Red light excitation: illuminating photocatalysis in a new spectrum

• Lucas Fortier,
• Corentin Lefebvre and
• Norbert Hoffmann

Beilstein J. Org. Chem. 2025, 21, 296–326, doi:10.3762/bjoc.21.22

• that the photocatalytic efficiency of these molecules does not necessarily rely on the presence of a central metal atom. Free-base porphyrins, in particular, have demonstrated significant potential in red-light-driven transformations due to their versatile photophysical properties. These metal-free

Advances in the use of metal-free tetrapyrrolic macrocycles as catalysts

• Mandeep K. Chahal

Beilstein J. Org. Chem. 2024, 20, 3085–3112, doi:10.3762/bjoc.20.257

• two macrocycles as metal-free catalysts. Keywords: calix[4]pyrroles; electrocatalysis; free-base porphyrins; organocatalysis; photocatalysis; tetrapyrrolic macrocycles; Introduction Tetrapyrrolic macrocycles are a class of cyclic compounds that contain four pyrrolic units in their ring. Examples of

• . Changes in the reduction or oxidation state can alter redox behavior, thereby affecting catalytic activity. For example, it has been reported that 2,3,5,7,8,10,12,13,15,17,18,20-dodecasubstituted free-base porphyrins and their mono/diprotonated derivatives are highly distorted with a good access to the

Unravelling a trichloroacetic acid-catalyzed cascade access to benzo[f]chromeno[2,3-h]quinoxalinoporphyrins

• Chandra Sekhar Tekuri,
• Pargat Singh and
• Mahendra Nath

Beilstein J. Org. Chem. 2023, 19, 1216–1224, doi:10.3762/bjoc.19.89

• ≈675 nm and 730 nm (Figure 5a). These newly synthesized free-base porphyrins displayed significant red-shifts in their emission spectra in comparison to meso-tetrakis(4-methylphenyl)porphyrin (TMPP; emission bands at ≈652 and 717 nm). Similarly, fluorescence spectra of zinc(II) benzo[f]chromeno[2,3-h

• -base porphyrins 9, 10 and 13 afforded zinc(II) benzo[f]chromeno[2,3-h]quinoxalinoporphyrins 14–16 in good yields (Scheme 1). The proposed mechanistic pathway for the formation of copper(II) benzo[f]chromeno[2,3-h]quinoxalinoporphyrins 3–8 under one-pot operation is presented in Figure 1. At the

• copper complexes of benzo[f]chromeno[2,3-h]quinoxalinoporphyrins 3–7 were converted to the corresponding free-base porphyrinoids 9–13 through a standard demetallation process using conc. H2SO4 in CHCl3 under cooling conditions (Scheme 1). On complexation with zinc by using Zn(OAc)2 in CHCl3/MeOH, free

CuAAC-inspired synthesis of 1,2,3-triazole-bridged porphyrin conjugates: an overview

• Dileep Kumar Singh

Beilstein J. Org. Chem. 2023, 19, 349–379, doi:10.3762/bjoc.19.29

• 6–10 in the presence of CuSO4·5H2O and ascorbic acid in DMF at 80 °C (Scheme 2). Further, the corresponding free-base porphyrins 11b–20b were obtained in good yields after demetallation of copper and zinc porphyrins under acidic conditions. Also, their zinc analogues 11c–15c were obtained by the

• treatment of free-base porphyrins with zinc acetate. The photophysical studies of these synthesized conjugates revealed that some of them show substantial intramolecular energy transfer between porphyrin and coumarin moieties. Similar to coumarins, synthetic and naturally occurring xanthones also possess

• -base porphyrins 23b–29b in good yields. In addition, their zinc analogues 23c–25c were also obtained in excellent yields by the reaction of free-base porphyrins with zinc acetate. The preliminary photophysical studies of the porphyrin-xanthone dyads show a bathochromic shift in the absorption and

Synthesis and spectroscopic properties of β-triazoloporphyrin–xanthone dyads

• Dileep Kumar Singh and
• Mahendra Nath

Beilstein J. Org. Chem. 2015, 11, 1434–1440, doi:10.3762/bjoc.11.155

• demetalation under acidic conditions to afford the corresponding free-base porphyrins in good to excellent yields. After successful spectroscopic characterization, these porphyrins have been evaluated for their photophysical properties. The preliminary results revealed a bathochromic shift in the UV–vis and

• ) derivatives 7a,c with conc. HCl at 25 °C and neutralization with 5% aq NaHCO3 afforded the corresponding free-base porphyrins 6b,e,h and 7b,d, respectively in 78–83% yields. In addition, the zinc porphyrins 6c,f,i and copper porphyrin 7e were prepared in 90–93% yields from free-base porphyrins 6b,e,h and 7d

• singlet of two protons at around δ −2.7 ppm was assigned for internal NH protons of the porphyrin core in the case of all the free-base porphyrins. In porphyrins 7a–d and 13a,b, a singlet for the methylene protons was observed between δ 5.76–5.82 ppm. Similarly, a singlet of three protons due to the

First synthesis of meso-substituted pyrrolo[1,2-a]quinoxalinoporphyrins

• Dileep Kumar Singh and
• Mahendra Nath

Beilstein J. Org. Chem. 2014, 10, 808–813, doi:10.3762/bjoc.10.76

• two weaker Q bands at ~553 and 594 nm. In comparison to the TPP and Zn–TPP, the UV–vis spectra of free-base porphyrins 4a–h and zinc porphyrins (5 and 6) were found to be red-sifted by 3 to 4 nm. The electronic absorption spectra of selected free-base porphyrins (4f, 4g, 4h and TPP) and zinc(II

• % yields via TFA-catalyzed Pictet–Spengler cyclization with aromatic aldehydes followed by in situ oxidation in the presence of KMnO4. These porphyrin architectures may be useful as potential candidates for various biological evaluations. (a) Electronic absorption spectra of free-base porphyrins 4f, 4g, 4h

Synthesis of meso-substituted dihydro-1,3-oxazinoporphyrins

• Satyasheel Sharma and
• Mahendra Nath

Beilstein J. Org. Chem. 2013, 9, 496–502, doi:10.3762/bjoc.9.53

• . Further, these free-base porphyrins were successfully converted to their zinc(II) analogues 10–13 by using Zn(OAc)2·2H2O as outlined in Scheme 1. In contrast, the synthesis of new dihydro-1,3-naphthoxazinoporphyrins 14 and 16 was achieved in 75–85% yields in a one-pot three-component Mannich type

• NMR, IR, mass and UV–vis data. The 1H NMR spectra of all the free-base porphyrins showed a singlet around δ −2.7 ppm corresponding to the internal NH protons. Iminoporphyrins 2 and 3 showed the OH and N=CH protons as singlets around 13.4 and 8.9 ppm, respectively. For the aminoporphyrins 4 and 5, the

• 648 nm. In contrast, the zinc(II) dihydro-1,3-oxazinoporphyrins showed the Soret band at 426 nm and two Q bands at ~555 and 597 nm. In addition, the newly prepared free-base porphyrins displayed typical emission bands at ~652 and 717 nm, whereas their zinc(II) analogues showed fluorescence bands near