# Porphyrin and triphenylamine cores linked by a phenyl-azomethine bridge: Synthesis and characterization

Ibrahima Paka Manga, Mamadou Lo, Adji Fatou Fall Pouye, Christophe Gourlaouen, Henri-pierre Jacquot de Rouville, Abdoulaye Gassama, Jean Weiss

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Ibrahima Paka Manga, Mamadou Lo, Adji Fatou Fall Pouye, Christophe Gourlaouen, Henri-pierre Jacquot de Rouville, et al.. Porphyrin and triphenylamine cores linked by a phenyl-azomethine bridge: Synthesis and characterization. Journal of Porphyrins and Phthalocyanines, 2025, 30, pp.A-I. 10.1142/S1088424625500932. hal-05343129v2

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# Porphyrin and triphenylamine cores linked by a phenyl-azomethine bridge: Synthesis and characterization

Ibrahima Paka Manga<sup>a,*</sup>, Mamadou Lo<sup>a,*</sup>, Adji Fatou Fall Pouye<sup>a</sup>, Christophe Gourlaouen<sup>b</sup>, Henri-Pierre Jacquot de Rouville<sup>b</sup>, Abdoulaye Gassama<sup>a</sup> and Jean Weiss<sup>b</sup>

Received 24 June 2025

Accepted 12 August 2025

Dedicated to the memory of Prof. A. B. P. Lever (Barry)

**ABSTRACT:** Three meso-substituted Schiff base porphyrin derivatives were designed and synthesized by condensing the amine group of 5-(4-aminophenyl)-10,15,20-triphenylporphyrin (APTPP) with 4-formyltriphenylamine (2), 4,4'-diformyltriphenylamine (3), and 4,4',4"-triformylphenylamine (4). These molecules were developed for their potential interest in optoelectronic applications. The resulting compounds were thoroughly characterized using ¹H and ¹³C NMR, UV-vis spectroscopy, mass spectrometry, fluorescence, and cyclic voltammetry. Theoretical calculations were performed using DFT. The electrochemical properties were studied by cyclic voltammetry (CV).

**KEYWORDS:** porphyrin, triphenylamine, azomethine

## INTRODUCTION

Polyconjugated aromatic compounds have gathered significant interest from chemists and physicists over the years, particularly in the field of conductive materials. These intriguing chromophores form the basis of industrial dyes due to their extensive π-conjugation and function as semiconductors in electronic and optoelectronic devices, such as organic light-emitting diodes (OLEDs) [1], organic photovoltaic cells [2–4], as well as sensitizers in photodynamic therapy [5] or catalysts in numerous chemical reactions [6].

A significant portion of the polyconjugated aromatic compounds described in the literature is synthesized through coupling reactions that require palladium-based catalysts. The high cost of palladium continues to be a barrier to large-scale production. As a result, many researchers have developed new Schiff base-based chromophores featuring at least one imine bond, which is formed through the condensation reaction of an amine and aldehyde, releasing a water molecule as a by-product [7, 8].

Among the polyconjugated aromatic compounds, porphyrins have become one of the most commonly used building blocks. Porphyrins are macrocyclic compounds consisting of a central tetrapyrrolic ring, where methine bridges connect pyrrole units. They feature a 22-electron system, with 18 electrons involved in aromaticity, and exhibit a rigid, thermally stable structure. Porphyrins are excellent electron donors and acceptors and display strong absorption in the visible region. Their coordinating core can host nearly all metals from the periodic table

<footnote><sup>a</sup>Laboratoire de Chimie & Physique des Matériaux (LCPM), Université Assane Seck de Ziguinchor, BP 523 Ziguinchor, Sénégal</footnote>

<footnote><sup>b</sup>Institut de chimie de Strasbourg, Université de Strasbourg, UMR 7177 CNRS, Université de Strasbourg, 4 rue Blaise Pascal, 67000 Strasbourg, France</footnote>

<footnote>*Correspondence to: Mamadou Lo, e-mail: mlo@univ-zig.sn and Ibrahima Paka Manga, e-mail: i.manga4156@zig.univ.sn.</footnote>

