Synthesis of a near-infrared light-absorbing polymer based on thiophene-substituted Aza-BODIPY

Abstract

An alternating conjugated polymer with thiophene-substituted aza-boron dipyrromethene (BODIPY) was synthesized in which the carbon atom at the meso-position in the ligand moiety was replaced by nitrogen. Initially, it was found that the synthesized polymer had a significant near-infrared (NIR) light-absorbing ability. In the absorption spectrum, a large absorption band (molar extinct coefficient emax = 48,000 M−1 cm−1) with a peak at 864 nm was detected in the deep NIR region, even above 1300 nm. From cyclic voltammetry (CV) data, the energy levels of the frontier orbitals were determined. Accordingly, the polymer had a deep lowest unoccupied molecular orbital (LUMO) level (−4.01 eV), and this value was similar to that of the monomer. This result indicates that extension of π-conjugation throughout the polymer main-chain influenced only the highest occupied molecular orbital (HOMO) level while preserving the LUMO. The alternating conjugated polymer was synthesized with thiophene-substituted aza-boron dipyrromethene. The synthesized polymer had the near-infrared light-absorbing ability (molar extinct coefficient: 48,000 M−1cm−1) in the region over 1300 nm with the peak at 864 nm. From the electrochemical data, it was found that the polymer had the deep lowest unoccupied molecular orbital (LUMO) level. This result means that only the highest occupied molecular orbital level was influenced and the LUMO can be preserved by extension of π-conjugation through the polymer main-chain.