Liquid crystalline 21,23-dithiaporphyrins

Abstract

Meso-substituted 21,23-dithiaporhyrins were synthesized that self-assemble into columnar liquid crystalline phases. Furthermore, the porphyrins possess absorption profiles that span from 400 nm to 800 nm, undergo two reversible electrochemical redox reactions at approximately 465 and 670 mV vs. ferrocene/ferricenium and are electrochromic. Thin films of these dithiaporhyrins of approximately 60 nm thickness were formed by spin-casting methods from chloroform and were subjected to impedance spectroscopy. The pristine films showed very low conductivity at open circuit potentials (undoped); however, electrochemically p-doping resulted in stable films with four orders of magnitude higher conductivity.

Pi-Extended Ethynyl 21,23-Dithiaporphyrins: A Synthesis and Comparative Study of Electrochemical, Optical, and Self-Assembling Properties

“…Typically, porphyrins with less than four meso -arylethynyl substituents are synthesized via reaction of TIPS-propynal and subsequent Sonogashira cross-couplings. ,− Dithiaporphyrin synthesis involves a synthetic route from 2,5-thiophene diols, − , shown in Scheme , prior to the final macrocyclic ring-closing step. This diol formation synthetic step permits a cleaner macrocyclization reaction, resulting in easier purification because scrambling is largely suppressed.…”

“…As such, the following derivatives were synthesized: one with a weakly electron-donating alkyl group and one with a strong electron-donating ether group. Scheme S1 (see Supporting Information (SI)) shows the synthetic details, which afforded the ethynyl precursors 1a and 1b that were previously reported. , Briefly, the synthesis of the strong electron-donating substituent begins by alkylating 4-bromophenol as described in our previous synthetic work , to obtain 1-bromo-4-(dodecyloxy)­benzene. The weakly electron-donating 1-bromo-4-dodecylbenzene was obtained by a Friedel–Crafts acylation of bromobenzene with dodecanoyl chloride followed by a Wolff–Kishner reduction .…”

“…For applications in organic photovoltaics, improved properties include the following: bathochromically shifted absorbance profile to harvest low energy photons; lowered oxidation potentials to become stronger donor materials; and an attempt to impart long-range ordering on these materials through liquid crystalline phases. Core-modified 21,23-dithiaporphyrins, for example, have shown enhanced visible light absorption and facile redox properties compared to their nitrogen counterparts. − Recently, porphyrins have appeared in the materials community as highly efficient, even world-leading, components in photovoltaic power conversion efficiencies. Many of the highest performance compounds employ the “donor–acceptor” or “push–pull” approach to porphyrins, which are achieved through two sequential Sonogashira cross-coupling reactions of ethynyl moieties carried out after the porphyrin ring-closing step. ,− Under standard porphyrin synthesis conditions involving an aryl-aldehyde and pyrrole in the presence of a Lewis acid, the yields are usually low, as such, there are practical motivations to avoid postporphyrin modifications.…”

Discotic Liquid Crystals

“…More exotic porphyrins were published by Sessler, prepared a cyclo[8]­pyrrole, which was nonmesomorphic, but showed broad Col h phases upon complexation of TNF, trinitrobenzene, trinitrotoluene, or picric acid . 21,23-Dithiaporphyrins with Col r and Col h phases, exhibiting electrochromic properties, were described by Bromby et al Thin films of these materials generated by spin-casting showed an increase of the conductivity by 4 orders of magnitude upon electrochemical p-doping, making them interesting candidates for organic photovoltaics.…”

Board‐like Fused‐Thiophene Liquid Crystals and their Benzene Analogs: Facile Synthesis, Self‐Assembly, p‐Type Semiconductivity, and Photoluminescence

“…[6] Oligothiophene derivatives end-capped with alkyl chains, show liquid crystalline properties, [7][8][9][10][11][12][13][14][15][16][17][18][19][20] and prefer to self-organize into supramolecular ordered layered structures:t hey display two-dimensional charge transport mobility comparable to inorganic semiconductors of amorphous and polycrystalline silicon, and have been investigated as active materials in organic field-effect transistors (OFET). [21][22][23][24][25] Discoticl iquid crystals (DLCs) [26][27][28][29] that contain afused-thiophene unit [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46] are also attractive candidates as novel organic semiconductors owing to their advantageous combination of the highly applicable and promising electronic properties of the thiophene moiety and the propensityo fD LCs to self-organize into ac olumnar mesophase for one-dimensional charget ransportp athways. [26] However,t he number of thiophene-containing DLCs is still limited compared with the numerousr od-like liquid crystalsi ncorporatin...…”