Syntheses of Thiophene and Thiazole-Based Building Blocks and Their Utilization in the Syntheses of A-D-A Type Organic Semiconducting Materials with Dithienosilolo Central Unit

The effects of alkyl substitution on the aggregation of π-conjugated dyes: spectroscopic study and modelling

A family of dithienosilole-based dyes with alternating donor and acceptor conjugated groups, decorated with linear or branched alkyl chains at different positions on the backbone, have been obtained and investigated in different aggregation states. These dyes are characterized by almost panchromatic absorption and by near-IR emission, with good quantum yields in a variety of solvents with different polarity. We demonstrate that the nature and position of the alkyl substituents strongly govern the self-assembly of the dyes, whose packing is also sensitive to external stimuli, such as grinding and water addition. Thanks to computational results and theoretical modelling, we are able to interpret the results based on two possible preferential packings, characterized by distinct spectroscopic behaviour, whose abundance can be tuned according to the nature and position of the alkyl chains, as well as via external stimuli.

Theoretical investigations of the substituent effect on the opto-electronic properties of the linearly fused napthadithiophene-based molecules

The optoelectronic and charge transport properties of eight linearly fused Napthadithiophene (NDT) molecules with different electron-withdrawing (EWG) and electron-donating (EDG) substituents are studied using the density functional theory (DFT) methods. The effect of the substitution of EWG and EDG on the molecular structure, frontier molecular orbitals, ionization energy, electron affinity, reorganization energy, crystal packing, and charge carrier mobility are studied. The crystal structure simulation method is used to optimize the possible crystal packing arrangements for the studied molecules. The energy and distribution of electron density on the frontier molecular orbitals are strongly influenced by the substitution of EWG and EDG, thereby changes in the absorption spectrum and charge transport properties. The unsubstituted NDT molecule possesses a maximum hole mobility of 2.8 cm2 V-1 s-1, which is due to the strong intermolecular interactions. Therefore, the NDT molecule can be used as a p-type semiconducting material. Among the studied molecules, the CCH-substituted NDT molecule, NDT-CCH, possesses a higher electron mobility of 1.13 cm2 V-1 s-1. The C2H5-substituted NDT molecule, NDT-C2H5, possesses ambipolar behavior with mobility of 4.77 × 10-2 cm2 V-1 s-1 and 1.70 × 10-2 cm2 V-1 s-1 for hole and electron, respectively.