the vibrational modes, surface concentration of molecules, and molecular orientation in these samples. In situ SFG measurements were taken during isomerization of these films. It was observed that isomerization proceeded only for dilute films implying a steric inhibition of isomerization in neat films. Modeling was performed on the change of SFG signal observable upon isomerization, which implied that for the dilute SAMs there was a strong conformational bias in isomerization away from the surface. ❧ The last part of this thesis describes the construction of a new picosec- ond scanning SHG spectroscopy setup and it's application of this setup to study the electronic excitations at the buried lamellar donor/acceptor interface in solar cells. A new experimental setup was devised using a computer-controlled tuned of optical para- metric amplifier to allow for automated, rapidly scanning SHG spectra to be recorded. This apparatus was used to look at the differences between the P3HT/air and P3HT/C60 interfaces. Thickness dependent modeling was used to extrapolate the surface specific signal from the data taken as there is a bulk SHG contribution along with the surface specific signal. This technique was also used to look at some new red absorbing polymers, P3HTT-10%DPP and P3HTT-10%TPD.