Multiwavelength Photodetectors Based on an Azobenzene Polymeric Ionic Liquid

Abstract

Organic photodetectors (OPDs) are a promising class of light-detecting devices that can be created with simple fabrication techniques from a large variety of chemical building blocks. While molecular photoswitches are commonly used to modulate the properties of these devices through reversible isomerization or charge transfer, this responsive behavior is typically limited to a small range of wavelengths. Here, we report the characteristics of multiwavelength photodetectors using bilayers of a light-responsive azobenzene polymeric ionic liquid (PIL) in conjunction with the semiconducting polymer poly{( 4). Both ultraviolet (UV) and visible light induce a 10 2 −10 3 increase in current at a constant voltage within 10 s, which decays immediately when the light is turned off. This light-mediated performance is fatigue-resistant across multiple ON/OFF cycles and can be modulated with wavelengths far into the visible region (660 and 700 nm). Frontier energy level calculations of the light-induced charge carrier density indicate that this light-responsive increase in current is due to photoexcitation and a subsequent charge-transfer process between the azobenzene polymeric ionic liquid and the semiconducting polymer. In summary, the device described in this report exhibits sensing capabilities for multiple wavelengths of light corresponding with the azobenzene absorption profile.

Reversible Modulation of Conductivity in Azobenzene Polyelectrolytes Using Light

“…When exposed to UV irradiation (365 nm, 5 mW/cm 2 for 60 s), the π → π* transition bleaches and a stronger n → π* absorption is observed corresponding to 53% isomerization of trans -to- cis -azobenzene (see Figure S22). , Signatures of vibronic absorbance are partially retained for UV-irradiated films, as a fraction of the trans -azobenzene remains. ,,, …”

“…29,30 Signatures of vibronic absorbance are partially retained for UV-irradiated films, as a fraction of the trans-azobenzene remains. 9,15,31,32 The glass-transition temperatures (T g ) of the cis and trans poly(azobenzene) and poly(azo-co-IL) adducts were measured using DSC to understand how illumination changes segmental motion. The T g values of cis (4.6 °C) and trans (12.6 °C) poly(azobenzene) (see Figure S17) exhibit a similar trend as those of cis (7.4 °C) and trans (18.9 °C) poly(azo-co-IL).…”

“…Previously, we demonstrated the synthesis of polyelectrolytes containing azobenzene for use in photodetector applications, which relied on the dye-sensitizing ability of azobenzene to stimulate charge transfer with a semiconducting polymer. Here, we leverage trans – cis isomerization to control ionic conductivity.…”

A review: advancing organic electronics through the lens of ionic liquids and polymerized ionic liquids

“…48). 227 This photodetector, which is based on an azobenzene polymeric ionic liquid, can detect light at several wavelengths that correspond to the azobenzene's absorption spectrum. Bates and coworkers forged this light-detecting device by blending a light-responsive azobenzene-based polymeric ionic liquid as a gate layer with a semiconducting p-type polymer poly[(4,4-dihexadecyl-4 H -cyclopenta[1,2- b :5,4- b ′]dithiophene-2,6-diyl)- alt -(2,3-difluoro-1,4-phenylene)](PhF-2,3).…”

A functionalized CNT-azobenzene-PVA-based self-healing aqueous gel as a conductive photo-responsive actuator

“…Recently, switchable conductance with light via photochromic moieties, such as azobenzene, diarylethene, and spiropyran has acquired a lot of attention because of its applications in contact-free manipulation of conductance as optical switches. [63][64][65][66][67][68] Sciascia et al, used diarylethene as an optical switch for SWCNT-incorporated polymer composite. 69 Heinke and coworkers presented a MOF with spiropyran as a photochromic molecule for electronic conductance switching.…”