<footnote>This is an Open Access article published by World Scientific Publishing Company. It is distributed under the terms of the Creative Commons Attribution 4.0 (CC BY) License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.</footnote>
and is known for its interesting optical and electronic properties [9]. Porphyrins are potentially helpful for various applications [10–14] and can be functionalized with substituents and groups that modify their physicochemical properties [15–17]. One of the most favoured donor moieties in polyconjugated derivatives is triphenylamine (TPA) and, more generally, any motif comprising a tertiary amine substituted with three aryl groups. Due to steric hindrance requirements, TPA possesses a propeller structure centered around its nitrogen atom. TPA is a chromophore, and in addition, it exhibits excellent electron-donating properties with good hole mobility and is used in Hole Transport Materials (HTMs) [1]. The TPA functional group possesses two fundamental properties in electrochemistry: the ease of oxidation of the nitrogen atom and the ability to effectively transport positive charges *via* radical cation species [18]. TPA derivatives are used in OLED devices [19, 20], solid-state dye-sensitized solar cells (DSSCs) [18, 21–23], perovskite solar cells (PSCs) [1, 24, 25] and in chemical sensors [26–29], among other applications.

To better understand how the number of porphyrin units affects the optoelectronic behavior of triphenylamine-based systems, we hypothesized that increasing the degree of substitution would influence the electronic communication between donor and acceptor units, thereby adjusting the photophysical and electrochemical properties of the resulting conjugates.

Subsequently, the synthesis of three new TPA derivatives, each linked to one, two, or three porphyrin units *via* imine bonds, is described. These new porphyrin derivatives were characterized by nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry. Additionally, their electronic properties were examined using UV-visible spectroscopy, fluorescence spectroscopy, and electrochemical studies, and correlated with Density Functional Theory (DFT) calculations.

# RESULTS AND DISCUSSION

## Synthesis of porphyrin

The target compounds **5**, **6**, and **7** were synthesized by forming an azomethine bond through the coupling of the amine group on porphyrin **1** with the aldehyde groups of compounds **2**, **3**, and **4**, respectively, under non-stoichiometric conditions (2.5*eq.*, 0.48*eq.*, and 0.3*eq.*, respectively). All coupling reactions were performed in toluene using a Dean-Stark setup. The formation of compound **5** was catalyzed by *p*-toluenesulfonic acid, whereas the synthesis of compounds **6** and **7** was catalyzed by scandium triflate (Scheme 1). To minimize hydrolysis of the azomethine bond during column purification, the silica gel was pre-treated with dichloromethane containing 10% (v/v) triethylamine. After

removing the solvent under reduced pressure, the neutralized silica gel was used for purifying the azomethine derivatives, ensuring their stability throughout the separation process. Subsequent recrystallization with suitable solvent systems yielded the final products as purple solids with yields of 75%, 13%, and 6% for compounds **5**, **6**, and **7**, respectively.

The chemical structures of the target molecules were characterized using instrumental techniques including ¹H NMR, ¹³C NMR, UV-vis spectroscopy, and high-resolution mass spectrometry (HRMS). The detailed spectra of the synthesized compounds are provided in the Supporting Information (Figs. S1–S10).

The formation of the azomethine bond between the porphyrin core and the triphenylamine moieties in compounds **5–7** was confirmed by ¹H NMR spectroscopy. For the monomeric compound **5**, a characteristic singlet of azomethine at δ 8.73 (s, 1H, CH=N) was observed. In the dimeric **6** and trimeric **7**, similar resonances appeared at δ 8.79 (s, 2H) and δ 8.80 (s, 3H), respectively. The presence of a single resonance in each case reflects their symmetric nature and indicates the formation of only one azomethine isomer. Additionally, the inner NH signals of the free-base porphyrin macrocycle were detected at δ -2.74, -2.73, and -2.70 for compounds **5**, **6**, and **7**, respectively, confirming the presence of non-metallated porphyrin units.

To further verify the monomeric, dimeric, and trimeric structures of the target compounds, HRMS (ESI+) analysis was performed. The HRMS (ESI+) spectra of compounds **5**, **6**, and **7** are provided in the Supporting Information. The HRMS (ESI+) spectrum of monomeric compound **5** showed two main molecular ion peaks corresponding to the mono-protonated and di-protonated species at m/z=885.3681 [M+H]⁺ and 443.1893 [M+2H]²⁺, respectively. Similarly, dimeric compound **6** exhibited molecular ion peaks at m/z=1524.6011 [M+H]⁺ and 762.8057 [M+2H]²⁺. For trimeric compound **7**, the HRMS (ESI+) spectra indicated the presence of mono-, di-, and tri-protonated species with molecular ion peaks at m/z=2163.8540 [M+H]⁺, 1082.4339 [M+2H]²⁺, and 721.9605 [M+3H]³⁺, respectively. These findings support the proposed monomeric, dimeric, and trimeric structures based on the expected molecular weights and charge states.

