Exciplex formation in solid state blends of charge-transfer type AFX dyes and bisimide compounds

Dalton, Matthew J.; Kannan, Ramamurthi; Swiger, Rachel N.; Orseno, Dominic L.; Haley, Joy E.; Cooper, Thomas M.; Tan, Loon‐Seng

doi:10.1117/12.931674

Cited by 3 publications

(3 citation statements)

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“…Because the effective σ 2 is also sensitive to the polarity of the local environment, , our report examines the solvent-dependent structure–property photophysical relationships of three of these molecules: 7-(benzo[ d ]thiazol-2-yl)-9,9-diethyl- N , N -diphenyl-9 H -fluoren-2-amine (AF240, D−π–A type), 9,9-diethyl- N2 , N2 , N7 , N7 -tetraphenyl-9H-fluorene-2,7-diamine (DPA2F, D−π–D type), and 2,2′-(9,9-diethyl-9 H -fluorene-2,7-diyl)dibenzo[ d ]thiazole (BT2F, A−π–A type) (Figure ). These dyes have been studied previously in our group in spin-cast films blended with bisphthalimides for exciplex formation. , Solvent-dependent studies by Belfield et al on similar dyes and BT2F revealed strong solvatochromism on the emission spectra of D−π–A derivatives, but little dependence in symmetrical molecules. They also showed that a solvent-stabilized state is formed in the asymmetrical fluorene but showed no direct evidence of this process.…”

Section: Introductionmentioning

confidence: 90%

“…These dyes have been studied previously in our group in spin- cast films blended with bisphthalimides for exciplex formation. 29,30 Solvent-dependent studies by Belfield et al on similar dyes 31 and BT2F 32 revealed strong solvatochromism on the emission spectra of D−π−A derivatives, but little dependence in symmetrical molecules. They also showed that a solventstabilized state is formed in the asymmetrical fluorene but showed no direct evidence of this process.…”

Section: ■ Introductionmentioning

confidence: 98%

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Symmetry- and Solvent-Dependent Photophysics of Fluorenes Containing Donor and Acceptor Groups

et al. 2014

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Three two-photon absorption (2PA) dyes (donor-π-donor (DPA2F), donor-π-acceptor (AF240), and acceptor-π-acceptor (BT2F); specifically, D is Ph2N-, A is 2-benzothiazoyl, and the π-linker is 9,9-diethylfluorene) are examined in a variety of aprotic solvents. Because the 2PA cross section is sensitive to the polarity of the local environment, this report examines the solvent-dependent linear photophysics of the dyes, which are important to understand before probing more complex solid-state systems. The symmetrical dyes show little solvent dependence; however, AF240 has significant solvatochromism observed in the fluorescence spectra and lifetimes and also the transient absorption spectra. A 114 nm bathochromic shift is observed in the fluorescence maximum when going from n-hexane to acetonitrile, whereas the lifetimes increase from 1.25 to 3.12 ns. The excited-state dipole moment for AF240 is found to be 20.1 D using the Lippert equation, with smaller values observed for the symmetrical dyes. Additionally, the femtosecond transient absorption (TA) spectra at time zero show little solvent dependence for DPA2F or BT2F, but AF240 shows a 52 nm hypsochromic shift from n-hexane to acetonitrile. Coupled with the solvatochromism in the fluorescence and large excited-state dipole moment, this is attributed to formation of an intramolecular charge-transfer (ICT) state in polar solvents. By 10 ps in AF240, the maximum TA in acetonitrile has shifted 30 nm, providing direct evidence of a solvent-stabilized ICT state, whose formation occurs in 0.85-2.71 ps, depending on solvent. However, AF240 in nonpolar solvents and the symmetrical dyes in all solvents show essentially no shifts due to a predominantly locally excited (LE) state. Preliminary temperature-dependent fluorescence using frozen glass media supports significant solvent reorganization around the AF240 excited state in polar solvents, and may also support a twisted intramolecular charge-transfer (TICT)-state contribution to the stabilization. Finally, time-dependent density functional theory calculations support ICT in AF240 in polar media and also allow prediction of the 2PA cross sections in the 0-0 band, which are much larger for AF240 than the symmetrical dyes.

