A DFT/TDDFT modelling of bithiophene azo chromophores for optoelectronic applications

• Seven reported and five new bithiophene azo dyes are tested for their optoelectronic properties.
• DFT and TDDFT methods are used for modelling the properties.
• Azo group stabilizes LUMO whereas donor group contributes upto 70% towards HOMO.
• The push–pull character in these molecules is quantified using tools like GIAO, NBO and QTAIM.
• Four out of five new candidates show promise with lower band gap and higher wavelength absorption.

Sixteen Bithiophene azo derivatives (BTAs) containing thiazole moiety have been reported recently, and seven of them along with five new candidates have been tested for optoelectronic properties using DFT/TDDFT computations. FMO analysis clearly reveals that the substitution at bithiophene moiety largely stabilizes the HOMO while the LUMO is mainly localized on azo and thiazole moieties. Five new candidates with –NO2, –CN, –COOH, COCH3 and –COOCH3 as acceptors have been designed. Among the designed candidates, –NO2 substituted BTA (BTA8) is promising with an absorption maximum at 647 nm. Push–pull character has been quantified using NMR chemical shifts. Further, NBO analysis accounts for the n → π* and π → π* ground state stabilizing interactions arising from the heteroatoms in these BTAs. Four of the five designed candidates, are found to have reduced HOMO–LUMO energy gap, greater push–pull character along with higher wavelength of absorption and this render them very suitable for optoelectronic applications.

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