## Photophysical properties

To evaluate the effect of azomethine linkage on the electronic properties of the synthesized porphyrins, the UV-visible absorption spectra of compounds **5**, **6**, and **7** were examined in dichloroethane solutions and compared to that of the reference aminoporphyrin **1** (Fig. 1). The related spectral data are summarized in Table 1.

The three new porphyrins **5**, **6**, and **7** display four leading bands typical of a free base porphyrin in the
<figure><img src="image_4.png" /><figcaption>**Scheme 1.** Synthesis of novel TPA-porphyrin compounds 5, 6 and 7.</figcaption></figure>

<figure><img src="image_5.png" /><figcaption>**Fig. 1.** UV-visible Spectrum of compounds 5, 6 and 7 in dichloroethane.</figcaption></figure>

<table><caption>**Table 1.** UV-visible Absorption and Emission data ($\lambda_{ex}$=516 nm) for APTPP (1) and compounds 5–7 in dichloroethane.</caption><thead><tr><th>Compounds</th><th>Soret Band (nm)</th><th>Q Bands (nm)</th><th>λ<sub>em</sub> (nm)</th></tr></thead><tbody><tr><td>APTPP (1)</td><td>420</td><td>517, 554, 593, 649</td><td>652</td></tr><tr><td>5</td><td>421</td><td>516, 552, 591, 647</td><td>649</td></tr><tr><td>6</td><td>420</td><td>516, 552, 591, 647</td><td>650</td></tr><tr><td>7</td><td>421</td><td>516, 552, 591, 647</td><td>649</td></tr></tbody></table>

UV-visible spectrum: an influential band called the Soret band and four weaker Q bands. These absorption bands come from $\pi-\pi^*$ transitions within the porphyrin's aromatic system. The Soret band, which indicates the aromaticity of the porphyrin core, is minimally affected by
structural modifications. In contrast, the Q bands are more responsive to the type and position of the substituents attached to the ring. Significantly, the band from TPA is obscured by the intense absorption of the Soret band.

The UV-visible spectra of these three new compounds show profiles very similar to that of aminoporphyrin **1**. These slight variations suggest that the azomethine linkage does not promote efficient electronic communication between the porphyrin core and TPA group. As a result, this linkage does not allow conjugation between the different segments. This disruption could be due to the non-coplanarity of the two peripheral phenyl groups involved in forming the azomethine linkage. Additionally, it may indicate that the TPA group is far enough from the porphyrinic core to have a negligible effect on its electronic distribution.

The photoluminescent properties of the compounds were also studied through fluorescence in dichloroethane solution, excited at a wavelength $λ_{ex}=516$ nm. The fluorescence emission spectra of porphyrins **5, 6**, and **7**, as well as aminoporphyrin **1**, are shown in Fig. 2. Upon excitation, the emission maxima were observed between 649 and 652 nm, mainly due to the porphyrin unit.

A slight hypochromic shift (between 2 and 3 nm) is observed in compounds **5, 6**, and **7** compared to aminoporphyrin **1**. This shift indicates that the azomethine linkage does not significantly influence the fluorescent nature of the porphyrin unit, unlike the amino group in compound **1**, whose donor effect is more pronounced than that of the TPA moiety linked *via* an azomethine bond. These findings confirm the absence of extended electronic conjugation between the TPA group and the porphyrin core. The emission remains primarily on the porphyrin unit, and the TPA groups do not majorly interfere with the main electronic transitions. The reduced emission intensity seen in compounds **5, 6**, and **7** could be due to complex interactions impacting electronic delocalization. This decrease might also stem from enhanced internal quenching mechanisms or more efficient non-radiative energy transfer processes in the TPA-modified compounds.

<figure><img src="image_6.png" /><figcaption>**Fig. 2.** Emission spectra of compounds **5, 6**, and **7** in dichloroethane.</figcaption></figure>

## Electrochemical redox properties

The three new porphyrins were characterized using cyclic voltammetry. This analysis is important for understanding how the number of azomethine bonds affects redox properties, especially within the TPA group. TPAs are effective electron donors and hole conductors due to their low ionization potential. The redox activities of compounds **5, 6**, and **7** were examined in the oxidation region through cyclic voltammetry (CV). Electrochemical testing was carried out in a solution containing 0.1 mol·L⁻¹ *n*-tetrabutylammonium hexafluorophosphate (TBAPF₆) as the supporting electrolyte in dichloroethane. The potentials are measured against an AgCl/Ag reference electrode. The scan rate was set at 100 mV·s⁻¹. The cyclic voltammetry profiles of compounds **5, 6**, and **7** are shown in Fig. 3, with the data summarized in Table 2.

