New A-D-A-D-A unsophisticated small molecules based on benzothiadiazole and thiophenewere designed and synthesized in a two-step pathway, involving the coupling benzothiadiazole with thiophene-, or bithiophene-carboxaldehyde, followed by Knoevenagel condensation. The first step was specifically investigated in comparing different coupling methods and their related green metrics. It is established that the synthesis of benzothiadiazole-based small molecules via direct heteroarylation may be an environmentally attractive procedure. It generates low polluting wastes in a cost-effective way in comparison to classical Suzuki coupling. Moreover, the direct arylation using low loading of palladium-catalyst whithout ligand nor additive is the method of choice for the present case. The physico-chemical properties of the four target molecules were investigated using electronic absorption spectroscopy, differential scanning calorimetry, cyclic voltammetry, polarized optical miscroscopy and small angle X-ray analysis. DFT studies have been performed to support the electronic characteristics.15 these numbers are maximum values deduced from (non-negociated) prices of commercial raw materials, always more expensive at laboratory scale than for upscaling or industrial purpose.The good figures of merit obtained for total E-factors as well as for the costs are undoubtedly linked to the fact that the target molecules are obtained in only two steps, which do not require column chromatography technics for their purification. The simple purification technics used in this work, i.e. washing or recristallization, are useful tools for green methods. Electronic properties.The UV-vis absorbance and fluorescence in CH 2 Cl 2 solution were recorded at room temperature (see Fig. 1 and Table 5). It is noticeable that the nature of the alkyl chain (R = octyl or 2-ethylhexyl) does not influence the absorption spectrum. The large absorption band that peaks at 497 nm and 522 nm for Bz(T 1 CAR) 2 and Bz(T 2 CAR) 2 , respectively, can be attributed to the intramolecular charge transfer (ICT) transition. 46,47 It should be noted that the increase of the number of thiophene units from one to two at both sides of the benzozothiadiazole induces a red shift of 25 nm, as a result of the extent of the conjugation. The observed Stokes shifts for compounds Bz(T 1 CAR) 2 and Bz(T 2 CAR) 2 are of 2500 to 3000 cm -1 . 20 treatment, meanwhile the recrystallization occurs at 144°C (∆H = 12 kJ mol -1 ). For Bz(T 2 CAO) 2 , the sharp fusion peak recorded at 193°C during the first cycle (not shown here) is splitted into two transitions at 173°C (∆H = 30 kJ mol -1 ) and 186°C (∆H = 10 kJ mol -1 ), indicating the possible presence of conformational polymorphs due to thermal treatment. The recrystallization is characterized by a peak at 157 °C (∆H = 25 kJ mol -1 ) immediately followed by a broad and weak transition at around 142°C. Bz(T 1 CAEH) 2 shows a large endothermic peak at around 175°C (∆H = 32 kJ mol -1 ), which corresponds to the phase transition from the crys...

5‐(7‐Bromo‐2,1,3‐benzothiadiazol‐4‐yl)‐2‐thiophenecarbaldehyde is a small building block of great interest for its use in the elaboration of symmetrical or unsymmetrical donor–acceptor π‐conjugated molecules for optoelectronic applications. Herein, a convenient, one‐pot, two‐component synthesis of this intermediate is reported, based upon a palladium‐catalysed, phosphine‐ and additive‐free, direct C–H arylation process. The synthesis has been studied in depth to obtain optimum yields and selectivity by an efficient and environmentally friendly strategy for sustainable synthesis.