Systematic elongation of thienyl linkers and their effect on optical and electrochemical properties in carbazole-BODIPY donor-acceptor systems

Synthesis, spectral and electrochemical properties of a series of new panchromatic BODIPY donor-acceptor-donor derivatives, comprising carbazole conjugated with systematically elongated framework by thiophene-based linkers were investigated. It has been found that elongation of the π-system with one thiophene unit shifts the spectra toward near infrared, while incorporation of next thiophene derivatives has only limited influence on the lowest energy transition, causing no further shift of absorption maxima. Elongation of π-conjugation of the donor arm tunes the electron properties, influencing the ionization potential (IP) and electron affinity (EA) values of the molecules. The experimental results are supported by quantum chemical computations revealing that electron density of SOMO orbital is low at the 3-positions of terminal carbazole units in BODIPY push-pull oligomers while elongating their backbone, thus preventing them to undergo electrochemical polymerization giving reversibly p- and n-dopable products. Presented study tests the influence and limitations of incorporation of electron-rich substituents for designing panchromatic BODIPY systems.