Alcohol-soluble bis(tpy)thiophenes: new building units for constitutional dynamic conjugated polyelectrolytes

Abstract

New building units (unimers) for metallo-supramolecular polymers 2,5-bis(2,2':6',2''-terpyridine-4'-yl)thiophene, M, and 5,5'-bis(2,2':6',2''-terpyridine-4'-yl)(2,2'-bithiophene), B, with ionic groups attached to thiophene rings are prepared by the modification of corresponding bromo-precursors and assembled with Zn(2+) and Fe(2+) ions into alcohol-soluble conjugated constitutional-dynamic polyelectrolytes (polyelectrolyte dynamers). Ionization of side groups only slightly affects the absorption spectra of unimers as well as dynamers but dramatically changes their solubility. Cyclic conformations of unimer molecules resulting from intramolecular interactions between tpy end-groups and cationic or polar (-CH2Br) side groups are proposed to explain the spectral conformity of the M- and B-type unimers and their dynamers and also inhibition of the ionization reaction with tpy end-groups. The absorption spectra and excitation profiles of Raman spectra show that mainly the red arm of the metal-to-ligand charge transfer band of Fe-dynamers is significantly contributed with transitions involving thiophene rings. The constitutional dynamics of Zn-dynamers is fast while that of Fe-dynamers is so slow that it allows effective separation of the dynamer to fractions in SEC columns. Electronic spectra and viscosity measurements proved that excess of Fe(2+) ions results in shortening of the dynamer chains and their end-capping by these ions.

Conjugated Metallo-Supramolecular Polymers Containing a Phosphole Unit

“…Optical and redox properties of the unimer TPT In order to have an understanding of the characteristics of this novel π-conjugated unimer TPT, we studied its optical and electrochemical properties. The UV/vis absorption spectrum in solution of TPT (Figure 1a) shows a band centered at 281 nm that is mainly contributed by transitions in tpy end-groups 45 and a band centered at λ abs = 481 nm that is contributed by HOMO to LUMO transitions that are spread over the unimer central block and adjacent central rings of tpy end-groups [20][21][22]24,42,45 (Figure 1b) shows a structured emission band centered at λ F = 603 nm. As expected, the presence of an extended π-conjugation in TPT induces a significant red-shift in the absorption and emission maxima compared to the corresponding bands of the central block without tpy end-groups (λ abs = 432 nm; λ F = 548 nm).…”

“…The UV/vis spectral changes (see Figures S7 and dependences in Figure 4) indicate three stages of assembling, which are usually observed for similar systems. 23,24…”

“…These features are typical of the prolongation of MSP chains. [22][23][24]54,55 The third stage of the assembly (r > 1) is characterized by a small change in the spectral pattern that can be attributed to end-capping of MSP chains with metal ions and/or equilibrium dissociation of longer chains to shorter ones induced by superfluous metal ions. 42,56,57 As indicated above, the Fe 2+ /TPT system behaves differently from the other ones: only a small red shift (+ 11 nm) and a continuous attenuation of the main optical band is observed if the value of r increases, but together with progressive development of the MLCT band.…”

“…The size exclusion chromatography (SEC) method can provide qualitative information on the constitutional dynamics of MSPs in the solvent used as a mobile phase. 24,59 If an MSP with fast establishing assembly equilibrium (fast constitutional dynamics) is analyzed by SEC, only a peak for the free unimer is observed due to the fast disassembly of MSP upon multiple dilution of the injected solution inside columns (injected 20 L, elution volume of ca 40 mL). However, if an MSP with slow constitutional dynamics is injected, its chains do not completely or substantially dissociate during the SEC analysis and an SEC record resembling the record of an oligomer or polymer is obtained, from which the average degree of polymerization can be calculated.…”

“…to the targeted metallo-polymer. For example, various conjugated MSPs have been prepared from linear unimers with oligophenylene [13][14][15] , oligofluorene [16][17][18] and oligothiophene [19][20][21][22][23][24] central blocks capped with tridentate 2,2':6',2''-terpyridine-4'yl end-groups assembled with metal ions such as Ru 2+ , Fe 2+ , Zn 2+ and Co 2+ . 11,12,25 In general, central blocks of these unimers are composed of -bonded highly aromatic rings, which doesn't lead to an efficient delocalization of -electrons along the whole molecule owing to the rather high autonomy of strongly aromatic systems.…”