Family of diazapentalene chromophores and narrow-band-gap polymers: Synthesis, halochromism, halofluorism, and visible-near infrared photodetectivity

A family of pyrrolo[3,4-c]pyrrol-1(2H)-one (PPO) and 2,5-diazapentalene (DAP) chromophores and DAP-containing polymers were synthesized, and their optical and electrochemical properties were studied. PPO and DAP chromophores are readily obtained by chemical transformation of the lactam unit in diketopyrrolopyrrole (DPP) dyes and can be used as versatile building blocks for construction of a variety of conjugated low-band-gap compounds and polymers. In comparison with the DPP chromophores, PPO and DAP chromophores have narrower energy gaps and low-lying HOMO levels in the order DPP > PPO > DAP. Interestingly, the PPO and DAP chromophores exhibit unique visible and near-infrared halochromic and halofluoric properties. The emission spectrum of DAP-containing polymer 6d covers the telecommunication window including the wavelength of 1310 nm. The photodetector with a device configuration of ITO/PEDOT:PSS (35 nm)/active layer (100 nm)/Al (100 nm) was fabricated using a blend of polymer 6d and [6,6]-phenyl-C ₆₁-butyric acid methyl ester (PC ₆₁BM) in a weight ratio of 1:3 as the active layer and exhibited photocurrent spectral response from 400 to 1000 nm and the detectivity in an order of 10 ¹¹ Jones at 800 nm.