Abstract
Copolymers alternating the BAI with thiophene-based moieties showed absorption and fluorescence in the NIR and were found to prevent ACQ.
Highlights
Three new copolymers based on bay-annulated indigo (BAI) building blocks were synthesized through Stille-type cross-coupling reactions, alternating the electron-deficient BAI units with thiophene-based donor moieties
For the synthesis of 7,14-di(thiophen-2-yl)diindolo[3,2,1-de:30,20, 10-ij][1,5]naphthyridine-6,13-dione (BAI1) indigo is first subjected to a double annulation reaction to form the BAI core
For the synthesis of the BAI-benzodithiophene copolymer PBAIBD-1, the reaction conditions were modified according to a report by He et al.[13]
Summary
Natural dyes and pigments as indigo (Scheme 1) and its natural (indigoids) or synthetic derivatives are valued for their bright color and high photochemical stability and have been used since antiquity.[1,2,3,4,5] A bay-annulated indigo derivative known as Cibalackrot (7,14-diphenyldiindolo[3,2,1-de;30,20,10-ij][1,5]naphthyridine-6,13-dione), an industrial dye that has been known for over a century,[6] has a highly rigid chemical structure, showing strong luminescence[7] and is, as indigo, capable of singlet fission[8,9] and can be used as an organic laser dye.[10]. Absorption spectra of the transparent thin films were obtained in absorption mode using a clean sapphire substrate as the reference sample. Fluorescence decays were measured using a home-built picosecond time-correlated single photon counting (ps-TCSPC) apparatus described elsewhere.[33] Excitation was performed with the second harmonic, 372 nm or 402 nm (generated with a Spectra Physics GWU-23PS module) from a picosecond Spectra Physics mode-lock Tsunami laser (Ti:Sapphire) model 3950 The time resolved ultrafast transient absorption measurements were collected in a broadband HELIOS spectrometer (350–1600 nm) from Ultrafast Systems as elsewhere described.[35] The transient absorption data was obtained with excitation at 420 nm and 770 nm and probed in the 350–800 nm and 800–1600 nm range. The reference and polymers were dissolved in 0.1 M NBu4PF6 in CHCl3 solution to acquire cyclic voltammograms with a 50 mV sÀ1 scan rate with a window potential between À1.6 V to 1.0 V (vs. Ag/Ag+)
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