C3¹-Selective substitution of cationic N-heteroaromatic groups into a 3-vinylated chlorophyll-a derivative

Abstract

A variety of N-heteroarenes were C31-selectively introduced for a chlorophyll-a derivative through a C–N+ bond by using iodine and a silver(i) salt.

Synthesis of Cationic Pyridinium‐(Bacterio)Chlorophyll Conjugates Bearing a Bacteriochlorin, Chlorin, or Porphyrin π‐Skeleton and their Photophysical and Electrochemical Properties

“…Specifically, the Qy(0,0) maxima were shifted from 665 ( Chl‐1 ) to 673 nm ( Chl‐2 ), and the red shift was estimated to be 180 cm –1 , while the main emission maxima were shifted from 671 ( Chl‐1 ) to 678 nm ( Chl‐2 ), and the red shift was 150 cm –1 (Table ). These bathochromic shifts are ascribable to the electron‐withdrawing cationic pyridinium substituent at the 3 1 ‐position on the electronic transition moment along the molecular y ‐axis, as detailed in our previous report…”

“…To investigate the effect of the pyridinium substituent to the core cyclic tetrapyrrole, we measured the visible absorption and fluorescence emission spectra of (B)Chl‐ a derivatives possessing a bacteriochlorin BChl‐1/2 , chlorin Chl‐1/2 or porphyrin π‐skeleton Por‐1/2 in CH 3 CN (Figure ). We previously reported that introduction of the pyridinium group into Chl‐ a derivative Chl‐1 possessing a chlorin π‐skeleton moved the redmost (Qy) absorption and main fluorescence emission maxima to longer wavelengths (Figure b/e) . Specifically, the Qy(0,0) maxima were shifted from 665 ( Chl‐1 ) to 673 nm ( Chl‐2 ), and the red shift was estimated to be 180 cm –1 , while the main emission maxima were shifted from 671 ( Chl‐1 ) to 678 nm ( Chl‐2 ), and the red shift was 150 cm –1 (Table ).…”

“…and an CH 3 CN solution of AgPF 6 (2.0 eq.) under nitrogen atmosphere . After being stirred at room temperature in the dark for 2 h, the reaction mixture was purified by flash column chromatography [CH 2 Cl 2 /CH 3 OH = 100:1–2(v/v)] and precipitation from CH 2 Cl 2 and hexane to give methyl 3‐deacetyl‐3‐(1‐pyridiniovinyl)pyrobacteriopheophorbide‐ a hexafluorophosphate ( BChl‐2 ) as a purple powder in 52 % yield [step (v)].…”

“…Absorption bands of photofunctional pigments in solar cells should cover a wide range of sun‐light to achieve a high power‐conversion efficiency . We recently reported the one‐pot selective introduction of a cationic pyridinium group into the 3‐vinyl group of a Chl‐ a derivative in an excellent yield to control the Qy band (Figure ) . The synthetic procedures were also applied to couple various nitrogen‐containing heterocyclic compounds such as quinoline, imidazole, and nicotinic acid derivatives, which enabled us to fine‐tune the wavelength and intensity of the Qy maxima.…”

Efficient Synthesis of Long‐wavelength Absorbing Cyanochlorophyll a Derivatives via Stereoselective Horner–Wadsworth–Emmons Reaction

“…It is well known that structural changes, induced by the peripheral substituents conjugated with the chlorin chromophore, remarkably affect the photophysical properties of these porphyrins, especially their electronic absorptions . Various long‐wavelength absorbing chlorins have been synthesized by introducing electron‐withdrawing groups including nitro, keto, carboxyl, pyridyl, quinolyl and cationic N ‐heteroaromatic groups, most of which are prepared from 3‐formyl chlorins via classical CC bond‐forming reactions such as the Wittig, Knoevenagel, Henry, Grignard, and the aldol and aldol‐like condensation reactions …”