Photoluminescence of Squaraine Thin Films: Spatial Homogeneity and Temperature Dependence

Freese, Stefanie; Lassing, P.; Jakob, René; Schulz, Matthias; Lützen, Arne; Schiek, Manuela; Nilius, Niklas

doi:10.1002/pssb.201800450

Cited by 5 publications

(9 citation statements)

References 33 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Squaraines, which have useful optical properties, such as a sharp and intense absorption in the red-to-NIR wavelength region as well as high fluorescence quantum yields, − and form supramolecular aggregates − and polymeric foldamers, , would also be a suitable system for studying chirality as in the aforementioned cases. Yet, the literature on chiral squaraines is rather limited.…”

Section: Introductionmentioning

confidence: 99%

Chiroptical Properties of Indolenine Squaraines with a Stereogenic Center at Close Proximity

et al. 2020

View full text Add to dashboard Cite

A series of four indolenine squaraines bearing a chiral center at the 3-position of the indolenine moiety, with either an n-propyl or a phenyl group alongside a methyl group, were synthesized and obtained in a high purity of ≥98% for the desired stereoisomer. The indolenine precursors with a phenyl group attached at the chiral center were asymmetrically synthesized using a pericyclic-reaction cascade and obtained in a high ee of 98%, whereas the ones with an n-propyl group were prepared by kinetic resolution through asymmetric hydrogenation, resulting in an ee of up to 98%. X-ray crystallography revealed a slightly twisted geometry for the phenyl-substituted cisoid squaraine derivative, whereas the n-propyl-substituted derivative possessed the expected planar geometry. Variation of the substitution also influenced the optical properties, where the introduction of phenyl groups caused a progressive red-shift and reduction in squared transition moments, as well as reduced fluorescence quantum yields, Stokes shifts, and fluorescence lifetimes. All of the investigated compounds exhibited strong ECD signals, with Δε values of up to 24 M −1 cm −1 for the HOMO−LUMO transition. DFT calculations indicated that this was due to both large electric and magnetic transition moments, although the two vectors were mutually almost orthogonal.

show abstract

Section: Introductionmentioning

confidence: 99%

Chiroptical Properties of Indolenine Squaraines with a Stereogenic Center at Close Proximity

et al. 2020

View full text Add to dashboard Cite

show abstract

“…Squaraine assemblies in the form of covalently bound dimer and trimer complexes, − polymers, , and crystals − have attracted considerable attention as fundamental frameworks for studying aggregate photophysics and exciton transport . In squaraine polymers, for example, the exciton diffusion rate (10–100 ps –1 ) was found to be significantly larger than in conjugated polymers such as MEH-PPV .…”

Section: Introductionmentioning

confidence: 99%

“…In the Kasha model, both components are split symmetrically about the peak monomer absorption frequency, with the splittingthe DSequal to twice the transition dipole–dipole coupling. DS has been observed in the absorption spectra of squaraine dimers and higher order assemblies including thin films for OPV. ,− ,, The aim of the present work is to analyze the absorption spectral line shape in squaraine dimers using the ESM of Painelli and co-workers − as a first step in a broader investigation to fundamentally understand the nature of energy transport in D–A–D complexes.…”

Section: Introductionmentioning

confidence: 99%

“…DS has been observed in the absorption spectra of squaraine dimers and higher order assemblies including thin films for OPV. 1,[7][8][9]23,24 The aim of the present work is to analyze the absorption spectral line shape in squaraine dimers using the ESM of Painelli and coworkers 11−15 as a first step in a broader investigation to fundamentally understand the nature of energy transport in D−A−D complexes.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Davydov Splitting in Squaraine Dimers

et al. 2019

View full text Add to dashboard Cite

The essential states model (ESM) for donor− acceptor−donor (D−A−D) chromophores is used to explore absorption and photoluminescence (PL) in molecular dimers composed of centrosymmetric and non-centrosymmetric squaraine molecules. The spectral line shapes and shifts relative to the monomer spectrum are due to an interesting interplay between three-center charge distributions responsible for ground-and excited-state (permanent) dipole and quadrupole moments and two-center charge distributions responsible for transition dipole moments. The Davydov splitting is sensitive only to the interactions between the (extended) transition dipoles , whereas the permanent dipole-dipole and quadruple-quadrupole interactions impact the midpoint frequency of the two Davydov components, leading to a generally asymmetric splitting relative to the peak monomer transition frequency. The theory accurately reproduces the steady-state absorption and PL line shapes recently obtained for covalently bound squaraine dimers. The ESM also predicts an extreme type of non-Kasha behavior, where both Davydov components are blue-shifted above the monomer transition frequency.

show abstract

“…Here, the polymorph formation is controlled by thermal postannealing of the samples as discussed earlier. 27,34 In other work, also the solvent and amorphous coatings on the substrates have been found to be influential on the polymorph formation in addition to annealing temperature but without changing the out-of-plane orientation. 28 Those results have been obtained for spincasting of blended solutions containing a soluble fullerene acceptor such as PCBM, which has not altered crystallization propensity and crystallographic orientation.…”

Section: Introductionmentioning

confidence: 86%

Template and Temperature Controlled Polymorph Formation in Squaraine Thin Films

Balzer,

Breuer,

Witte

et al. 2022

Preprint

Self Cite

View full text Add to dashboard Cite

Controlling the polymorph formation in organic semiconductor thin films by the choice of substrate and deposition temperature is a key factor for targeted device performance. Small molecular semiconductors such as the quadrupolar donor-acceptor-donor (D-A-D) type squaraine compounds allow both solution and vapor phase deposition methods. A prototypical anilino squaraine with branched butyl chains as terminal functionalization (SQIB) has been considered for photovoltaic applications due to its broad absorption within the visible to deep-red spectral range. Its optoelectronic properties depend on the formation of the two known polymorphs adopting a monoclinic and orthorhombic crystal phase. Both phases emerge with a strongly preferred out-of-plane and rather random in-plane orientation in spincasted thin films depending on subsequent thermal annealing. Upon vapor deposition on dielectric and conductive substrates, such as silicon dioxide, potassium chloride, graphene and gold, the polymorph expression depends on the choice of growth substrate. In all cases the same pronounced out-of-plane orientation is adopted, but with a surface templated in-plane alignment in case of crystalline substrates. Combining X-ray diffraction, atomic force microscopy, ellipsometry and polarized spectro-microscopy we identify the processing dependent evolution of the crystal phases, correlating morphology and molecular orientations within the textured SQIB films.

show abstract

Photoluminescence of Squaraine Thin Films: Spatial Homogeneity and Temperature Dependence

Cited by 5 publications

References 33 publications

Chiroptical Properties of Indolenine Squaraines with a Stereogenic Center at Close Proximity

Chiroptical Properties of Indolenine Squaraines with a Stereogenic Center at Close Proximity

Davydov Splitting in Squaraine Dimers

Template and Temperature Controlled Polymorph Formation in Squaraine Thin Films

Contact Info

Product

Resources

About