Effect of substituents on redox, spectroscopic and structural properties of conjugated diaryltetrazines—a combined experimental and theoretical study

Abstract

Two series of new soluble conjugated compounds containing tetrazine central ring have been synthesized. The three-ring compounds have been synthesized by the reaction of aryl cyanide (where aryl = thienyl, alkylthienyl, phenyl or pyridyl) with hydrazine followed by oxidation of the intermediate product with diethyl azodicarboxylate. The five-ring compounds have been prepared using two pathways: (i) reaction of 5-cyano-2,2'-bithiophene (or its alkyl derivative) with hydrazine; (ii) via Suzuki or Stille coupling of 3,6-bis(5-bromo-2-thienyl)-1,2,4,5-tetrazine with a stannyl or boronate derivative of alkylthiophene. UV-vis spectroscopic properties of the synthesized compounds are strongly dependent on the nature of the aryl group, the position of the solubilizing substituent and the length of the molecule, showing the highest bathochromic shift (λ(max) > 440 nm) for five-ring compounds with alkyl groups attached to C(α) carbon in the terminal thienyl ring. An excellent linear correlation has been found for spectroscopically determined and theoretically calculated (TD-B3LYP/6-31G*) excitation energies. With the exception of dipyridyl derivative, the calculated lowest unoccupied molecular orbital (LUMO) level of the investigated molecules changes within a narrow range (from -2.63 to -2.41 eV), in line with the electrochemical data, which show a reversible reduction process with the redox potential varying from -1.23 V to -1.33 V (vs. Fc/Fc(+)). The electrochemically determined positions of the LUMO levels are consistently lower by 0.9 to 1.2 eV with respect to the calculated ones. All molecules readily crystallize. Single crystal studies of 3,6-bis(2,2'-bithien-5-yl)-1,2,4,5-tetrazine show that it crystallizes in a P2(1)/c space group whose structural arrangement is not very favorable to the charge carriers flow within the crystal. Powder diffraction studies of other derivatives have shown that their structural organization is sensitive to the position of the solubilizing substituent. In particular, the presence of alkyl groups attached to C(α) carbon in the terminal thienyl ring promotes the formation of a lamellar-type supramolecular organization.

Star‐Shaped Conjugated Molecules with Oxa‐ or Thiadiazole Bithiophene Side Arms

“…One should additionally note that the position of the π–π* band is also dependent on the number of alkyl solubilizing groups, being bathochromically shifted by 12 nm for the derivatives with two alkyl substituents in each arm. The same effect of alkyl substituents on molecular planarization (as evidenced from B3LYP/6‐31G* calculations) and on their increase in aromaticity (determined by the bond length alternation (BLA) parameter) was reported for penta‐ring linear compounds constituted of a central tetrazine, thiadiazole or oxadiazole electron accepting group symmetrically disubstituted with alkyl‐ or dialkylbithiophenes. As a result, weak positive inductive effect of alkyl substituents leads to lowering of the optical gap.…”

Symmetrically Disubstituted Bithiophene Derivatives of 1,3,4-Oxadiazole, 1,3,4-Thiadiazole, and 1,2,4-Triazole – Spectroscopic, Electrochemical, and Spectroelectrochemical Properties

“…1,16,17 The above outlined strategy can also be applied to the synthesis of molecules showing IP significantly higher than that of oligothiophenes. In such compounds a central strongly electron accepting unit of tetrazine- [18][19][20][21] , thiadiazole- 22,23 or oxadiazole-type bridges two bi-or terthiophene segments. 24 In this report we describe new five-ring donor-acceptor-donor Electrochemical determination of the redox properties of these new semiconductors is of crucial importance in view of the fact that some of them show strong electroluminescence and can be used as components of light emitting diodes with tunable colors .…”

Ultrahigh electron-deficient pyrrolo-acenaphtho-pyridazine-dione based donor–acceptor conjugated polymers for electrochromic applications

“…18 The subsequent bromination reaction with N-bromosuccinimide (NBS) in hot 1,2-dichloroethane, followed by an elimination process afforded dienophile intermediates 2-(2-alkyl)-1H-indeno[6,7,1-def ]isoquinoline-1,3(2H)diones 6-7. Following our established methodology, 17 the inverse electron demand Diels-Alder reaction between compounds 6 and 7 as the dienophile moiety, and thiophene-and furan-substituted 1,2,4,5-tetrazine derivatives 8-9 17,19 as the diene moiety in diphenyl ether occurred at 160 °C to afford monomers 10-12. Similar to our previous report, we observed the regio-selective Diels-Alder reaction occurring on the tetrazine moiety instead of occurring on the thiophene or furan moiety.…”