Temperature-Dependent Photoisomerization Quantum Yields for Azobenzene-Modified DNA

We study the photoisomerization quantum yield of azobenzene-modified DNA as a function of temperature for various DNA sequences. We find that even though the photoisomerization quantum yield of free azobenzene is essentially temperature-independent, the trans -to- cis photoisomerization quantum yield depends strongly on temperature when the azobenzene is incorporated into DNA. We show that this temperature dependence is DNA-sequence-dependent and closely linked to the melting temperature of the host DNA. While the trans -to- cis isomerization quantum yield is sequence- and temperature-dependent, in contrast, the thermal cis -to- trans isomerization of azobenzene embedded in DNA is sequence-independent and exhibits Arrhenius-like behavior with an activation energy of 88.8 ± 0.693 kJ/mol and a smaller pre-exponential factor than free azobenzene, yielding first-order cis -to- trans kinetics with a rate constant of (2.08 ± 0.00952) × 10 –6 s –1 at 25 °C. These results provide an understanding of the azobenzene isomerization mechanisms in DNA sequences to enable more efficient design of optically reprogrammable nanomaterials and biosensors.