Supporting Information

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1 Supporting Information Aggregated States of Chalcogenorhodamine Dyes on Nanocrystalline Titania Revealed by Doubly-Resonant Sum Frequency Spectroscopy Sanghamitra Sengupta, Leander Bromley III and Luis Velarde* Department of Chemistry, University at Buffalo, The State University of New York, Buffalo, New York USA. * lvelarde@buffalo.edu Supporting information provided: S1.Dye stability over prolonged laser beam exposure. S2. Response from bare nanocrystalline TiO 2 film. S3. Chiral-sensitive SFG experiments. S4. Selected normal mode vectors. S5. ATR-FTIR spectra. S1

2 S1. Dye stability over prolonged beam exposure: In order to verify the absence of photodegradation in the dye films over the course of the experiment, we had recorded two spectra on the same spot for a film of dye-3. We found that there were no significant changes at the laser intensities specified in the text (significant deleterious effects were observed at higher visible power). The two spectra below represent the SFG response under SSP polarization combination at 609 nm visible excitation. They were recorded one hour apart from each other at the same spot of the film with acquisition times of 10 minutes. Figure S1:SFG response (SSP polarization combination) for dye-3 at 609 nm visible excitation. The black spectrum represents the first response (i.e. acquisition) and red spectra represents the SFG response after 58 minutes of continuous excitation in the same spot. S2

3 S2. Response from bare nanocrystalline TiO 2 film: In order to confirm the vibrational features between ( ) cm -1 dyes are strictly originated from the adsorbed molecules on TiO 2, we have collected SFG response from bare TiO 2 film prepared following the procedure described in the text. The average power used for infrared and visible pulses were 3 mw and 3.5mW respectively. The spectra for ssp and ppp polarization combinations were recorded for 5 minutes, background subtracted and normalized to total exposure time and the non-resonance response from a bare Au film. The wavelength for the visible beam was set at 660 nm. As it can be seen in figure S1, we found entirely flat lines (for both polarization combinations) from bare TiO 2 in the C-C and C-H stretching regions. Figure S2: SFG response of bare TiO 2 at ssp polarization combination. Left is the C=C stretching region and right C-H region. S3

4 S3. Chiral-sensitive SFG experiment: Dye-1 films were used in order to perform the chiral-sensitive experiments. We had chosen the PSP (P polarized SFG, S polarized Visible and P polarized IR) polarization combination in order to test any traces of macromolecular chirality. We used 690 nm as the visible wavelength, keeping the infrared frequency centered at 1500 cm -1. The spectra was taken using ~3mW IR power and ~0.3 mw visible power and was recorded for 5 minutes (same conditions as the spectra reported in the text for ssp and ppp polarizations). The spectra was processed in the same way as it was mentioned above. We have also observed no response (complete flat line) which indicates that we are likely probing a monolayer and not the bulk response from aggregated chiral films. Figure S3: PSP polarization spectra of dye-1 on TiO 2 S4

5 S4. Selected normal mode vectors: Below are the normal mode vectors calculated at the B3LYP/Def2-TZVP level of theory for the five intense SFG modes described in the text. Figure S4: Normal modes (harmonic) and displacement vectors as calculated via DFT. A sodium atom (magenta) was placed near the carboxylate group for charge balance. The vibrational frequencies were corrected by a 0.98 scaling factor. The unscaled frequencies are shown in parenthesis. S5

6 S5. ATR-FTIR spectra The dye-1 and dye-2 loaded TiO 2 films were used to get ATR spectra as well. The ATR instrument (Bruker Vertex 70) is setup for a single bounce from a ZnSe crystal with the IR signal bouncing off the crystal at a 45 angle. We averaged 250 spectra together for each sample with 4 cm -1 resolution. We used a concave rubber band baseline correction with 10 iterations and 64 base points. We used a dry air background. The light source was a Globar and the detector a liquid nitrogen cooled mercury cadmium telluride (MCT) detector. The ATR spectra for the films of dye 1, dye 2 and dye 3 in titania used in the DR- SFG experiments are presented below. Figure S5: ATR spectra of Dye-1 (left) and Dye-2 (middle) and Dye-3 (right) on TiO 2 surface S6