Optical Writing and Reading with a Photoactivatable Carbazole Electronic Supplementary Material (esi) for Physical Chemistry Chemical Physics

The fluorescence of a carbazole chromophore can be activated irreversibly under optical control with the photoinduced opening of an oxazine ring. In proximity to silver nanoparticles, the quantum efficiency of this photochemical transformation and that of the emissive process increase significantly. The plasmonic effects responsible for such enhancements, together with the photochemical and photophysical properties engineered into this particular photoactivatable fluorophore, permit the optical writing and reading of microscaled patterns at low illumination intensities.


Experimental Procedures
Synthesis.Chemicals were purchased from commercial sources and used as received with the exception of MeCN, which was distilled over CaH2.Compounds 3 and 4 were prepared according to literature procedures.S1,S2 ESIMS were recorded with a Bruker micrOTO-Q II spectrometer.NMR spectra were recorded with a Bruker Avance 400 spectrometer.

2.
A solution of 3 (1 g, 4.78 mmol), 5 (800 mg, 5.02 mmol) and TFA (20 µL, 0.26 mmol) in EtOH (20 mL) was heated under reflux for 18 hours.After cooling down to ambient temperature, the solvent was distilled off under reduced pressure.The residue was purified by column chromatography [SiO2: hexane:CH2Cl2 (7:3 v/v) → CH2Cl2/AcOEt (7:3 v/v)] and crystallized from hexane to give 2 (450 mg, 1.28 mmol, 27%) as a yellow solid.Absorption and Emission Spectroscopies.Absorption spectra were recorded with a Varian Cary 100 Bio spectrometer, using quartz cells with a path length of 1.0 cm.Emission spectra were recorded with a Varian Cary Eclipse spectrometer in aerated solutions.Fluorescence quantum yields were determined with a 9,10diphenylanthracene standard, following a literature protocol.S3 Samples were illuminated with a Luzchem Research LZC-4V photoreactor (350 nm, 4.88 mW cm −2 ) for the experiments in Figures 2 and 3. Fluorescence decays (Table S1 and Fig

S3
Square Wave Voltammetry.Voltammograms were recorded with a CH Instruments 610A electrochemical analyzer in MeCN under Ar, using a three-electrode cell.The reference was a Ag/Ag + electrode (1 mM AgNO3 in MeCN).The counter and working were a platinum wire and a glassy-carbon electrode respectively.The supporting electrolyte was Bu4NPF6 (50 mM).The scan rate was 50 mV s -1 .Silver Nanoparticles.Aqueous NaOH (1.2 M, 0.1 mL) was added to aqueous AgNO3 (0.22 g, 26 mL) under vigorous stirring.A dark-brown precipitate formed immediately.Aqueous NH4OH (7.3 M, 1 mL) was added dropwise to dissolve the precipitate.The resulting clear solution was cooled down to 5 °C.Glass slides were submerged in the cooled solution and aqueous D-glucose (0.35 g, 4 mL) was added.The mixture was stirred for 2 min at 5 °C, allowed to warm up to ambient temperature, heated to 40 °C and stirred for a further 10 min at this temperature.In the process, the yellow-green solution turned brown and a greenish coating deposited on the slides.
The slides were removed from the solution, washed with H2O, sonicated in H2O for 1 min at ambient temperature, washed again with H2O and dried in air for 2 hours.Atomic Force Microscopy.Atomic force microscopy (AFM) measurements were performed with a Multimode 8 system attached to a Bruker Nanoscope V electronics unit.Topographic data were acquired in Asyst Mode and Set point (proportional to the force exerted by the probe on the sample) was kept in automatic mode.All samples were analyzed using silicon nitride triangular levers with silicon oxide pyramidal tips (Bruker SNL-10, nominal spring constant = 0.35 nN•nm -1 ).Samples were glued to metallic discs with a two-component epoxy cement (Pattex Natural 27) and stored for 1 hour in air before the experiments.Images were captured at 20 × 20, 10 × 10, 2 × 2 and 1 × 1 μm to characterize each sample at different scales.The resolution was set to 512 × 512 pixels and the scan rate was adjusted between 0.1 and 0.5 Hz to optimize the images.The recorded data were analyzed with Bruker Nanoscope Analysis software.
Polymer Films.A solution of PBMA (10 mg mL -1 , MW = 337 × 10 3 ) and either 1 or 2 (3% w/w relative to PBMA) was deposited dropwise on either a glass or a quartz slide.The substrate was spun at 1500 rpm for 3 min with a Chemat Technologies KW-4A spin coater.The coated slides were stored under reduced pressure for 6 hours prior to any imaging and spectroscopic experiments.The same protocol was employed to deposit polymer films on glass slides pre-coated with silver nanoparticles.The thickness (ca.0.2 m) of the resulting films was measured with a Veeco Dektak Mechanical Profilometer.Fluorescence images of the substrates were recorded with a Leica SP5 confocal laser-scanning microscope.
. S7-S12) were recorded with a PicoQuant Fluotime 200 time-correlated single photon counting system, using pulsed laser excitation at 375 nm and a Picoquant's PMA 182-M single photon detector.The excitation laser worked at 10 MHz repetition rate and the photon counting frequency was kept always below 1%.Time-resolved emission signals were analyzed by fitting the convolution of the instrument's response function with a multiexponential decay model using the PicoQuant FluoFit 4.0 software.The time resolution of the system is approximately 100 ps.The number of exponentials in the model function and the corresponding goodness of the fit was judged by the distribution of residuals and the value of the Chi-square parameter.S1 M. Grigoras and N.-C.Antonoaia, Eur.Polym.J., 2005, 41, 1079-1089.S2 Y. Zhang, S. Swaminathan, S. Tang, J. Garcia-Amorós, M. Boulina, B. Captain, J. D. Baker, F. M. Raymo, J. Am.Chem.Soc., 2015, 137, DOI:10.1021/ja5125308.

Fig. S4 .
Fig. S4.Absorption spectrum of silver nanoparticles deposited on a quartz slide.

Fig. S6 .
Fig. S6.AFM images of silver nanoparticles deposited on a glass slide captured at increasing magnification (a  c).

Table S1 .
Fluorescence decay times for 1 after irradiation (λAc = 350 nm, 4.88 mW cm −2 , 10 min) and for 2 in MeCN solution and PBMA films (3% w/w) without and with silver nanoparticles.The values in parenthesis indicate the fractional amplitudes of the different positive