Electron-Rich Dipyrrolonaphthyridinediones: Synthesis and Optical Properties

Abstract

This article describes the design rationale for highly electron-rich dipyrrolonaphthyridinedione (DPND) derivatives bearing substituted amino groups at the 3 and 9 positions, which exhibit absorption in the red and emission in the red/NIR region of the spectrum. These novel dyes are easily synthesized through a two-step protocol consisting of bromination of the DPND molecule followed by Buchwald-Hartwig amination. We demonstrated that the diamino-dipyrrolonaphthyridinediones have high ionization energies (∼4.7 eV) and that the spectroelectrochemical properties can be rationally tuned by altering the nature of the peripheral substituted amino groups. All amino-DPNDs exhibit solvatofluorochromism, which has not been previously reported for dyes possessing this core. Theoretical calculations reveal that in all cases, the strongest absorption is exhibited by the S states which clearly correlate with the HOMO-LUMO orbital transition. As all higher states have lower oscillator strengths, it is clear that fluorescence is completely dominated by the excitation/deexcitation sequence S → S, S → S and that there are no contributions to the fluorescence from excitations to higher states.

Singlet Fission in a Pyrrole-Fused Cross-Conjugated Skeleton with Adaptive Aromaticity

“…DPNDs are a series of cross-conjugated heterocyclic chromophores that show interesting electrochemical and photophysical properties. − Such a skeleton is composed of electron-rich pyrrole rings and electron-poor carbonyl moieties (Figure a) . From single-crystal data, we observed a slip-stack pattern of packing arrangement with a π–π distance of 3.38 Å between the closest planes of these two molecules, which make it favorable for possible SF and exciton diffusion process.…”

Potent strategy towards strongly emissive nitroaromatics through a weakly electron-deficient core

“…DPNDs are a series of cross-conjugated heterocyclic chromophores with unique photophysical and electrochemical properties that allow them to act as week electron donors or weak electron acceptors, 30,[35][36][37] making them an excellent choice for designing the D-A and A-D-A conjugates for this study. Biaryllike linkages enable weak coupling between the nitro group(s) and the DPND core (Fig.…”

Tuning the aromatic backbone twist in dipyrrolonaphthyridinediones

“…[9][10][11][12][13] The dipyrrolonaphthyridinedione (DPND) core 14 is a unique chromophore in that it is composed of cross-conjugated electronrich and electron-poor moieties (pyrrole rings and carbonyl groups, respectively). Recently, the DPND core has been successfully employed in the construction of dyes with red/NIR emission, 15,16 OFETs, 17 stable singlet fission (SF) materials 18 with a distinctive adaptive aromaticity (dual aromaticity) or fluorescent nitroaromatics. 19 Due to the presence of donor and acceptor moieties the DPND core is polarized.…”