Enhanced intersystem crossing in core-twisted aromatics

Core-twisted aromatics exhibit enhanced intersystem crossing upon photoexcitation when compared to their planar analogs.

. Electrochemical properties of the derivatives 1c, 2d and 3c 14 6 Table S4. Photophysical properties of the derivatives 1c, 2d and 3c 14 7 Figure S1. 1  19 Figure S12. fTA spectra of 2d in toluene ( ex = 300 nm) obtained from the SVD analysis (SE-stimulated emission; TA-triplet absorption; GSB -ground state bleach. 20 20 Figure S13. a) Singlet and triplet energy levels of 1c, 2d and 3c calculated from TD-DFT at the basis set of BYLYP/6-311G++(d,p); b) comparison of low-lying singlet and triplet energy levels in the derivatives; c), d) and f) out of plane mode C-H bending in 1c, 2d and 3c respectively; g), h) and i) out of plane mode C=C bending in 1c, 2d and 3c respectively.

Materials and Methods:
All chemicals were obtained from commercial suppliers and used as received without further pu- Where, and denote the triplet quantum yield of the sample and reference respectively; and Where,  ISC -rate of intersystem crossing and  IC -rate of internal conversion; extracted from the fTA spectra analysis.

X-ray Crystallography:
High-quality specimens of appropriate dimensions were selected for the X-ray diffraction experiments. Crystallographic data collected are presented in the supplementary information.
Single crystals were mounted using oil (Infineum V8512) on a glass fibre. All measurements were made on a CCD area detector with graphite monochromated Mo Kα radiation. The data was collected using Bruker APEXII detector and processed using APEX2 from Bruker. All structures were solved by direct methods and expanded using Fourier techniques. The non-hydrogen atoms were refined anisotropically.
Hydrogen atoms were included in idealized positions, but not refined. Their positions were constrained relative to their parent atom using the appropriate HFIX command in SHELXL-97. The full validation of CIFs and structure factors of 1c and 2d were performed using the CheckCIF utility and found to be free of major alert level. 3D structure visualization and the exploration of the crystal packing of the derivatives were carried out using Mercury 3.1. Percentage (%) overlap was calculated from area of overlapped moieties of perylenediimide aromatic rings in the crystal structures. Percentage of overlapped aromatic area to total aromatic area gives the % overlap. 5 Computational Methods: Ground-state optimised structure and harmonic oscillator frequencies were computed using density functional theory (DFT) at the Beake's three parameter functional in combination with the Lee-Yang-Parr correlation functional (B3LYP) and 6-311+G(d,p) basis set.
Vertical excitation energies and oscillator strengths were calculated employing time dependent DFT (TD-DFT) at the B3LYP/6-311+G(d,p) level of theory. All computations were performed with the Gaussian 09 program suite. 6

Synthesis and Characterisation:
Synthesis of 1a and 2a 7.5 g of PTCDA (1) was stirred with 80 mL of concentrated sulphuric acid for 4 hours. 500 mg of elemental iodine was added and the reaction mixture was heated to 85°C. 1or 2 equivalents of elemental bromine was added drop wise to synthesise 1-bromo (1') and 1,7-dibromo (2') PTCDA respectively.
The reaction mixture was refluxed for 24 hours. After 24 hours, the product was precipitated by pouring the reaction mixture into 200 mL of ice water. The product (PTCDA-Br 1-2 ) was filtered and dried in hot air oven. Since, the product was insoluble in any solvent, subjected to imidisation reaction without further purification.           Energy, eV Figure S13. a) Singlet and triplet energy levels of 1c, 2d and 3c calculated from TD-DFT at the basis set of BYLYP/6-311G++(d,p); b) comparison of low-lying singlet and triplet energy levels in the derivatives; c), d) and f) out of plane mode C-H bending in 1c, 2d and 3c respectively; g), h) and i) out of plane mode C=C bending in 1c, 2d and 3c respectively.