Molecular Engineering for Nonlinear Fluorescence: En Route to Three-Photon Absorption via Sequential One-Photon...

Area of Science:

• Chemical Physics
• Biophotonics
• Materials Science

Background:

• Multiphoton excitation (MPE) offers advantages like 3D confinement and reduced background in fluorescence imaging.
• MPE is limited by the requirement for high light intensities and long excitation wavelengths.

Purpose of the Study:

• To develop a molecular strategy that mimics MPE's nonlinear fluorescence response using sequential one-photon excitations (1PE).
• To overcome the technological limitations associated with conventional MPE.

Main Methods:

• Synthesized a dyad (2for1) comprising acedan and a spironaphthopyran photoswitch.
• Developed a triad (3for1) by incorporating a BODIPY photocage into the dyad.
• Investigated the fluorescence emission intensity's dependence on excitation intensity for both constructs.

Main Results:

• The dyad (2for1) demonstrated a quadratic dependence of emission intensity on excitation intensity, emulating two-photon absorption.
• The triad (3for1) exhibited an even stronger nonlinear fluorescence response.
• Sequential 1PE successfully reproduced multiphoton-like nonlinear optical phenomena.

Conclusions:

• Sequential 1PE provides a practical alternative to MPE for achieving nonlinear fluorescence.
• This strategy circumvents the high light intensity and wavelength limitations of MPE.
• The developed molecular constructs offer a pathway for advanced nonlinear optical imaging.