The CV curves of compounds **5** and **6** display similar patterns. Both compounds show three oxidation peaks and two reduction peaks each. The oxidation peaks related to TPA correspond to the loss of an electron from the central nitrogen atom of TPA, resulting in a cation radical. The irreversibility of these systems is likely due to the absence of a substituent at the *para*-position of the TPA phenyl groups. Specifically, the unprotected

<figure><img src="image_7.png" /><figcaption>**Fig. 3.** Electrochemical cyclic voltammetry (WE: Pt, CE: Pt, Ref: Ag wire, 100 mV·s⁻¹) of compounds **5, 6**, and **7** in dichloroethane solution (c = 1 × 10⁻³ mol·L⁻¹ with TBAPF₆ as supporting electrolyte).</figcaption></figure>

<table><caption>**Table 2.** Measured redox potentials (V vs Ag⁺/Ag) of compounds **5, 6** and **7** by CV.</caption><thead><tr><th rowspan="2">Compound</th><th colspan="5">Oxydation<br>(V vs Ag⁺/Ag)</th></tr><tr><th>E<sub>p,c1</sub></th><th>E<sub>p,c2</sub></th><th>E<sub>p,c3</sub></th><th>E<sub>p,a1</sub></th><th>E<sub>p,a2</sub></th></tr></thead><tbody><tr><td>5</td><td>+0,966</td><td>+1,066</td><td>+1,317</td><td>+1,226</td><td>+0,925</td></tr><tr><td>6</td><td>+0,979</td><td>+1,114</td><td>+1,319</td><td>+1,224</td><td>+0,917</td></tr><tr><td>7</td><td>+0,989</td><td>+1,329</td><td>—</td><td>+1,213</td><td>+0,904</td></tr></tbody></table>
4'-position of the phenyl leads to the dimerization of the cation radical [30–37].

In contrast, compound **7**, where the *para* positions of the TPA phenyls are substituted, exhibits two fully reversible systems. The reversibility of these systems corresponds to the successive loss of electrons from the central nitrogen lone pair of TPA, leading to the formation of a cation radical, and the subsequent loss of an electron from the cation radical, resulting in a dication.

Therefore, comparing the potentials of the first and last oxidations of the three compounds showed nearly identical values. These findings support the UV-visible and fluorescence data, indicating that *para*-substitution of TPA with one or more porphyrin rings through an azomethine bond has little effect on the electronic properties of the new chromophore.

## DFT (Density Functional Theory) study

Density Functional Theory (DFT) calculations were performed to verify the electronic properties in compounds **5, 6**, and **7**. Specifically, calculations aimed to determine the Highest Occupied Molecular Orbital (HOMO) and the Lowest Unoccupied Molecular Orbital (LUMO).

The summarized data are listed in Table 3. The HOMO and LUMO molecular orbitals of the studied compounds are shown in Fig. 4. In all structures, the HOMO is mainly localized on the TPA core, and the LUMO is a $\pi^*$ orbital on one of the porphyrin cores.

It has been observed that the addition of porphyrin groups in the *para* positions of the TPA phenyls *via* azomethine linkages further stabilized the LUMOs, lowering their energies: -3.00eV (**5**), -3.02eV (**6**), and -3.03eV

<table><caption>**Table 3.** HOMO and LUMO Energy levels for compounds **1, 5, 6** and **7**.</caption><thead><tr><th></th><th>1</th><th>TPA</th><th>2</th><th>3</th><th>4</th><th>5</th><th>6</th><th>7</th></tr></thead><tbody><tr><td>LUMO+1</td><td>-2.946</td><td>-0.884</td><td>-1.144</td><td>-1.962</td><td>-2.484</td><td>-2.976</td><td>-3.016</td><td>-3.025</td></tr><tr><td>LUMO</td><td>-2.980</td><td>-0.998</td><td>-2.093</td><td>-2.431</td><td>-2.508</td><td>-3.007</td><td>-3.024</td><td>-3.030</td></tr><tr><td>HOMO</td><td>-5.655</td><td>-5.555</td><td>-5.829</td><td>-6.011</td><td>-6.148</td><td>-5.639</td><td>-5.693</td><td>-5.719</td></tr><tr><td>HOMO-1</td><td>-6.024</td><td>-7.246</td><td>-7.360</td><td>-7.476</td><td>-7.555</td><td>-5.771</td><td>-5.765</td><td>-5.770</td></tr></tbody></table>

Orbital energies in eV.

