Synthesis, electrochemical, and optical properties of low band gap homo- and copolymers based on squaraine dyes

Abstract

A broad series of monomeric and polymeric squaraines was synthesized to investigate the impact of electrondonating bridges, such as unsaturated triarylamine, carbazole, and saturated piperazine groups, on the spectroscopic and redox properties. These bridges were attached to both standard trans-indolenine squaraines and dicyanomethylenesubstituted cis-indolenine squaraines. The conjugates were investigated by absorption, steady-state, and time-resolved fluorescence spectroscopy and cyclic voltammetry. While addition of the donors resulted in significant redshift of the absorption of the model compounds, hardly any further shift or broadening was observed for the copolymers. Also the redox proper-ties remained nearly unchanged compared with the model dyes. In contrast, immense broadening and redshift was observed for homopolymers. This behavior is explained by mostly excitonic coupling of localized squaraine transitions. The increasing distance of the chromophores determined by the bridges led to a decrease of the exciton coupling energy. We also performed semiempirical CNDO/S2 calculations on AM1 optimized structures. V C 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 890-911

Squaraine‐Based Polymers: Toward Optimized Structures for Optoelectronic Devices

“…Synthesis of pi‐conjugated polymers comprising squaraine building blocks is a promising approach to materials with small optical band‐gap featuring attractive properties for device applications . In particular, Ajayaghosh and Eldo reported the polycondensation of 1,4‐dialkoxydivinylbenzene‐bridged pyrrole derivatives (1‐methyl‐ and 1‐dodecylpyrrole) and squaric acid to access a series of squaraine‐based polymers with optical band gaps as low as 0.79 eV and excellent absorption range spanning the UV, visible, and near infrared region (300–1300 nm) .…”

“…(2 of 9) 1600487 Synthesis of pi-conjugated polymers comprising squaraine building blocks is a promising approach to materials with small optical band-gap featuring attractive properties for device applications. [28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44] In particular, Ajayaghosh and Eldo reported the polycondensation of 1,4-dialkoxydivinylbenzene-bridged pyrrole derivatives (1-methyl-and 1-dodecylpyrrole) and squaric acid to access a series of squaraine-based polymers with optical band gaps as low as 0.79 eV and excellent absorption range spanning the UV, visible, and near infrared region (300-1300 nm). [30,31] In addition, these polymers were found to exhibit fluorescence emissions with a relatively high quantum yields (Φ F up to 0.41), together with intrinsic electrical conductivities reaching 10 −4 S cm −1 without doping.…”

Exciton Transport in Molecular Aggregates – From Natural Antennas to Synthetic Chromophore Systems

“…Consequently, replacing thiophene by carbazole as a bridging unit reduced the exciton coupling even further. [232] Suzuki coupling methodology also allows the synthesis of copolymers with two different squaraine chromophores such as heteropolymers [SQA-SQB] n . The absorption spectra of this polymer show the typical shape of a J-aggregate both in CHCl 3 and in toluene which can also nicely be modelled by exciton coupling theory albeit with some more elaborate mathematics than in case of homopolymers.…”

Pyrrolyl Squaraines–Fifty Golden Years

“…Polysquaraines derived from bis-indolenine type molecules continue to provide a wealth of chemical possibilities as low band-gap materials [103] but the first two type I pyrrole-derived polysquaraines measured for electrical conduction were reported in 1997 by Ajayaghosh et al with (undoped) four point probe conductivities of 2.4 × 10 −6 and 2 × 10 −7 S/cm [10]. Since then the (undoped) electrical conductivities of pyrrole-derived squaraines have been reported thirteen times [15,17,[20][21][22]28,43,47,49,56,58,59,61], with the best conduction being no greater than 5 × 10 −4 S/cm [21].…”