Resonance photoionization of a diarylethene derivative in the presence of cyclodextrins using multi-color multi-laser irradiation

Abstract

Abstract Photochromism is isomerization of a molecule induced by light, and is attractive for applications like actuators and optical memory. However, the photodynamics of photochromic materials under excitation by three lasers at three different wavelengths are poorly understood. In this article, we investigate the properties of the well-known photochromic material 2,3-bis(2,4,5-trimethyl-3-thienyl) maleic anhydride (1) upon excitation by one, two and three lasers. In these experiments, α-, β- and γ-cyclodextrin (CD) are added to 1 to form inclusion complexes to improve the solubility of 1 in water/acetonitrile. First, the formation of 1/CD inclusion complexes is evaluated by changes in the 1H NMR spectrum of 1 and calculations. We find that the area of each molecule of 1 in the 1/CD inclusion complexes exposed to the solvent depends on the cavity size of the CD, and that the CD also affects the ratio of the antiparallel and parallel conformations of the open form (OP) of 1. The transient absorption of hydrated electrons in the 1/CD systems is then observed at 720 nm by flash photolysis using one laser (266 nm), two lasers (266 and 532 nm) and three lasers (266, 532 and 355 nm). The ionization quantum yields of 1 depend on both the type of CD present, which is rationalized by the ability of 1 to isomerize in the different-sized cavities of α-, β- and γ-CD, and on the laser pulse configuration. The ionization efficiency obtained using the two-laser system is higher than that measured with the one-laser system. This confirms that two-photon ionization of 1 proceeds through two-step two-photon excitation with S0 → S1 and S1 → Sn singlet-state transitions. The photoionization efficiency of 1 in the presence of CDs determined using three laser pulses increases upon opening of the closed-ring isomer (CL) of 1 by 532 nm irradiation (the second laser pulse). This effect is particularly obvious in the presence of γ-CD. This investigation of the photodynamics of 1 in inclusion complexes using multiple lasers contributes to our understanding of how we can influence photochromism using host species and different laser wavelengths.