<figure><img src="image_8.png" /><figcaption>**Fig. 4.** Frontier orbitals for compounds **5, 6** and **7**.</figcaption></figure>
(7) compared to -2.98 eV for precursor 1. This suggests a slight enhancement of the electron-accepting ability. Conversely, the impact on the HOMO levels is more moderate, retaining some donor capability while slightly increasing the stability relative to TPA. This accounts for the experimentally observed increase in the first oxidation potential from 5 to 7, while the stabilization of the LUMO corresponds to the decrease in the reduction potential.

The energy gap between the LUMO and HOMO levels increased slightly as the number of azomethine linkages and porphyrin groups around the TPA core grew: +2.632 eV (5), +2.669 eV (6), and +2.689 eV (7). This gap is essential for understanding the electronic properties of the compounds. It indicates an increase in stability and a decrease in reactivity for compounds 5, 6, and 7. However, these results suggest that porphyrin 1 ($ΔE$=2.765 eV) remains more stable and therefore less reactive than these compounds.

Additionally, it is essential to note that the charge separation mechanism heavily depends on the spatial distribution of the HOMO and LUMO densities, as it is closely related to electron injection. Typically, it is assumed that when compounds are excited, the first excitation involves an electron transfer from the HOMO localized on the donor part, and the LUMO is mainly localized on the acceptor part. As already mentioned and shown in Fig. 3, for all compounds, this transition primarily corresponds to charge transfer from the TPA core to one of the porphyrin moieties.

These results align with spectroscopic observations, indicating that modification through porphyrin groups and azomethine linkages improves electronic stability without significantly reducing the electron-donating ability of the TPA moiety.

# EXPERIMENTAL

## Materials and instruments

The solvents used for the reactions were distilled from sodium/benzophenone or calcium hydride to ensure purity. Analytical thin-layer chromatography (TLC) was performed on silica gel 60 $F_{254}$ (Merck), and column chromatography was performed using silica gel or alumina from Merck (silica gel 60, 0.04–0.063 µm or aluminum oxide 90 standardized). ¹H NMR and ¹³C NMR spectra were recorded using Bruker Avance spectrometers operating at 300 or 500 MHz. Chemical shifts are reported in ppm relative to the residual solvent peak, which was used as the reference value for ¹H NMR: $CDCl_3$=7.26 ppm. The data were presented in the following format: chemical shift, multiplicity (s=singlet, d=doublet, t=triplet, q=quadruplet, h=heptuplet, m=multiplet), coupling constant (J/Hz), and integration. High-resolution mass

spectrometry (HRMS) data were acquired using a microTOF II spectrometer equipped with an orthogonal electrospray ionization (ESI) interface. UV-vis absorption spectra were recorded using an Agilent 8453 spectrometer (Agilent Technologies) in dichloroethane.

## Electrochemical methods

The electrochemical experiments were performed using a Biologic SP150 potentiostat. Cyclic Voltammetry experiments were performed using a Pt working electrode (0.071 cm²). The electrode surface was polished routinely with a 0.05 µm alumina-water slurry on a felt surface immediately before use. The counter electrode was a Pt coil and the reference electrode was an Ag wire. Samples were prepared in $C_2H_4Cl_2$ (Aldrich, anhydrous, 99.8%) using 0.1 mol.L⁻¹ tetrabutylammonium hexafluorophosphate (TBAPF₆, Sigma Aldrich, +99%) as the supporting electrolyte. All cyclic voltammograms were recorded at a scan rate of 100 mV s⁻¹.

## Computational details

All calculations were performed using ADF 2019 [38, 39] at the DFT level with the B3LYP functional [40] and dispersion corrections [41] included via Grimme corrections. All atoms were described using the DZP basis set [42]. The solvent dichloroethane was modeled with a PCM [43]. All structures were fully optimized.

