Intramolecular Excimer Formation between 3,6-Di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione Chromophoric Groups Linked by a Flexible Alkyl Spacer

Abstract

Bichromophoric molecules containing two 3,6-di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (DPP) moieties linked via aliphatic spacers of different length are synthesized. Optical absorption spectroscopy indicates that the molecules adopt an extended conformation in solution. Fluorescence spectroscopy shows that photons are emitted from the locally excited singlet state in an extended conformation. In sufficiently polar solvents, quenching of fluorescence occurs and fluorescence quantum yield (ΦF) and fluorescence lifetime (τF) measurements indicate formation of an intramolecular excimer as the quenching mechanism. The redox potentials of the molecules and the solvent polarity dependence of the quenching are consistent with significant charge-transfer character of the excimer state. Photoinduced absorption measurements show enhanced intersystem crossing to the triplet state in polar solvents. Results indicate that in donor-acceptor π-conjugated materials involving the DPP moiety, excimer-like interchain polaron pair excited states could play an important role in the photophysics because of their close proximity in energy to the lowest singlet excited state.

Tuning the Optical Characteristics of Diketopyrrolopyrrole Molecules in the Solid State by Alkyl Side Chains

“… 27 , 28 , 32 , 38 − 43 For DPP-based molecules specifically, it is known that charge-transfer states between DPP units play a role in singlet fission and that favorable relative orientations between minimally two chromophores are required for triplet formation. 32 , 44 …”

Effect of Varying Thiophene Units on Charge‐Transport and Photovoltaic Properties of Poly(phenylene ethynylene)‐alt‐poly(phenylene vinylene) Polymers

“…In the less polar solvent, chloro­form, higher values were found for both parameters. Polymer EDOTE‐PV ab showed by far the lowest quantum efficiency of the three polymers, which might be due to higher interchain interactions favoring excimer formation and non‐radiative decay that decreases the emission efficiency . Generally, these polymers show rather low fluorescence quantum efficiency, which was further confirmed by kinetic experiments.…”

“…The highest rate constant of radiationless deactivation (Table ) might also be correlated with this nature where there is intrachain and interchain interaction in the entire structure for radiationless relaxation. In case of TE‐PV ab , and BTE‐PV ab the films are relatively rough with grains, which indicates better separation of the backbones by alkoxy side chains …”

“…The charge‐carrier transport in polymer EDOTE‐PV ab is lower than in the other two polymers TE‐PV ab and BTE‐PV ab . This might be linked to its high PDI value probably leading to morphological irregularities, which may impede the transport …”

Interplay between Electronic Energy Transfer and Reversible Photoreactions in a Triad Comprising Two Different Styrylbenzoquinoline Photochromes and a ′Hidden′ Quencher

“…Multi-chromophoric molecular systems, including covalently linked dyads and triads, attract much attention as models for experimental and theoretical studies of inter-chromophore interactions leading to excimer formation, [1][2][3][4][5][6] energy and/or electron transfer. [7][8][9][10][11][12][13][14][15][16][17][18] In the case when chromophores are also photochromes capable of reversibly photoisomerizing between two stable forms (isomers), multi-photochromic systems can serve as molecular digital switches and logic gates.…”