jp0c01786_si_001.pdf (1.24 MB)
Singlet and Triplet Excited-State Dynamics of 3,7-Bis(arylethynyl)phenothiazines: Intramolecular Charge Transfer and Reverse Intersystem Crossing
journal contribution
posted on 2020-08-07, 13:09 authored by Madhurima Poddar, Alessio Cesaretti, Elena Ferraguzzi, Benedetta Carlotti, Rajneesh MisraA series
of 3,7-bis(arylethynyl)-substituted phenothiazine-based fluorophores
(bearing benzene, naphthalene, methoxynaphthalene, anthracene, phenanthrene,
and pyrene) were designed and synthesized via a Pd-catalyzed Sonogashira
cross-coupling reaction. These molecules show in solution large Stokes
shifts (generally 5500–6500 cm–1) and high
quantum yields (40–82% depending on the aryl groups), as a
consequence of the planarization of their butterfly-like structure
occurring in the excited state. Moreover, significant two-photon absorption
was revealed for these phenothiazine derivatives, whose cross section
increases upon enhancing the molecular conjugation. The remarkable
Stokes shifts, fluorescence quantum yields, and two-photon absorption
make these molecules appealing as fluorescent probes for bioimaging
applications. Significant emission was also detected in the solid
state where anthracene-, phenanthrene-, and pyrene-substituted phenothiazines
show red-shifted emission maxima compared to the solution, indicating
considerable π–π staking. The anthracene-substituted
phenothiazine arouses particular interest, as it exhibits photoinduced
intramolecular charge transfer (ICT) from the phenothiazine to the
anthracene, revealed by its important fluorosolvatochromism and through
ultrafast transient absorption experiments. The spectroscopic results
are in line with the time-dependent density functional theory (TD-DFT)
calculations and cyclic voltammetry measurements. The anthracene-substituted
molecule also features a remarkable triplet production and hints of
a delayed fluorescence behavior, allowed in nonpolar solvents by a
fairly competitive reverse intersystem crossing pathway. These findings
make the investigated molecules interesting as new organic active
materials for optoelectronic devices.
History
Usage metrics
Categories
Keywords
Stokes shiftssolutionexhibits photoinduced intramolecula...pyrene-substituted phenothiazines s...phenanthreneanthracene-substitutedanthracenecyclic voltammetry measurementsfluorescence quantum yieldsmoleculetwo-photon absorptionPd-catalyzed Sonogashira cross-coup...ICTTD-DFTTriplet Excited-State Dynamics
Licence
Exports
RefWorks
BibTeX
Ref. manager
Endnote
DataCite
NLM
DC