## Synthesis of precursors

The compounds listed below were synthesized using previously reported procedures: 4-(4-aminophenyl)-10,15,20-triphenylporphyrin (1) [44, 45], 4-formyltriphenylamine (2), 4,4'-diformyltriphenylamine (3), and 4,4',4"-triformylphenylamine (4) [46].

## Synthesis of porphyrins

### Synthesis of iminoporphyrin (5)

In Dean-Stark setup, porphyrin 1 (50 mg, 0.079 mmol) and 4-formyltriphenylamine (2) (55 mg, 0.201 mmol) were dissolved in toluene (10 mL). p-Toluenesulfonic acid (2 mg) was added to the reaction mixture under argon atmosphere. The flask was then refluxed under continuous stirring. The reaction progress was monitored by TLC. Once the reaction was complete, the reaction mixture was poured into water and the organic phase was extracted with $CH_2Cl_2$. The organic phase layer was dried over $Na_2SO_4$ and the solvent was removed using a rotary evaporator. The crude product was subjected to column chromatography on neutralized silica gel (pretreated with dichloromethane containing 10% v/v triethylamine) using a mixture of ($CH_2Cl_2$/Cyclohexane, 3:7) as the eluent. The product was purified by recrystallization from
a CH₂Cl₂/MeOH mixture, yielding a purple solid (52.3 mg, 75% yield). UV-vis (C₂H₄Cl₂): λmax, nm (log ε) 421 (5.29), 516 (4.00), 552 (3.73), 591 (3.44), 647 (3.43). ¹H NMR (500 MHz; CDCl₃): δ, ppm -2.74 (s, 2H, pyrrole-NH), 7.15 (t, J = 7.4 Hz, 2H, Ph), 7.19 (d, J = 8.4 Hz, 2H), 7.23 (d, J = 7.8 Hz, 4H), 7.36 (t, J = 7.7 Hz, 4H), 7.60 (d, J = 7.9 Hz, 2H, Ph), 7.82 – 7.73 (m, 9H, Ph), 7.91 (d, J = 8.4 Hz, 2H, Ph), 8.24 (d, J = 7.2 Hz, 8H, Ph), 8.73 (s, 1H, N=CH), 8.88 (d, J = 9.8 Hz, 6H, pyrrole-H), 8.94 (d, J = 3.7 Hz, 2H, pyrrole-H). ¹³C NMR (126 MHz; CDCl₃): δ, ppm 119.47, 120.29, 121.62, 124.29, 125.71, 126.83, 127.85, 129.69, 130.26, 134.71, 135.58, 142.30, 147.06, 152.03, 160.27. MS (ESI-HR): *m/z* 885.3681 (calcd for [M + H]⁺ 885.3700); *m/z* 443.1886 (calcd for [M + 2H]²⁺ 443.1893).

## Synthesis of iminoporphyrin (6)

In the Dean-Stark setup, porphyrin **1** (130 mg, 0.206 mmol) and 4,4'-diformyltriphenylamine (**3**) (30 mg, 0.099 mmol) were mixed in toluene (20 mL). Scandium triflate (1.1 mg) was added under an argon atmosphere, and the mixture was heated under reflux for four days. Upon completion of the reaction, the mixture was poured into water and the organic phase was extracted with CH₂Cl₂. The organic layer was dried over Na₂SO₄ and the solvent was removed using a rotary evaporator. The crude product was purified by silica gel column chromatography. The silica gel was pretreated with dichloromethane containing 10% v/v triethylamine, and a solvent system of CH₂Cl₂/AcOEt/Cyclohexane (4:1:6) was used as the eluent. This process effectively removed a significant portion of the unwanted by-products. The desired compound **6** was obtained after several recrystallizations from a CHCl₃/MeOH mixture, yielding a purple solid (19.2 mg, 13%). UV-vis (C₂H₄Cl₂): λmax, nm (log ε) 420 (5.35), 516 (4.06), 552 (3.73), 591 (3.32), 646 (3.41). ¹H NMR (300 MHz; CDCl₃): δ, ppm -2.73 (s, 4H, pyrrole-NH), 7.37–7.29 (m, 7H, Ph), 7.48–7.40 (m, 2H, Ph), 7.62 (m, 4H, Ph), 7.81–7.72 (m, 18H, Ph), 8.01 (d, 4H, Ph), 8.29–8.21 (m, 16H, Ph), 8.79 (s, 2H, N=CH), 8.88 (d, J=9.0 Hz, 12H, pyrrole-H), 8.94 (d, J=4.8 Hz, 4H, pyrrole-H). MS (ESI-HR): *m/z* 1524.612318 (calcd for [M + H]⁺ 1524.601156); *m/z* 762.8098 (calcd for [M + 2H]²⁺: 762.8058).

