# Electronic Properties of Electron-Deficient Zn(II) Porphyrins for HBr Splitting
## 2 Experimental
### Photoelectrochemical Measurements  
Photoelectrochemical measurements were carried out on a PGSTAT 302N potentiostat in a three-electrode configuration, using SCE and Pt wire, respectively, as the reference and the counter electrode. A LOT-Oriel solar simulator, equipped with an AM 1.5 G filter, was used as the illumination source, and set to 0.1 W cm\({}^{-2}\) incident irradiance power by means of a Power Meter (Newport 1918-C). Current-voltage curves, recorded at 10 mV/s, were repeated by cycling the photoanodes until an overlapping response upon subsequent scans (stationary state) was achieved. Current-voltage curves under shuttered illumination were acquired by manually chopping the excitation source. Incident photon-to-current conversion efficiency (IPCE) was measured in a three-electrode configuration under the monochromatic illumination generated by an air-cooled Luxtel 175 W Xe lamp coupled to an Applied Photophysics monochromator. The resulting photocurrent, recorded at the constant potential of 0.7 V versus SCE, was measured by a PGSTAT 302N potentiostat. Unless otherwise stated, all the potential values are given versus the standard calomel electrode, SCE.  
Transient absorption spectroscopy (TAS) was performed with a previously described apparatus [22], using the 532 nm harmonic of a nanosecond Nd:YAG laser (Continuum Surelite II) and a monochromatic probe beam. Transient measurements on thin films were obtained by orienting the electrodes at an angle of approximately 45\({}^{\circ}\) with respect to the excitation, with a laser fluence of 3.3 mJ/cm\({}^{2}\)/pulse, and without pulsing the probe beam. The probe light which was transmitted by the sample was passed through a stack of two 532 nm notch filters to eliminate the scattered laser and focused into a second group of 150 lines/mm grating before reaching the photomultiplier biased at 470 V. Spectra on the ms/sub ms timescale were recorded with an oscilloscope input impedance of 1 M\(\Omega\) to pre-amplify the differential absorbance (\(\Delta\)A) traces, which were averaged over 100 shots to obtain a good Signal-to-Noise (S/N) ratio. Transient kinetics under electrochemical polarization were recorded with an EcoChemie PGSTAT302/N potentiostat, employing a platinum electrode as a counter electrode in a two-electrode configuration. The decay traces were fitted with a biexponential function in order to obtain a smooth curve to extract the half-life (\(\tau_{1/2}\)) of the process. The normalized kinetic decays at 0.7 V versus Pt were used for the calculation of the regeneration constant (k\({}_{\text{reg}}\)), in the presence of the Br\({}^{-}\) electrolyte (NaBr 0.3M, HBr 0.1M), from the recombination constant (k\({}_{\text{rec}}\)),computed from \(\tau_{1/2}\) of the charge separated state in the blank electrolyte (HClO\({}_{4}\)) (\(\mathrm{k_{rec}}=1/\tau_{1/2,blank}\)), according to the equations:  
\[\mathrm{k_{reg}}=\mathrm{k_{Br-}}-\mathrm{k_{rec}} \tag{1}\]  
\[\mathrm{k_{Br-}}=1/\tau_{1/2,Br-} \tag{2}\]  
where \(\tau_{1/2,Br-}\) is the half-life of the charge-separated state in the presence of Br\({}^{-}\).  
From the regeneration constant, regeneration efficiency related to Br\({}^{-}\) was estimated according to:  
\[\mathrm{\eta_{reg}}=\mathrm{k_{reg}/(k_{reg}+k_{rec})} \tag{3}\]  
Computational Chemistry  
All calculations were performed with Gaussian 09 [23]. Ground state structures of **1** and **2** were optimized at the B3 LYP/DGDZVP level [24] in vacuo. Singlet electronic transitions were computed on the optimized geometries at the TDDFT/B3 LYP/6-311G d,p level in toluene treated as a dielectric continuum (IEFPCM). Orbital isosurfaces were plotted with Gaussview 5 and electron/hole density maps were obtained with Multiwfn 3.3.9 [25] at an isolevel of 0.001.