Access to Triplet Excited State in Core-Twisted Perylenediimide

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• 作者：Kalaivanan Nagarajan ; Ajith R. Mallia ; V. Sivaranjana Reddy ; Mahesh Hariharan
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：April 28, 2016
• 年：2016
• 卷：120
• 期：16
• 页码：8443-8450
• 全文大小：504K
• 年卷期：0
• ISSN：1932-7455

文摘

Solvent-free crystal structure of N,N-bis(propylacetyl)-1,6,7,12-tetrabromoperylene-3,4:9,10-bis(dicarboximide), PDI-Br₄, obtained by X-ray diffraction reveals the core-twisted perylene motif having π–π stacks at an interplanar separation of 3.7 Å. Slip-stacked arrangement of PDI units in PDI-Br₄ arises due to the presence of bulky bromine atoms. Femtosecond pump–probe measurements of monomeric PDI-Br₄ in toluene reveal ultrafast intersystem crossing (τ_ISC < 110 fs) when excited at 400 nm. Triplet quantum yield (Φ_T) of 19 ± 1% and 105 ± 5% for PDI-Br₄ in toluene and vapor-annealed polycrystalline 60 nm thick film respectively are estimated from nanosecond transient absorption measurements. Quantum chemical calculations show that the combined effects of heavy atom and core-twist in PDI-Br₄ can activate the intersystem crossing by altering the singlet–triplet energy gap. Enhanced quantum yield accounts for the singlet fission mediated generation of triplet excited state in the PDI-Br₄ thin film.