An ultrawide-range photochromic molecular fluorescence emitter

Photocontrollable luminescent molecular switches capable of changing emitting color have been regarded as the ideal integration between intelligent and luminescent materials. A remaining challenge is to combine good luminescence properties with wide range of wavelength transformation, especially when confined in a single molecular system that forms well-defined nanostructures. Here, we report a π-expanded photochromic molecular photoswitch, which allows for the comprehensive achievements including wide emission wavelength variation (240 nm wide, 400–640 nm), high photoisomerization extent (95%), and pure emission color (<100 nm of full width at half maximum). We take the advantageous mechanism of modulating self-assembly and intramolecular charge transfer in the synthesis and construction, and further realize the full color emission by simple photocontrol. Based on this, both photoactivated anti-counterfeiting function and self-erasing photowriting films are achieved of fluorescence. This work will provide insight into the design of intelligent optical materials.


A. Supplementary Methods
Materials: Chemical reagents are purchased from commercial resource and used without further purification.2,3,3-Trimethylindolenine is purchased from Aladdin Reagent (Shanghai) Co., Ltd.Propane sultone is purchased from Energy chemical Co., Ltd., 2-hydroxybenzaldehyde and 1-pyrenylboronic acid are purchased from Bidepharm.Pd(PPh3)4 is purchased from Leyan.Other solvents are purchased from Sinopharm Chemical Reagent Co., Ltd.
Then, the reaction solution was dropped into ethyl acetate at room temperature.The purple solid was collected by filtration, washed with ethyl acetate and n-hexane three times to obtain 15.2 g product (yield: 91.18%). 1  DFT calculations: All the DFT calculations were performed by the Gaussian 16 package 2 .The molecular orbital energies of PMC and PSP were performed with B3LYP functional with 6-31+G basis set. 3 For molecular dynamics, geometry optimization of all structures was performed using the M06-2X functional 4 , with the 6-31+G(d,p) basis set [5][6][7] .Frequency calculations were performed to obtain the Gibbs free energy correction at 298.15 K. Single point calculations were performed with the 6-311+G(d,p) basis set 8 .The SMD implicit solvation model 9 was used for all calculations with DMSO as the solvent.The molecular geometry and isosurface were plotted with CYLView 10 .
1 H-NMR test of PSP: PMC (10 mg) is dissolved in 500 ml CHCl3 and irradiation by the 500 nm light (~15 mW cm -2 ) about 1 hour (according to the UV-Vis spectra results).
Then the solution was concentrated quickly in room temperature (20-25 ºC).Obtained solid was dissolved in DMSO-d6 for 1 H-NMR test.The 1 H-NMR spectra of PSP are shown in Fig. 2b and Supplementary Fig. 30.

B. Supplementary Notes 1. Photophysical properties of PMC and PSP.
Supplementary Fig. 4. The investigation of the photoisomerization processes of PMC with varying light wavelengths.UV-Vis spectra and nonlinear fitted plot of photoisomerization processes of PMC state (red line) and obtained PSP state (black line) upon irradiation with different light wavelength at 420 nm (a, g), 475 nm (b, h), 500 nm (c, i), 550 nm (d, j), 600 nm (e, k) and 650 nm (f, l) in CHCl3. 1.The absorbance and concentration of photoswitch in chloroform before irradiation and after irradiation, absorbed photon flux, photoisomerization extent and quantum yield on photoisomerization processes with different light wavelength.Supplementary Fig. Supplementary Table 5.The parameters of first-order kinetic equation for photoisomerization processes based on time-dependent fluorescence intensities.Supplementary Fig. 16.The half-lives of five thermal relaxation processes with emissions at 640 nm and 400 nm.

Supplementary Table
of photoisomerization and thermal relaxation processes and fluorescence spectra for photoswitch in toluene.(g, h) The UV-Vis and fluorescence spectra of photoswitch in H2O.
Supplementary Table 6.Summary for maximum absorption and photoisomerization extent of the photoswitch in different solvents based on UV-Vis spectra.

7 .
The SEM-EDS analysis of PMC self-assemblies.(a) The dot scan of SEM-EDS of self-assemblies of PMC.The element analysis of dot 1(b) and dot 2 (c).
Photoisomerization extent of light irradiation (%) a

a, b
According to the experimental results, PSP shows negligible contribution to the certain absorbance.Therefore, we consider the absorbance decreasing efficiency as the photoisomerization extent.Supplementary Fig.19.UV-Vis spectra of photoswitch in DMSO/CHCl3 mixed solvents.The UV-Vis spectra of photoswitch in PMC state (a) and PSP state (b) in DMSO/CHCl3 mixed solvents with DMSO fraction from 0 to100%.

Table 2 .
The element content of scan dot from SEM-EDS in CHCl3.
11te: a, the Photon flux is measured by a quantum par meter (AZ Instrument crop., AZ8583) before and after putting the quartz cell with solution as soon as possible.b,thequantumyieldis calculated from initial rate divided by absorbed photon flux11, the light contact surface is 3 × 10 -4 m 2 and the volume of solution is 3 mL.C.Supplementary Notes 2. Investigation of ICT and self-assembly behavior of PMC.Supplementary