Two‐Way Molecular Switches with Large Nonlinear Optical Contrast

Abstract

Molecular switches: Highly efficient acido- and photoswitchable frequency doublers (see scheme) based on the indolinooxazolidine core are studied by means of hyper-Rayleigh experiments and quantum-chemical calculations.To optimize the nonlinear optical (NLO) contrast, a series of indolinooxazolidine derivatives with electron-withdrawing substituents in the para position on the indolinic residue have been synthesized. Their linear and nonlinear optical properties have been characterized by UV-visible absorption and hyper-Rayleigh scattering measurements, as well as by ab initio calculations. The two-way photo- or pH-triggered switching mechanism has been demonstrated by comparing the absorption spectra of the zwitterionic and protonated open forms (POF). Hyper-Rayleigh measurements have revealed that the second-order NLO contrast between the closed indolinooxazolidine and the open pi-conjugated colored forms remain very large upon substitution. Theory and measurements show that for the POFs the amplitude of the first hyperpolarizability follows the Hammett parameters of the withdrawing groups. However, because the measurements are performed in resonance, to recover this behavior, elaborate procedures including homogeneous and inhomogeneous broadenings, as well as single-mode vibronic structures are necessary to extrapolate to the static limit.

Indolinooxazolidine: A Versatile Switchable Unit

“…31,45 The redox potential of various 5,5′-disubstituted bithiophenes was already reported close to 0.53 V vs Fc/Fc + when it is substituted by two thiomethyl groups. Because of the absence of electrochemical data reported on indolinooxazolidines, CV experiments were carried out on 1a and 1b (Figure 4).…”

Hydrochromic molecular switches for water-jet rewritable paper

“…1a). 1-10 were synthesized 19,32 with a modified four-step procedure by using phenylhydrazines as starting materials, as shown in Fig. 2.…”

“…Leuco dyes 12,13 and photochromic compounds 14,15 have attracted much attention as new rewritable imaging dyes for rewritable paper. In particular, spiropyrans and related molecular switches, which are well known to undergo light-stimulated reversible isomerizations [16][17][18][19] between ring-closed forms (CFs) and ringopen forms (OFs) accompanied by significant colour changes, might be suitable candidates for the development of rewritable paper 20,21 . However, the prevailing colour-switching stimuli for these molecules are mainly UV/Vis 22,23 and acid/base 24,25 , which lead to problems, such as molecular degradation, potential safety issues and environmental hazards.…”

Computational study of chiral molecules with high intrinsic hyperpolarizabilities

“…In addition, experimental phenomena and results can be explained and rationalized by means of ab initio calculations, including frequency dispersion and solvent effects [23][24][25][26][27]. Theoretical investigations can design nonlinear optical materials and may provide avenues of experimental study [28,29].…”