Synthesis and thermoelectric properties of 2- and 2, 8-substituted tetrathiotetracenes. Issue 13 (16th March 2018)

• Record Type: Journal Article
• Authors: Garrett, Mary Robert; Durán-Peña, María Jesús; Lewis, William; Pudzs, Kaspars; Užulis, Jānis; Mihailovs, Igors; Tyril, Björk; Shine, Jonathan; Smith, Emily F.; Rutkis, Martins; Woodward, Simon
• Is Part Of: Journal of materials chemistry. Volume 6:Issue 13(2018)
• Page Start: 3403
• Page End: 3409
• Publication Date: 2018-03-16
• Subjects: Materials -- Periodicals; Chemistry, Analytic -- Periodicals; Optical materials -- Research -- Periodicals; Electronics -- Materials -- Research -- Periodicals; 543.0284
• DOI: 10.1039/c8tc00073e
• Languages: English
• ISSNs: 2050-7526

Abstract

Abstract : Thermoelectric properties (conductivity and Seebeck coefficient) are in screening for new tetrathiotetracene lead materials. Iodine doping reveals iPr, Me-TTT as optimal. Abstract : Reaction of elemental sulfur with 2-R 1 and 2, 8-R 1, R 2 -substituted tetracenes (2 ) in refluxing DMF affords 5, 6, 11, 12 tetrathiotetracenes (1 ) in good yields (74–99%) for a range of substituents where R 1, R 2 are: H, H (a ); Me, H (b ); MeO, H (c ); Ph, H (d ); Me, Me (e ), iPr, Me (f, iPr = iso-propyl, CHMe2 ), Me, MeO (g ); MeO, MeO (h ). The reaction rate is limited only by the solubility of the tetracene (2 );2g–h being both the least soluble and slowest reacting. At partial conversion recovered single crystalline2g led to its X-ray structure determination. Vacuum deposited (substrate deposition temperature 300 K, pressure 7 × 10 −6 mbar, source temperature 500 K) thin films from1 (of initial 88–99% purity) show final electrical conductivities, σ (in plane) from 1.40 × 10 −5 S cm −1 (1g ) to 3.74 × 10 −4 S cm −1 (1b ) for the resultant near pristine films; while1d proved too involatile to be effectively sublimed under these conditions. In comparison, initially 95% pure TTT (1a ) based films show σ (in-plane) = 4.33 × 10 −5 S cm −1 . The purities of1a–h are highly upgraded during sublimation. Well defined micro-crystallites showing blade, needle or mossy like habits are observed in the films. The Seebeck coefficients ( S b ) of the prepared1 range from 374 (1c ) to 900 (1f ) μV K −1 ( vs. 855 μV K −1 for identically prepared 95% pure TTT, 1a ). Doping of films of1f (R 1 = iPr, R 2 = Me) with iodine produces optimal p-type behaviour: σ (in-plane) = 7.00 × 10 −2 S cm −1, S b = 175 μV K −1 . The latter's power factor (PF) at 0.33 μW m −1 K −2 is more than 500 times that of the equivalent I2 -doped TTT films (1a, R 1 = R 2 = H), previously regarded as the optimal material for thin film thermoelectric devices using acene radical cation motifs.