Enhanced intersystem crossing in core-twisted aromatics. Issue 3 (18th January 2017)

• Record Type: Journal Article
• Authors: Nagarajan, Kalaivanan; Mallia, Ajith R.; Muraleedharan, Keerthi; Hariharan, Mahesh
• Is Part Of: Chemical science. Volume 8:Issue 3(2017)
• Page Start: 1776
• Page End: 1782
• Publication Date: 2017-01-18
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/c6sc05126j
• Languages: English
• ISSNs: 2041-6520

Abstract

Abstract : Core-twisted aromatics exhibit enhanced intersystem crossing upon photoexcitation when compared to their planar analogs. Abstract : We describe the design, bottom-up synthesis and X-ray single crystal structure of systematically twisted aromatics1c and2d for efficient intersystem crossing. Steric congestion at the cove region creates a nonplanar geometry that induces a significant yield of triplet excited states in the electron-poor core-twisted aromatics1c and2d . A systematic increase in the number of twisted regions in1c and2d results in a concomitant enhancement in the rate and yield of intersystem crossing, monitored using femtosecond and nanosecond transient absorption spectroscopy. Time-resolved absorption spectroscopic measurements display enhanced triplet quantum yields ( Φ T = 10 ± 1% for1c and Φ T = 30 ± 2% for2d ) in the twisted aromatics when compared to a negligible Φ T (<1%) in the planar analog3c . Twist-induced spin–orbit coupling via activated out-of-plane C–H/CC vibrations can facilitate the formation of triplet excited states in twisted aromatics1c and2d, in contrast to the negligible intersystem crossing in the planar analog3c . The ease of synthesis, high solubility, access to triplet excited states and strong electron affinity make such imide functionalized core-twisted aromatics desirable materials for organic electronics such as solar cells.