Boron Dipyrrin Dyes Exhibiting “Push–Pull–Pull” Electronic Signatures

Abstract

Manipulating the electronic pathway: A strategy has been devised for functionalizing boron dipyrrin dyes with one or two electroactive ferrocene units at the periphery. Oxidation of one or both ferrocene residues is fully reversible and gives rise to near‐IR electrochromism. One‐electron oxidation of the bis‐derivative transforms the original “push–pull–push” system into a “push–pull–pull” signature.

Synthesis of boron-dipyrromethene–ferrocene conjugates

“…However, the most remarkable feature of the absorption spectra of BODIPY-ferrocene conjugates 1-4 with an exception of compound 4 is the presence of an additional very broad band in 600-680 nm region. This low energy band observed in compounds 1-3 was assigned to the intramolecular charge transfer band [5,6] which is very intense for compound 2 in which two ferrocenyl moieties are present as compared to 1 and 3 which contain one ferrocenyl moiety. This is also reflected in the intense blue colour solution of compound 2 compared to violet and brown colour solutions of compounds 1 and 3, respectively (Fig.…”

“…The oxidation of Fe II to Fe III ion can be achieved by electrochemically as well as chemically. Yin et al [5] and Ziessel et al [6] in their independent work on vinylferrocene-BODIPY conjugates showed on/off optical switching of BODIPY unit by modulating the oxidation state of ferrocene electrochemically. Our lab is not equipped to perform spectroelectrochemical studies on these BODIPY-ferrocene conjugates hence we followed the changes occured in absorption and fluorescence spectra of BODIPY unit in conjugates 1 and 2 by oxidizing ferrocene to ferrocenium ion using oxidizing agent.…”

“…The solvent was removed on rotary evaporator under vacuo and afforded pure 5 as purple powder (457 mg, 60% yield). 1 -4-bora-3a,4a-diaza-sindacene (6) This compound 6 was prepared by following the same procedure mentioned for 5 using two equivalents of N-bromosuccinimide instead of one equivalent used for the preparation of 5. The TLC analysis showed two spots corresponding to 3-bromo derivative of boron-dipyrromethene 5 as minor spot and the desired 3,5-dibromo derivative of BODIPY 6 as major spot.…”

“…Although there are several reports on ferrocene connected chromophores such as porphyrins [4], until recently there are no reports on boron-dipyrromethene ferrocene conjugates. Recently, while our work was in progress, two independent groups [5,6] simultaneously published BODIPY dyes possessing one and two redox-active vinyl ferrocene groups at 3-and 3-, 5-positions, respectively. They demonstrated reversible electrochromism in these conjugates.…”

Substituted Diketopyrrolopyrroles as Input Energy Units in Soluble Donor–Acceptor Dyads

“…This latter situation is due to the presence of the bulky methyl groups in the 1,7-substitution position. [14] Close examination of the spectroscopic properties reveals interesting features. Absorption spectra recorded for compounds 2, 3 a, and 3 b in dioxane displayed features typical of the soluble DPP dyes, namely, a strong absorption in the visible region at around 480 nm.…”