Phase Acrobatics: The Influence of Excitonic Resonance and Gold Nonresonant Background on Heterodyne-Detected Vibrational Sum Frequency Generation Emission

Christopher C. Rich, Kathryn A. Lindberg, Amber T. Krummel

Research output: Contribution to journalArticlepeer-review

6 Scopus citations

Abstract

We show how heterodyne-detected vibrational sum frequency generation (HD-VSFG) spectroscopy can discriminate between the excitonic and monomeric properties of a helical, nanotube molecular aggregate by monitoring the phase of the VSFG emission associated with different polarization configurations. By keeping track of the "phase acrobatics" associated with the added phase of the nonresonant SFG emission of gold as well as that of the double-resonance conditions achieved when the SF frequency is resonant with an electronic exciton transition, we discover that for aggregates of tetra(sulfonatophenyl)porphyrin (TSPP) the PPP-polarized spectra exhibit double-resonance conditions while SSP-polarized spectra exhibit resonance only with the ground-state vibration. Along with observed shifts in the vibrational frequency, intensity differences, and sign flips in the imaginary second-order susceptibility, χs,Im(2), we conclude that PPP-polarized HD-VSFG spectra reflect the delocalized, excitonic nature of the molecular aggregate, while the SSP-polarized HD-VSFG spectra measure the localized, monomeric nature of the molecular subunits. It is implied from this study that HD-VSFG spectroscopy can be uniquely utilized to measure the excitonic and monomeric properties associated with molecular assemblies for a single sample.

Original languageEnglish (US)
Pages (from-to)1331-1337
Number of pages7
JournalJournal of Physical Chemistry Letters
Volume8
Issue number7
DOIs
StatePublished - Apr 6 2017

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