Tuning photochemical properties of phosphorus(V) porphyrins photosensitizers

Photosensitizing and emission properties of P(v) porphyrins were studied. The nature of the axial ligands, occupying the apical position on the P centre adopting an octahedral coordination geometry, strongly influences singlet oxygen generation and charge transfer and allows switching between the two processes.


Experimental section
Page S3 Figure S1 Experimental setups for SO measurements in organic (left) and aqueous (right) media.
Page S8 Table 1 Stokes shifts and emission maxima of P(V) porphyrins. Page S11 Table 2 Quantum yields of S 1 -S 0 , S 1 -CT and S 1 -T 1 processes calculated from transient absorption experiments.
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Page S22 Figure S22 Normalized UV-Vis spectra of compounds 3a-5a in water.
Page S23 Figure S23 Normalized UV-Vis spectra of compounds 3b-5b in water.
Page S23 Figure  Page S30

Figure S35
Transient absorption spectra of complexes 4a and 5a Page S31 Intramolecular energy transitions without CT state for compounds 2, 3 and 5.
Page S32 Intramolecular energy transitions with CT state for compounds 4.
Page S33 Calculated transient absorption spectra data for complexes 2-5.
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Figure S36
Calculated molecular orbitals of 2a. Figure S37 Calculated molecular orbitals of 3a.

Page S35
Page S35 Figure S38 Calculated molecular orbitals of 4a.
Page S35 Figure S39 Calculated molecular orbitals of 5a.
Page S35 Figure S40 Calculated molecular orbitals of 2b Page S36 Figure S41 Calculated molecular orbitals of 3b Page S36 Figure S42 Calculated molecular orbitals of 4b Page S36 Figure S43 Calculated molecular orbitals of 5b Page S36

References
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Singlet oxygen and fluorescence experiments.
CHCl 3 was distilled over CaH 2 ; DMSO was frozen in a fridge (+4 °C), liquid phase was removed and residual solid was melted back; water was distilled with a standard distiller.
The photoluminescence spectra (λ ex = 550 nm) at 25 °C were recorded in quartz cells on a Horiba Scientific Flourolog spectrofluorimeter. Fluorescence quantum yields (Φ F ) were determined by a comparative method using Eq. (1): where Ф St F is fluorescence quantum yield of the standard, F and F St areas under the fluorescence emission peaks of the samples and the standard, respectively; A and A St are absorptions of the sample and the standard at the excitation wavelengths, respectively; n 2 and n 2 st are the refractive indices of solvents used for the sample and the standard, respectively. 1a in toluene (Φ F = 0.11) 3 was used as a standard.
A special experimental setup was constructed for singlet oxygen quantum yield determination experiments. Two modifications of it was used for organic and aqueous media.

Figure S1
Experimental setups for SO measurements in organic (left) and aqueous (right) media.
In case of organic solvents and DPBF as a singlet oxygen sensitive trap (Fig. 2, Fig. S30-S31), a Xenon lamp (HPX-2000, Ocean Optics), equipped with a narrow green filter (transmission maximum at 547 nm) was used for irradiation of the sample. A halogen lamp, equipped with an attenuator, (DH-2000, Ocean Optics) and a detector (in absorption mode) was installed orthogonally. Absorption spectra were registered every 2 sec. 1a in chloroform (Φ Δ = 0.50) 4 was used as a reference. In case of aqueous solutions and SOSG as a singlet oxygen S9 sensitive trap (Fig. 2), a violet semi-conducting laser (405 nm, STAR405F10, Roithner Laser Technik) was used for irradiation of the sample. The detector was switched to emission mode and connected orthogonally. Emission spectra were registered every 5 sec. 5,10,15,20-tetra(4sulfonatophenyl)-porphyrin in water (Φ Δ = 0.64) 5  The solution of investigated porphyrin mixed with DPBF has an overlapped spectrum ( Fig. 2) -Soret-band and DPBF-band are located in the same area. The exception is complex 2a: two individual peaks are observed (Fig. S30), since Soret-band undergoes significant bathochromic shift after complexation with phosphorus. Free-base TPP 1a was used as a standard with known quantum yield of singlet oxygen generation. Porphyrins were irradiated into Q-bands area with Xenon lamp equipped with narrow filter (547 nm). This region also avoids direct influence to DPBF and its photodegradation. 7 Moreover, in chloroform experiments, negative factors of its irradiation and further formation of phosgene and hydrochloric acid were avoided.
In case of aqueous solution, it is not possible to use previous scheme of the setup anymore, since SOSG-EP emits at 530 nm. Thus, samples in water were irradiated with violet laser 405 nm. Fluorescence of SOSG-EP was registered and used for further calculations (Fig. 2). Using described methods and procedures, values of singlet oxygen generation quantum yields for eight S10 different P(V) porphyrins are calculated and given in the table 1. Since complexes 2 hydrolyze in the presence of moisture they were not involved into investigations in distilled water.

Transient absorption spectroscopy experiments.
Transient absorption spectra were measured by the femtosecond pump to supercontinuum probe setup. The output of a Ti: sapphire oscillator (800 nm, 80 MHz, 80 fs, «Tsunami», «Spectra-Physics», USA) was amplified by a regenerative amplifier system («Spitfire», «Spectra-Physics», USA) at the repeating rate of 1 KHz. Frequency control of laser pulses was produced by regular device synchronization and control amplifier SDG II Spitfire 9132, manufactured by Spectra-physics (USA). The device allowed to change the pulse repetition frequency of the amplifier output from 0 to 1000 Hz. The amplified pulses were split into two beams. One of the beams was directed into a noncollinearly phase-matched optical parametric amplifier. The gauss pulses of 20 fs, 30 nJ at 620 nm were used as a pump. The second beam was focused onto a thin quartz cell with water to generate supercontinuum probe pulses. The pump and probe pulses were time-delayed with respect to each other using a computer-controlled delay stage. They were then attenuated, recombined, and focused onto the sample cell. The pump and probe light spots had the diameters of 300 and 120 µm, respectively.
Experiments were carried out at 278 K in acetonitrile. The pump pulse operation frequency was 60 Hz, which is sufficiently low to exclude permanent bleaching of the sample due to photochemical processes in the sample. The relative polarizations of pump and probe beams were adjusted to 54.7° (magic angle) or in parallel and perpendicular polarizations, where indicated. After the sample, the supercontinuum was dispersed by a polychromator («Acton SP-300») and detected by CCD camera («Roper Scientific SPEC-10»). Transient spectra of absorbance changes ∆A (t, λ) were recorded over the range of 380-800 nm. The measured spectra were corrected for group delay dispersion of the supercontinuum using the procedure described previously. 8

Figure S22
Normalized UV-Vis spectra of compounds 3a-5a in water.

Figure S23
Normalized UV-Vis spectra of compounds 3b-5b in water.

Figure S30
Degradation of DPBF in the chloroform solution of 2a.

Intramolecular energy transitions without CT state for compounds 2, 3 and 5.
Kinetics of the state population.
We neglect the transition of T 1 à S 0 suggesting that it is slow.