Room-Temperature Single-Molecule Infrared Imaging and Spectroscopy through Bond-Selective Fluorescence

Area of Science:

• Chemical Physics
• Spectroscopy
• Materials Science

Background:

• Infrared (IR) spectroscopy is vital for studying molecular vibrations and chemical properties.
• Analyzing single molecules offers unique insights but is challenging at room temperature.
• Developing methods for single-molecule IR analysis is crucial for understanding molecular properties.

Purpose of the Study:

• To develop and apply a high-throughput method for mid-IR structural probing of single molecules at room temperature.
• To investigate molecular properties like vibrational peaks, linewidths, and lifetimes at the single-molecule level.
• To explore the impact of dimerization on single-molecule IR spectra.

Main Methods:

• Utilized bond-selective fluorescence microscopy with narrowband picosecond mid-IR and near-IR double-resonance excitation.
• Captured and analyzed single-molecule images, polarization dependence, vibrational peaks, linewidths, and lifetimes.
• Performed quantum chemistry calculations to support observed spectral shifts.

Main Results:

• Observed consistent vibrational lifetimes from bulk to single molecules.
• Found twofold narrowing of linewidths and increased anisotropy at the single-molecule level.
• Detected unexpected peak shifts attributed to dimerization, confirmed by calculations.

Conclusions:

• Single-molecule IR spectroscopy provides crucial molecular information in ambient environments.
• The findings highlight the importance of analyzing individual molecules for functional imaging and fundamental property investigations.
• This technique advances the study of luminescent molecules and their properties.