Photochemical transformations of 2,2′-(1,2-phenylenedivinylene)dipyrroles

Abstract

The photochemistry of 2,2'-(1,2-phenylenedivinylene)dipyrroles (4a,b) has been investigated under various conditions. After excitation of the starting material, an electron transfer followed by hydrogen transfer and radical combination occurs giving 2-[[1-(2H-pyrrol-2-ylidene)methinyl]-2-indanyl]pyrrole (14) as the intermediate. The intermediate could not be isolated, but trapped by nucleophiles, like methanol and diethylamine, giving as addition products, new functionalised indanylpyrroles (9). Irradiation of 4a in the presence of triethylamine afforded the indanylidene-pyrroles 8.

Very Efficient Generation of Quinone Methides through Excited State Intramolecular Proton Transfer to a Carbon Atom

“…[11] The most common acidic group in the ESIPT reactions is the phenolic OH or amine NH, whereas the basic site is usually a heteroatom such as pyridine nitrogen or carbonyl oxygen. [1] Although some examples are known wherein protonation of a carbon can compete with the protonation of heteroatoms, [12] ESIPT to carbon usually takes place with much lower quantum efficiency. [13][14][15][16][17][18][19] Consequently, it is often overlooked as a possible nonradiative relaxation pathway in biological molecules, [20] or as a viable synthetic route to quinone methides (QM).…”

“…[24] To date, several examples of ESIPT to carbon atoms of the aromatic ring have been described. [12][13][14][15][16][17][18][19][20] One prominent example is that of 1-naphthol (1). In S 1 , 1 becomes significantly more acidic (pK* a = 0.4), [13] and in addition to proton transfer (PT) to solvent, a solvent-assisted transfer of the OH proton to the carbon atom at position 5 of the ring takes place giving quinone methide (QM) 2 with a quantum efficiency of 0.11 (Reaction (1)).…”

Photochemical and Thermal Transformations of Thiophene o-Distyrylbenzene Analogues in Acidic Media

“…Our recent research on the intramolecular photochemical reactions of conjugated thiophene derivatives 1,2 continues the work on furan [3][4][5][6][7][8][9][10] and pyrrole [11][12][13][14][15][16] derivatives of o-divinylbenzenes. Dithiophene derivatives 1, 2 react differently 2 in comparison to previously studied difuran 3 8 and dipyrrole 4 12 derivatives ( Figure 1).…”

Synthesis and Photochemistry of β,β′‐Di(2‐furyl)‐Substituted o‐Divinylbenzenes: Intra‐ and/or Intermolecular Cycloaddition as an Effect of Annelation

“…Thus, b,b'-diphenyl-o-divinylbenzene, even at very low concentrations (< 10 À5 m), undergoes photodimerization to give products of structural type 8, [23][24][25] whereas in the crystal form [21] or adsorbed onto silica gel [25] it undergoes an intramolecular cycloaddition reaction to give a bicyclo[2.1.1]hexene derivative (structural type 6). Only a few examples of reactions that involve diheteroaryl-substituted o-divinylbenzene derivatives have been found: the photochemistry of o-phenylenedivinylenedipyrroles, [32][33][34] nitrogen analogues of 9, and the photochemistry of the diquinoxalinyl o-divinylbenzene derivative. [35] Whereas the dipyrrole derivative, after photoexcitation followed by electron and hydrogen transfer, undergoes ring closure to the indane derivative, which then reacts further with the starting compound to give dimeric products, the diquinoxaline derivative showed photostability in the crystalline state.…”