[2 + 2] cycloaddition and its photomechanical effects on 1D coordination polymers with reversible amide bonds and coordination site regulation

Photo-responsive materials can convert light energy into mechanical energy, with great application potential in biomedicine, flexible electronic devices, and bionic systems. We combined reversible amide bonds, coordination site regulation, and coordination polymer (CP) self-assembly to synthesize two 1D photo-responsive CPs. Obvious photomechanical behavior was observed under UV irradiation. By combining the CPs with PVA, the mechanical stresses were amplified and macroscopic driving behavior was realized. In addition, two cyclobutane amide derivatives and a pair of cyclobutane carboxyl isomers were isolated through coordination bond destruction and amide bond hydrolysis. Therefore, photo-actuators and supramolecular synthesis in smart materials may serve as important clues.


Materials and methods
All reagents and solvents used in the experiments are commercially available and require no further purification.Elemental analysis (C, H, N) was performed using an Elemental Vario ELIII analyzer.The NMR spectroscopy was recorded on the Bruker ADVANCE III HD400 (400 MHz) spectrometer with TMS in DMSO-d 6 solution as the internal reference and chemical shifts reported in parts per million (ppm).The mass spectra were recorded on the Agilent LC-MSD TOF mass spectrometer.Infrared (IR) spectra were recorded using KBr particles (4000-400 cm -1 ) on Thermo Fisher Scientific FTIR-Nicolet iS10.All PXRD analyses were performed using the Rigaku TTRⅢ-18KW automatic diffractometer (Cu Kα, 1.5418 Å), scanning from 3° to 55° with a scanning step size of 0.01°.Thermal stability studies were carried out in a nitrogen atmosphere at a heating rate of 10 ℃ min -1 on a Mettler-Toledo synchronous thermal analyzer.The morphology and energy dispersion spectroscopy (EDS) data of the composite films were obtained by NovanoSEM 450 field emission scanning electron microscope (SEM) at 10 kV.Uv diffuse reflectance spectroscopy measurements were recorded by Hitachi U-4100 spectrograph, containing an integrating sphere, with BaSO 4 plate as standard (100% reflectivity).Fluorescence measurements were made with a cold light F98 fluorescence spectrophotometer.

Separation of cyclobutanyl carboxylic acid dimer L 4 .
A mixture of 2a (0.1 mmol, 78.46 mg) and HCl (36%, 25 mL) were added to a 50 mL beamer, stirred at room temperature for 30 minutes, and then pumped and filtered.The filtrate was condensed and returned at 110 ℃ for 1 day, washed by centrifugation and ultra-pure water, and dried in the oven.The black powder separated was cyclobutanyl carboxylic acid dimer L 2 .Yield: 22.9 mg (74.3%, based on 2a).Anal

X-ray crystallography
A selected single crystal of suitable size was mounted on a glass capillary tube for X-ray diffraction analysis.Crystallographic data were collected using graphite monochromatic Mo-Kα radiation (λ=0.71073Å) and the ω-scanning techniques on a Bruker Smart AXS CCD diffractometer 1 .The SADABS program was used to modify the experience absorption.In each case, the structure was solved using the SHELXL software package and the SHELX-2014 program was refined by the F 2 -based full matrix least square method 2,3 .All non-hydrogen atoms were located in a different Fourier synthesis and finally refined with anisotropic thermal parameters.Table S1 lists the crystallographic data and details of data collection and structure refinement for 1-2a.Tables S2   and S3 list the selected key lengths and angles for 1-2a, respectively.CCDC:

Simulation details
The data of powder x-ray diffraction were recorded on Bruker D8 advance diffractometer (40 kV, 40 mA) with step of 0.01 degree from 3° to 55° at room temperature, using graphite monochromator and Cu-Kα radiation (λ=1.5418Å).The positions of the peaks were picked up from the diffraction pattern excluding the weak peaks agreeing with the reactant, they were further applied to index and yield the unit cell parameters by TOPAS 4,5 program, subsequently an empty cell was constructed according to the enforced unit cell parameters, and the atoms were added to it and refined to find their ideal positions by TD-DFT method using GGA-PBE function.The final structure was checked through comparing the x-ray diffraction pattern between the experimental line and theoretical one (figure S3), their positons matched each other well and revealed the correction for the final structure.Mass spectra

Fig. S30 the
Fig. S30 the direct optical band gap.

Fig. S32
Fig. S32 SEM image and EDS mapping images of 2-PVA membrane.

Fig. S34
Fig. S34 Under UV light, the single crystal 2 becomes crystal 2a, and the cell volume shrinks twice.

Fig. S36
Fig. S36 Optical images of the composite membrane 1-PVA upon exposure to 365 nm light.

Fig. S37
Fig. S37 Optical images of the composite membrane 2-PVA upon exposure to 365 nm light.

Fig. S39
Fig. S39 AFM images and the corresponding height profiles of a section of a line in 1-PVA (a, b) and irradiated 1-PVA membrane (c, d).

Fig. S40
Fig. S40 AFM images and the corresponding height profiles of a section of a line in 2-PVA (a, b) and irradiated 2-PVA membrane (c, d).

Table S1
Crystallographic data and structure refinement summary for 1-2a.

Table S6
Single crystal data.