Phenyl-Substituted Cibalackrot Derivatives: Synthesis, Structure, and Solution Photophysics

30 January 2023, Version 1
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

Three symmetrically and three unsymmetrically substituted cibalackrot (7,14-diphenyldiindolo[3,2,1-de:3',2',1'-ij][1,5]naphthyridine-6,13-dione, 1) dyes carrying two derivatized phenyl rings have been synthesized as candidates for molecular electronics and especially for singlet fission, a process of interest for solar energy conversion. Solution measurements provided singlet and triplet excitation energies and fluorescence yields and lifetimes; conformational properties were analyzed computationally. The molecular properties are close to ideal for singlet fission. However, crystal structures, obtained by single-crystal X-ray diffraction, are rather similar to those of the polymorphs of solid 1, in which formation of a charge-separated state followed by intersystem crossing, complemented with excimer formation, outcompetes singlet fission. Results of calculations by the approximate SIMPLE method suggest which ones among the solid derivatives are the best candidates for singlet fission, but it appears difficult to change the crystal packing in a desirable direction. We also describe the preparation of three specifically deuteriated versions of 1, expected to help sort out the mechanism of fast intersystem crossing in its charge-separated state.

Supplementary materials

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Supporting Information
Description
1H, 13C, 1H – 1H COSY, HSQC, HMBC NMR spectra for all new compounds, nanosecond transient absorption spectroscopy (TAS) measurements, and crystallography information.
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