Cycloreversion Dynamics of a Photochromic Molecular Switch via One-Photon and Sequential Two-Photon Excitation

Abstract

Ultrafast pump-probe (PP) and pump-repump-probe (PReP) measurements examine the ring-opening reaction of a photochromic molecular switch following excitation to the first and higher excited states. Sequential two-photon excitation is a sensitive probe of the excited-state dynamics, because the secondary excitation maps the progress along the S1 reaction coordinate onto the higher excited states of the molecule. In this contribution, secondary excitation at 800 nm accesses more reactive regions of the excited-state potential energy surfaces than are accessible with direct vertical excitation in the visible or UV. The quantum yield for cycloreversion increases by a factor of 3.5 ± 0.9 compared with one-photon excitation when the delay between the 500 nm pump and 800 nm repump laser pulses increases beyond ~100 fs, in contrast with a slower ~3 ps increase that was previously observed for one-color sequential excitation at 500 nm. The evolution of an excited-state absorption band reveals the dynamics of the higher-lying excited state for both one-photon excitation in the UV and sequential two-photon excitation. The spectroscopy and dynamics of the higher-lying excited state are similar for both excitation pathways, including a lifetime of ~100 fs. The complementary PP and PReP measurements provide a detailed picture of the ultrafast excited-state dynamics, including new insight on the role of excited states above S1 in controlling the photochemical cycloreversion reaction.

Two-photon absorption spectroscopy of stilbene and phenanthrene: Excited-state analysis and comparison with ethylene and toluene

“…The choice of stilbene is motivated by its interesting photochemistry, which includes cis/trans isomerization and electrocyclization pathways that represent the key reaction channels in many photochromic molecular switches. 13,[27][28][29][30][31][32][33][34] The 2PA spectroscopy of stilbene has been a subject of theoretical studies for several decades, 15,35,36 however, only a handful of studies have employed correlated many-body electronic structure methods. [37][38][39] To treat stilbene and larger conjugated systems, many studies employed semi-empirical approaches and timedependent density functional theory (TDDFT).…”

Development of High‐Performance Pyrimidine Nucleoside and Oligonucleotide Diarylethene Photoswitches

“…A remarkable feature of the nucleoside-based DAEs reported here is their exceptionally high cycloreversion quantum yield, which is of great interest, e.g., for applications as a short term information storage medium. [40,60,61] Based on our analysis of 26 nucleosidic DAEs, two dU switches (dU Ph t Bu , dU 2Py ) were identified as promising candidates for the incorporation into the T7 promoter to control the activity of its polymerase. The photochromism of the monomers was maintained in the environment of the oligonucleotide, and for dU Ph t Bu even in the duplex.…”

Development of High‐Performance Pyrimidine Nucleoside and Oligonucleotide Diarylethene Photoswitches

“…Ar emarkable feature of the nucleoside-based DAEs reported here is their exceptionally high cycloreversion quantum yield, which is of great interest, e.g.,for applications as ashort term information storage medium. [40,60,61] Based on our analysis of 26 nucleosidic DAEs,t wo dU switches (dU Ph t Bu ,d U 2Py )w ere identified as promising candidates for the incorporation into the T7 promoter to control the activity of its polymerase.T he photochromism of the monomers was maintained in the environment of the oligonucleotide,and for dU Ph t Bu even in the duplex. Thet ranscription rate of the polymerase was modulated with an up to 2.4-fold turn on/offfactor with as ingle modification site.F uture work will focus on increasing the turn-off factor of the transcription rate by modifying the template strand that is directly recognized by the polymerase.T his system offers great potential for the reversible optochemical control over genes of interest.…”