Hyper Rayleigh scattering from DNA nucleotides in aqueous solution.

Area of Science:

• Nonlinear optics
• Molecular biophysics
• Quantum chemistry

Background:

• Nucleotides are fundamental building blocks of DNA, crucial for genetic information storage.
• Understanding their electronic and optical properties is essential for molecular electronics and biophysics.
• First hyperpolarizability (β) quantifies a molecule's response to an applied electric field, indicating nonlinear optical behavior.

Purpose of the Study:

• To experimentally determine the first hyperpolarizability (β) of four DNA nucleotides: adenine, thymine, cytosine, and guanine.
• To investigate the symmetry of the first hyperpolarizability tensor through polarization-resolved measurements.
• To compare experimental results with theoretical calculations using Density Functional Theory (DFT).

Main Methods:

• Hyper Rayleigh scattering (HRS) technique was employed in aqueous solution at a non-resonant wavelength of 800 nm.
• Polarization-resolved HRS measurements were conducted to analyze the hyperpolarizability tensor.
• Density Functional Theory (DFT) calculations using the PCM-B3LYP/6-31G+(d) basis set were performed, including solvent effects.

Main Results:

• The first hyperpolarizability values ranged from 1.67 ± 0.15 × 10⁻³⁰ esu (thymidine-5'-monophosphate) to 1.76 ± 0.16 × 10⁻³⁰ esu (2'-guanosine-5'-monophosphate).
• Polarization studies provided insights into the symmetry and tensor elements of the first hyperpolarizability.
• Experimental values showed good agreement with DFT theoretical predictions.

Conclusions:

• The study successfully quantified the first hyperpolarizability of DNA nucleotides, revealing differences in their nonlinear optical responses.
• Experimental and theoretical methods provide complementary information on molecular hyperpolarizability.
• These findings contribute to the understanding of nucleotide photophysics and potential applications in molecular materials.