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Synthesis of Bis(arylethynyl)pyrrolo[3,2‐ b ]pyrroles and Effect of Intramolecular Charge Transfer on Their Photophysical Behavior
Author(s) -
Tasior Mariusz,
Clermont Guillaume,
BlanchardDesce Mireille,
Jacquemin Denis,
Gryko Daniel T.
Publication year - 2019
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201804325
Subject(s) - intramolecular force , chemistry , excited state , chromophore , solvatochromism , sonogashira coupling , photochemistry , two photon absorption , absorption (acoustics) , indole test , charge (physics) , dipole , crystallography , stereochemistry , atomic physics , molecule , physics , organic chemistry , optics , palladium , laser , quantum mechanics , catalysis
3,6‐Bis(arylethynyl)pyrrolo[3,2‐ b ]pyrroles were synthesized through a two‐step procedure involving double direct alkynylation of the electron‐rich core followed by Sonogashira coupling. In comparison with the parent tetraarylo‐pyrrolo[3,2‐ b ]pyrroles and benzo‐fused pyrrolopyrroles, these new dyes showed moderately redshifted absorption. Almost all derivatives showed positive fluorescence solvatochromism and, for the first time, red‐emitting pyrrolopyrroles were obtained. Computational studies revealed that, in most cases, there is negligible change in the geometry between ground and excited states. Interestingly, there was a fundamental difference between pyrrolopyrroles possessing electron‐withdrawing substituents at positions 2 and 5 and their analogs lacking these substituents. The former dyes behaved like dipolar chromophores with the lowest excited state both one‐photon and two‐photon allowed, which corresponds to intramolecular charge transfer occurring along the branches perpendicular to the pyrrolopyrrole long axis. In compounds lacking electron‐withdrawing substituents at positions 2 and 5, intramolecular charge transfer took place along the long axis of pyrrolopyrrole and consequently the one‐photon transitions are not two‐photon allowed. Despite displaying quadrupolar core‐to‐peripheral intramolecular charge transfer, these derivatives showed two‐photon absorption cross sections in the NIR1 region comparable to tetraaryl‐pyrrolo[3,2‐ b ]pyrroles lacking π‐expansion (up to about 500 GM).