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Section: Introductionmentioning

confidence: 90%

Section: ■ Introductionmentioning

confidence: 98%

Symmetry- and Solvent-Dependent Photophysics of Fluorenes Containing Donor and Acceptor Groups

et al. 2014

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“…These bisimides have flexible metaphenoxy or hexafluoropropyl linkers that are particularly suited to decrease the crystallinity of the phthalimide moiety to facilitate the preparation of amorphous blends for NLA applications in which optical clarity is important. They are particularly novel in that they have enough electron affinity to induce charge separation or exciplex formation in solid-state blends with NLA dyes 42 without the strong phase separation often seen due to the aggregation of perylenediimides or other stronger acceptors.…”

Section: ■ Introductionmentioning

confidence: 99%

Exciplex Formation in Blended Spin-Cast Films of Fluorene-Linked Dyes and Bisphthalimide Quenchers

et al. 2013

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Spin-cast films of dyes (donor-π-donor, donor-π-acceptor, and acceptor-π-acceptor type, where the donor is Ph2N-, the acceptor is 2-benzothiazoyl, and the π-linker is 9,9-diethylfluorene) blended with nonconjugated bisphthalimides were prepared. Upon visible-light excitation of the dyes, quenching of the excited state occurs by exciplex formation between dye and bisphthalimide molecules or, in some cases, by excimer formation or aggregation-induced emission between two dye molecules. The extent of exciplex formation is dependent on the driving force, which can be calculated using the energy difference between the lowest unoccupied molecular orbitals (LUMOs) of the dyes and bisphthalimides. The results show that complete exciplex formation occurs when this driving force is greater than 0.57 eV whereas partial exciplex formation occurs when the driving force is between 0.28 and 0.57 eV. The exciplex emission energies can also be predicted by calculating the difference between the LUMO level of the bisphthalimide and the highest occupied molecular orbital (HOMO) of the dye. These calculated values, which were obtained from the electrochemically determined energy levels, showed good agreement with the observed emission energies. The exciplex lifetimes were found to be significantly longer than the lifetimes of the lone dyes. These exciplexes formed from nonlinked donors and acceptors in the solid state might have potential uses in nonlinear photonics.

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Electrically Tunable, Fully Solid Reflective Optical Elements

Phillips

Schlafmann

Fowler

et al. 2022

Advanced Optical Materials

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or left-hand circular polarized (LHP) depending on the enantiomeric handedness of the chiral dopant, resulting in a 50% reflection efficiency.Numerous prior investigations have examined the electro-optic reconfiguration of the CLC phase. [8][9][10][11] Application of an electric field to a CLC phase with positive dielectric anisotropy in the planar alignment (reflective state) causes the material to transition to a homeotropic orientation (clear state). [9] However, the recovery of the CLC phase from the electrically induced homeotropic orientation can take many days and often results in the formation of a so-called focal conic texture (optically scattering). Yang first detailed the use of polymer stabilization of the CLC phase (PSCLC) as an approach to expedite the recovery of the reflective state after electro-optic switching. [12,13] Recent reports detail the use of polymer stabilization to realize tuning or broadening the selective reflection of PSCLCs. [10,11,[14][15][16][17] Direct electro-optic reconfiguration of the CLC phase has been reported recently in compositions prepared with so-called twistbend nematics, with high bend Frank elastic constant values. [18] While low molar mass liquid crystals are pervasive in the displays of consumer electronics held in purses, pockets, and adorning the walls of our homes -these materials have some drawbacks in certain implementations. Although electro-optic liquid crystalline devices can be prepared on flexible substrates, great care must be taken to protect the device from shorting via electrode contact. Dynamic reconfiguration of the reflection of an optical element has also been explored in polymeric compositions that are amenable to stimuli-response. The reflective character has been retained in polymeric materials including block copolymers, [19] photonic crystals, [20] and inverse opal structures. [21] The selective reflection of these polymeric optical materials can be reconfigured via mechanical deformation, or in some cases, by sensitizing the periodic medium to electrical field or light.Toward this end, we are concerned with the realization of electrically tunable and fully solid liquid crystalline elements. Critical to this realization is the retention of the CLC phase in a lightly crosslinked polymer network capable of dynamic optical reconfiguration. Such cholesteric liquid crystalline elastomers (CLCEs) have been prepared by single and multi-step polymerization reactions. Optical quality has proved difficult to achieve in either case. This quality is dictated by the homogeneity and alignment of the helical pitch which propagates through the thickness of the material. Multiple approaches aimed at improving helical alignment have been demonstrated, albeit to varying degrees of success. Historically, alignment methods have evolved from anisotropic deswelling and Electrochromic devices have seen widespread adoption in the automotive and aerospace industries and are increasingly considered for applications in the built environment, such as smart windows. He...

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Exciplex formation in solid state blends of charge-transfer type AFX dyes and bisimide compounds

Cited by 3 publications

References 16 publications

Symmetry- and Solvent-Dependent Photophysics of Fluorenes Containing Donor and Acceptor Groups

Symmetry- and Solvent-Dependent Photophysics of Fluorenes Containing Donor and Acceptor Groups

Exciplex Formation in Blended Spin-Cast Films of Fluorene-Linked Dyes and Bisphthalimide Quenchers

Electrically Tunable, Fully Solid Reflective Optical Elements

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