A Conjugated Carboranyl Main Chain Polymer with Aggregation-Induced Emission in the Near-Infrared

Materials exhibiting aggregation-induced emission (AIE) are both highly emissive in the solid state and prompt a strongly red-shifted emission and should therefore pose as good candidates toward emerging near-infrared (NIR) applications of organic semiconductors (OSCs). Despite this, very few AIE materials have been reported with significant emissivity past 700 nm. In this work, we elucidate the potential of ortho-carborane as an AIE-active component in the design of NIR-emitting OSCs. By incorporating ortho-carborane in the backbone of a conjugated polymer, a remarkable solid-state photoluminescence quantum yield of 13.4% is achieved, with a photoluminescence maximum of 734 nm. In contrast, the corresponding para and meta isomers exhibited aggregation-caused quenching. The materials are demonstrated for electronic applications through the fabrication of nondoped polymer light-emitting diodes. Devices employing the ortho isomer achieved nearly pure NIR emission, with 86% of emission at wavelengths longer than 700 nm and an electroluminescence maximum at 761 nm, producing a significant light output of 1.37 W sr–1 m–2.

Atomic force microscopy (AFM) images of spin coated films (10 mg/mL solutions in chlorobenzene, 1000 rpm for 1 min) were obtained with an Agilent AFM 5500 setup in tapping mode, and processed with PicoView 1.5 software.Thermogravimetric analysis (TGA) was run on a Mettler Toledo TGA/DSC 1 from 25 to 750 °C with a heating rate of 5 °C/min under nitrogen.Differential scanning calorimetry (DSC) measurements were performed on a Mettler Toledo DSC 1 over three scans between 25 and 350 °C with a heating rate of 10 °C/min.Cyclic voltammetry (CV) was performed using an Autolab PGSTAT101 potentiostat with a glassy carbon working electrode, Pt counter electrode, and Ag/Ag + reference electrode in a 0.1 M solution of tetrabutylammonium hexafluorophosphate in acetonitrile, at a scan rate of 0.1 V/s.Samples were drop-cast onto the working electrode before conducting each measurement and ferrocene was added at the end of the measurements as an internal reference.Analytical gel permeation chromatography (GPC) was performed at 80 °C on an Agilent Technologies 1200 series chromatograph equipped with a refractive index detector, running in chlorobenzene with two PLgel mixed B columns in series.The system was calibrated against narrow polydispersity polystyrene standards.Computational models of each polymer, using trimers with methyl groups in place of alkyl chains for the sake of computational feasibility, were optimised with Gaussian 16 (revision C.01) at the B3LYP/6-311G** level. 1,2The same level of theory was used for rotational energy calculations.Molecular structures and orbitals were visualised in GaussView 5.0.Grazing-incidence wide-angle X-ray scattering (GIWAXS) measurements were performed at the BL11 NCD-SWEET at ALBA Synchrotron Radiation Facility (Barcelona, Spain).The incident X-ray beam energy was set to 12.4 eV using a channel cut Si (1 1 1) monochromator.The angle of incidence αi was set between 0.1° and 0.2° to ensure surface sensitivity.Data are expressed as a function of the scattering vector, which was calibrated using Cr2O3, obtaining a sample-to-detector distance of 145.6 mm.The scattering patterns were recorded using a Rayonix LX255-HS area detector, which consists of a pixel array of 1920 × 5760 pixels (H × V) with a pixel size of 44 × 44 µm 2 .All the measurements were performed under N2 atmosphere to minimize the damage of the films.2D GIWAXS patterns were corrected as a function of the components of the scattering vector (q).The steady-state photoluminescence (PL) emission spectra were measured with a Jobin Yvon Fluorolog spectrofluorometer from Horiba.The samples were excited using Xe lamp source and detected using PMT-Si detector with an extended correction range up to 1000 nm.The films were excited at 375 nm and appropriate combinations of bandpass and longpass filters were used to avoid 2 nd order diffraction.The emission spectra were corrected for the spectral sensitivity of the setup corresponding to the used configuration (detectors and gratings).4][5][6] All solutions were carefully optically matched by using a Cary 5000 UV-Vis-NIR spectrophotometer and measured under the same conditions.The refractive indexes of solvent mixtures were obtained from literature and respective polynomial fitting equation for the 99% mixture. 7For solid-state PLQY measurements, films were spin coated onto clean glass substrates (cleaning procedure outlined under device section below) from toluene solutions (5 mg/mL) at 2000 rpm for 60 seconds, followed by annealing at 100 °C for 10 min.][10] The monochromatic beam was incident at an angle of 60° to the film and emission was collected at the same angle.Solvatochromic absorption and PL spectra were measured on a Cary 60 UV-Vis Spectrophotometer, and a Cary Eclipse Fluorescence Spectrometer (λex = 375 nm), respectively.

Device fabrication OLEDs
Patterned indium tin oxide (ITO)-on-glass substrates (size 25.4 mm × 25.4 mm) were cleaned in a succession of ultrasonic baths using acetone, isopropanol, and detergent (Hellmanex III, 2 vol% DI water) for 15 min each, followed by UV ozone treatment in an MTI UV/Ozone ProCleaner.A 35 nm layer of PEDOT:PSS (AI 4083 from Heraeus) was deposited by spin coating at 3000 rpm and then annealed in nitrogen for 15 min at 135 °C followed by a 12 nm layer of TFB spin-coated from a 2 mg/mL toluene solution at 1000 rpm for 30 s.The TFB layer was annealed at 180 °C for 60 min in nitrogen.A 35 nm emissive layer was deposited via spin coating from a 5 mg/mL solution in toluene at 2000 rpm.Finally, the devices were transferred to an Angstrom glovebox evaporator where 30 nm of TPBi, 1 nm of LiF and 100 nm of Al were sequentially evaporated at a pressure of 1 × 10 -7 mbar.The devices were encapsulated and characterised in air using a Hamamatsu external quantum efficiency measurement system C9920-12 in conjunction with a Keithley 2400 sourcemeter and controlled using a PC.

SCLC
Hole-only devices were fabricated onto patterned ITO-coated glass.Prior to deposition, substrates were cleaned by sonication in detergent solution, water, acetone, and isopropyl alcohol for 15 min each.Devices were fabricated with the configuration ITO/PEDOT:PSS/CbT2-IDT/MoOx(10nm)/Ag.PEDOT:PSS was filtered and spin-coated onto the plasma-treated substrates to achieve ~50 nm thickness and annealed at 150°C for 15 min, followed by deposition of 110 nm active layers from chlorobenzene solutions at 2000 rpm under inert atmosphere.Layers of 10 nm MoOx and 100 nm Ag were subsequently deposited by evaporation through a shadow mask with pixel areas of 0.045 cm 2 .Active layer thicknesses were measured with a Dektak profilometer.  b] Measured from 1:9 THF:water.

Synthesis General
Chemicals were obtained from commercial sources and used without further purification, unless otherwise specified.Microwave reactions were run in a Biotage Initiator+ microwave reactor.Polymers were purified by preparative GPC on a Shimadzu UFLC prior to device fabrication.

Figure
Figure S1.a) TGA and b) DSC scans of polymers.
Figure S1.a) TGA and b) DSC scans of polymers.

Figure S4 .
Figure S4.DFT calculated energetic barrier of rotation around the carborane-thiophene bond of a single pCbT2-IDT repeat unit.

Figure S8 .
Figure S8.Absorption (solid lines) and PL (marked lines) spectra of polymer solutions (0.05 mg/mL or saturation) with various solvents.