Design, Synthesis and Characterization of a Visible-Light-Sensitive Molecular Switch and Its PEGylation Towards a Self-Assembling Molecule

Abstract

HBDI-like chromophores represent a novel set of biomimetic switches mimicking the fluorophore of the green fluorescent protein that are currently studied with the hope to expand the molecular switch/motor toolbox. However, until now members capable of absorbing visible light in their neutral (i. e. non-anionic) form have not been reported. In this contribution we report the preparation of an HBDI-like chromophore based on a 3-phenylbenzofulvene scaffold capable of absorbing blue light and photoisomerizing on the picosecond timescale. More specifically, we show that double-bond photoisomerization occurs in both the E-to-Z and Z-to-E directions and that these can be controlled by irradiating with blue and UV light, respectively. Finally, as a preliminary applicative result, we report the incorporation of the chromophore in an amphiphilic molecule and demonstrate the formation of a visible-light-sensitive nanoaggregated state in water.

Keywords: HBDI-like chromophores; light-driven molecular switches; light-sensitive molecules; nanoaggregates; photoswitches; self-assembling molecules.

Figure 1

Design of the new LDMS 1 from GFP fluorophore through HBDI‐like photoswitch and its rational conversion in the functionalizable LDMS 2 and pegylated water‐soluble self‐assembling LDMS 3.

Figure 2

Left panel: Structure of the major isomer of compound 1 obtained by crystallographic studies. Ellipsoids enclose 50 % probability. Right panel: H‐bond interaction involving the pyrrolidinone moiety and short contacts in the crystal of model compound 1.

Figure 3

Comparison of the UV‐vis spectra of E‐1 (blue lines) and Z‐1 (red lines) registered at 0.02 mM in methanol.

Figure 4

Comparison of the ¹H NMR spectra (400 MHz, CDCl₃) of prototype molecular photoswitch E‐1 (A) with the mixture of the E and Z isomers at the PSSs reached after irradiation at 320 nm (B), 380 nm (C), and 440 nm (D).

Figure 5

Transient absorption data (ΔA, coded in flase‐color scale) as a function pump‐probe delay (ps) and probing wavelength (nm), recorded on a dichloromethane solution of E‐1 upon excitation at (A) λ_pu=290 nm and (B) λ_pu=450 nm, and the corresponding decay associated spectra (DAS) resulting from their global analysis (C) and (D), respectively.

Figure 6

Selection of kinetic traces recorded for a dichloromethane solution of E‐1 upon excitation at λ_pu=290 nm (solid lines) and their global fit (in green), for a selection of probing wavelengths. In panels B to D, the kinetic traces recorded at the same probing wavelengths for λ_pu=450 nm (grey stars) are overlapped (after normalization), showing that the only differences are (i) in the 5 to 10 ps range where the decay appears slightly slower when λ_pu=450 nm, and (ii) in panel C, where the overshoot around time zero for λ_pu=290 nm is the very short‐lived signature of the S_X ESA observed before internal conversion to S₁.

Figure 7

Comparison of the UV‐vis absorption spectra of the compound E‐ 3 in methanol (A), and water (B) at concentrations ranging from 0.1 to 0.01 mM. The methanolic solution of compound E‐3 follows the Lambert‐Beer law, however the spectra at different concentrations in this solvent are shown for a direct comparison with those recorded in water.

Figure 8

Comparison of ¹H NMR spectrum (400 MHz) of E‐3 in deuterated water (top trace), CD₃OD (bottom trace).

Figure 9

A) I₃₇₃/I₃₈₄ intensity ratio obtained from pyrene emission spectra in the presence of pure E‐3 as a function of the logarithm of its concentration in water. B) DLS size distribution histograms (by intensity and volume) of E‐3 dispersions in bidistilled water at concentration values of 0.1 mg/mL.

Figure 10

CryoTEM image (up panels) and TEM image (bottom panels) obtained with a water solution of 3 at a concentration of 10 mg/mL, i. e. well above its CAC.

Figure 11

Isomerization of compound E‐3 in deuterated water at ambient conditions. Comparison of ¹H NMR spectrum (400 MHz) of E‐3 in deuterated water (bottom trace) with that of the same solution obtained after four months storage at ambient conditions (middle trace). The top trace represents the spectrum obtained by addition of methanol to the water solution in order to break the aggregates; methanol was added immediately before of recording the spectrum.