Linear Extension of Anthracene via B←N Lewis Pair Formation: Effects on Optoelectronic Properties and Singlet O₂Sensitization

Abstract

The functionalization of polycyclic aromatic hydrocarbons (PAHs) via B ! NL ewis pair formation offers an opportunity to judiciously fine-tune the structural features and optoelectronic properties,tosuit the demands of applications in organic electronic devices,b ioimaging,a nd as sensitizers for singlet oxygen generation. We demonstrate that the N-directed electrophilic borylation of 2,6-di(pyrid-2-yl)anthracene offers access to linearly extended acene derivatives Py-BR (R = Et, Ph, C 6 F 5 ). In comparison to indeno-fused 9,10-diphenylanthracene,t he formal "BN for CC" replacement in Py-BR selectively lowers the LUMO,r esulting in am uchr educed HOMO-LUMO gap.A ne ven more extended conjugated system with seven six-membered rings in ar ow (Qu-BEt)i s obtained by borylation of 2,6-di(quinolin-8-yl)anthracene. Fluorinated Py-BPf shows particularly advantageous properties,i ncluding relatively lower-lying HOMO and LUMO levels,s trong yellow-green fluorescence,a nd effective singlet oxygen sensitization, while resisting self-sensitized conversion to its endoperoxide.

Bis-borylated arylisoquinoline-derived dyes with a central aromatic core: towards efficient fluorescent singlet-oxygen photosensitizers

“…The marked photoreactivity of linear acenes towards 1 O 2 is commonly ascribed to the formation of endoperoxides by means of a [4 + 2] cycloaddition. 32,36,67–70 Analogous chemical processes are expected for the naphthalene- and anthracene-derived 1 and 2 , respectively. Similar pyrene oxidation products by the action of 1 O 2 are not described.…”

“…1) have drawn attention as 1 O 2 photosensitizers. 32,36 Transient absorption spectroscopy was performed on the herein investigated dyes to detect excited triplet states. These could serve as precursors for the formation of 1 O 2 by means of energy transfer to triplet oxygen ( 3 O 2 ).…”

“…The Jäkle group has used BN Lewis-pair formation to extend the anthracene skeleton laterally (structure E ) 32 or linearly (structure F ). 36 This yielded red-shifted fluorescence, as compared to simple anthracene dyes, and photosensitized singlet-oxygen ( 1 O 2 ) formation. Using pyrene as the aromatic core led for example to structures G and H .…”

“…The Jäkle group has used BN Lewis-pair formation to extend the anthracene skeleton laterally (structure E) 32 or linearly (structure F). 36 This yielded redshifted fluorescence, as compared to simple anthracene dyes, and photosensitized singlet-oxygen ( 1 O 2 ) formation. Using pyrene as the aromatic core led for example to structures G and H. 31,33 Chromophores that exhibit efficient fluorescence, but also populate enough excited triplet state that could trigger the formation of 1 O 2 , are of interest because of their bimodal activity.…”

Synthesis, Photophysical, Electrochemical, and Non‐linear Optical Properties of Triaryl Pyrazole‐based B‐N Coordinated Boron Compounds

“…Pioneering studies to use B−N coordinated fluorophores as electron transporting materials by Yamaguchi and co‐workers inspired researchers to synthesize many B−N coordinated boron compounds and study their properties [16] . For instance Jäkle, Wang, groups reported the oxygen sensors [7a–c] and photochromic materials [14] whereas Ingleson group explored the acceptor‐donor systems [17] . More recently, Gilroy group reported photoluminescence and electrochemiluminescence of a boron based formazanate dye [18] …”