## Synthesis of iminoporphyrin (7)

In the Dean-Stark setup, porphyrin **1** (245.3 mg, 0.389 mmol) and 4,4',4"-triformyltriphenylamine (**4**) (30 mg, 0.125 mmol) were dissolved in toluene (20 mL). Scandium triflate (10 mg) was added under an argon atmosphere, and the mixture was heated under reflux for one week. Upon completion, the reaction mixture was poured into water and the organic phase was extracted with CH₂Cl₂. The organic layer was dried over Na₂SO₄ and the solvent was removed using a rotary evaporator.

The crude product was subjected to column chromatography using neutralized silica gel pretreated with dichloromethane containing 10% v/v triethylamine. A CH₂Cl₂/AcOEt/Cyclohexane (4:1:10) solvent system was used as the eluent to separate the mixture. Further purification was achieved through several recrystallizations from CH₂Cl₂/EtOH mixture. The final product was obtained as a purple solid (15.26 mg, 6% yield). UV-vis (C₂H₄Cl₂): λmax, nm (log ε) 421 (5.35), 516 (4.06), 552 (3.75), 591 (3.38), 646 (3.46). ¹H NMR (500 MHz; CDCl₃): δ, ppm -2.70 (s, 6H, pyrrole-NH), 7.43 (d, J=8.2 Hz, 6H, Ph), 7.66 (d, J=8.0 Hz, 6H, Ph), 7.77 (q, J=7.2, 6.5 Hz, 27H, Ph), 8.09 (d, J=8.3 Hz, 6H, Ph), 8.32–8.23 (m, 24H, Ph), 8.84 (s, 3H, N=CH), 8.91 (d, J=17.7 Hz, 18H, pyrrole-H), 8.98 (d, J=4.8 Hz, 6H, pyrrole-H). ¹³C NMR (126 MHz; CDCl₃): δ, ppm 119.51, 119.90, 120.31, 120.33, 124.77, 126.85, 127.88, 130.61, 132.20, 134.72, 135.65, 140.00, 142.28, 142.31, 149.67, 151.72, 159.89. MS (ESI-HR): *m/z* 2164.8546 (calcd for [M + H]⁺ 2163.8540); *m/z* 1082.4309 (calcd for [M + 2H]²⁺ 1082.4339); *m/z* 721.9564 (calcd for [M + 3H]³⁺ 721.9605).

## CONCLUSION

In this study, three novel porphyrin-based derivatives (APTPPs), which include one, two, or three porphyrin cores linked to triphenylamine (TPA) units *via* phenyl-azomethine bridges, were synthesized through Schiff base condensation. Structural modifications at the *meso* position of the porphyrin in compounds **5**, **6**, and **7** had little impact on their optical properties, indicating limited electronic coupling between the TPA and porphyrin parts across the azomethine linker. In contrast, electrochemical analysis showed different redox behaviors, with compound **7** demonstrating increased reversibility, likely due to the specific features of its TPA substituent. DFT calculations supported these results, revealing improved electronic stability while maintaining the donor properties of the TPA units [47].

The weak conjugation between the porphyrin and TPA segments provides valuable functional features to these scaffolds. Indeed, their ambipolar nature makes them promising candidates for applications in organic field-effect transistors (OFETs), as they can combine electron transport through the porphyrin core and hole conduction *via* TPA units. Furthermore, their potential as efficient hole transport materials (HTMs) aligns with the increasing demand in perovskite solar cell technologies [48], an area where our laboratory has developed recognized expertise [49]. These findings open new avenues for designing multifunctional molecular materials for optoelectronic devices.

## Acknowledgments

We gratefully acknowledge the French Cooperation Agency in Senegal for financial support.
## Supporting information

Additional data are included in the supplementary material, which is available free of charge online at http://www.worldscientific.com/doi/suppl/10.1142/S1088424625500932.

## ORCID

Mamadou Lo

https://orcid.org/0000-0001-5251-8221

Christophe Gourlaouen

https://orcid.org/0000-0002-2409-2849

Henri-Pierre Jacquot de Rouville

https://orcid.org/0000-0002-9508-6446

Jean Weiss

https://orcid.org/0000-0001-7753-8958

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