Polysubstituted 5-Phenylazopyrimidines: Extremely Fast Non-ionic Photochromic Oscillators

Area of Science:

• Materials Science
• Organic Chemistry
• Physical Chemistry

Background:

• Photochromic systems are vital for developing advanced optical devices like photochromic oscillators.
• Achieving ultrahigh rates of thermal relaxation in photochromic materials is a key challenge.

Purpose of the Study:

• To design and investigate novel 5-phenylazopyrimidine derivatives with tunable thermal relaxation properties.
• To explore the potential of these molecules for efficient photochromic oscillator applications.

Main Methods:

• Density Functional Theory (DFT) calculations for in silico design and energy barrier analysis.
• Nuclear Magnetic Resonance (NMR) spectroscopy for structural confirmation of isomers.
• Transient absorption techniques to measure photoswitching parameters and thermal back-isomerization lifetimes.

Main Results:

• Designed 5-phenylazopyrimidines with strong push-pull characteristics and low energy barriers for (Z)-to-(E) isomerization.
• Confirmed the structure of the (Z)-isomer using low-temperature NMR with in situ irradiation.
• Demonstrated tunability of thermal back-isomerization lifetimes over 8 orders of magnitude (nanoseconds to microseconds) via substituent modification.
• Proposed a dominant rotation mechanism for (Z)-to-(E) thermal fading based on DFT calculations.

Conclusions:

• The designed 5-phenylazopyrimidines offer a promising platform for photochromic oscillators due to their tunable, ultrahigh thermal relaxation rates.
• Substituent engineering provides precise control over the lifetime of thermal back-isomerization.
• The findings contribute to the understanding of photochromic mechanisms and the development of advanced photoresponsive materials.