4.1. Sample preparation

TDPP-Br (3,6-bis(5-bromo-2-thienyl)-2,5-bis(2-octyldodecyl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione, >98%) and DPPDTT (poly[2,5-(2-octyldodecyl)-3,6-diketopyrrolopyrrole-alt-5,5-(2,5-di(thien-2-yl)thieno [3,2-b]thiophene)], PDI: 2.03) were purchased from Osilla and used without any further purification (DPPDTT is also known as pDPPT-TT). TDPP-v-TDPP (E)-6,6′-(ethene-1,2-diylbis(thiophene-5,2-diyl))bis(2,5-bis(2-ethylhexyl)-3-(thiophen-2-yl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione) was synthesized by the Pd-catalysed Stille cross-coupling of bis(tributylstannyl)ethene with mono-brominated TDPP, following the methodology of Patil et al.⁶³ The reaction afforded a mix of the desired product and a major by-product, which were separated by a mixture of column chromatography over silica followed by preparative recycling gel permeation chromatography. TDPP-v-TDPP was characterized by ¹H NMR, ¹³C NMR and mass spectra (see Fig. S14–S19, ESI^†). The by-product was identified as the homo-coupled TDPP product (TDPP-TDPP) based on NMR and mass spectroscopy measurements, full details of the synthesis and purification procedures are given in Section S6 of the ESI.^†

All molecules were dissolved in either toluene or chloroform depending on their solubility. Solvents were purchased from Sigma Aldrich at HPLC grade (99.8% purity). For TA measurements, the solutions were diluted to have an absorbance between ∼0.3–0.4 at the peak wavelength of the pump laser in static 1 mm pathlength cuvettes. Fresh solutions were prepared before each measurement, and no sign of degradation was observed in visible absorption spectra acquired before and after ultrafast spectroscopic measurements. The fluorescence quantum yield of TDDP-Br was determined using a commercial fluorimeter and integrating sphere (Edinburgh Instruments, FS5).