| 1. |
- Knaapila, Matti, et al.
(författare)
-
Meridional orientation in biaxially aligned thin films of hairy-rod polyfluorene
- 2007
-
Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 7:9, s. 1706-1711
-
Tidskriftsartikel (refereegranskat)abstract
- The uniaxial chain alignment and equatorial patterning of poly [9,9-bis(2-ethylhexyl)fluorene-2,7-diyl] (M-n = 29 kg/mol, M-w = 68 kg/mol) thin films atop rubbed polyimide substrates have been studied by grazing incidence X-ray diffraction. This specific molecular weight yields among the highest observed levels of chain alignment and optical anisotropy and, after thermal annealing, the sample undergoes transformation to a highly textured crystalline hexagonal phase. The two dominant equatorial orientations (i.e., types I and II crystallites) are found to have almost identical meridional orientation distributions. The X-ray deduced orientation is in quantitative agreement with that obtained by optical absorption measurements. It is also shown that the equatorial ordering is paracrystalline in nature, and both type I and type II crystallites are similar in this respect. This equatorial scattering is superimposed on a background of a hexagonal phase polymer with a cylindrically isotropic orientation (type III).
|
|
| 2. |
- Knaapila, Matti, et al.
(författare)
-
Evidence for 21-helicity of poly[9,9-bis(2-ethylhexyl)fluorene-2,7-diyl]
- 2007
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 40:10, s. 3610-3614
-
Tidskriftsartikel (refereegranskat)abstract
- The conformational state of the pi-conjugated polyfluorene poly[9,9-bis(2-ethylhexyl)fluorene-2,7-diyl] is reconsidered. Contrary to the general opinion, this helical polymer is shown to organize in a giant repeat consisting of 21 monomer units. The length of the unit cell of 16.97 nm is suggested.
|
|
| 3. |
- Morozov, Konstantin M., et al.
(författare)
-
Efficient UV Luminescence from Organic-Based Tamm Plasmon Structures Emitting in the Strong-Coupling Regime
- 2020
-
Ingår i: The Journal of Physical Chemistry C. - : AMER CHEMICAL SOC. - 1932-7447 .- 1932-7455. ; 124:39, s. 21656-21663
-
Tidskriftsartikel (refereegranskat)abstract
- Excitons in organic semiconductors possessing a large oscillator strength demonstrate strong coupling with cavity modes at room temperature. A large Stokes shift in some organic semiconductors enriches and complicates the picture of the emission in strongly coupled systems of organic excitons and light. Here, we demonstrate strong coupling of excitons in 4,4-bis(N-carbazolyl)-1,1-biphenyl (CBP) and Tamm plasmons in the ultraviolet (UV) band, accompanied by a bright emission from the structure. Reflection measurements demonstrate the pronounced formation of the lower and upper polariton modes with Rabi splitting of the magnitude of 0.3 eV, and the emission peak experiences a substantial red shift with respect to the lower polariton mode. Both radiative and nonradiative decay rates in the Tamm plasmon CBP structure are increased with respect to a bare CBP. Such peculiar behavior is attributed to the simultaneous manifestation of strong coupling and weak coupling of the CBP molecule emitters to the Tamm plasmons.
|
|
| 4. |
- Morozov, Konstantin M., et al.
(författare)
-
Opposite Sign of Polarization Splitting in Ultrastrongly Coupled Organic Tamm Plasmon Structures
- 2021
-
Ingår i: The Journal of Physical Chemistry C. - : AMER CHEMICAL SOC. - 1932-7447 .- 1932-7455. ; 125:15, s. 8376-8381
-
Tidskriftsartikel (refereegranskat)abstract
- The properties of the ultrastrongly coupled Tamm plasmon cavity filled with a high-oscillator-strength organic material DPAVBi (4,4-bis[4-(di-p-tolylamino)styryl]biphenyl) are studied using theoretical and experimental methods. An analytical model predicts the opposite sign of polarization splitting for the lower and upper polariton cases and a giant absolute value of the splitting. A set of organic Tamm plasmon cavities with different detuning parameters are fabricated. We demonstrate that all structures are operating in the ultrastrong coupling regime: the values of the Rabi splitting are close to a 20% fraction of the exciton energy. The measured angle-dependent reflectivity spectra structure for both transverse electric (TE) and transverse magnetic (TM) polarizations confirm the predicted theoretical model. We obtained a giant value of the polarization splitting of up to 180 meV for both polariton branches. We believe that it is the first demonstration of such peculiar polarization splitting behavior of polaritons in the ultrastrong coupling regime.
|
|
| 5. |
- Morozov, Konstantin M., et al.
(författare)
-
Revising of the Purcell effect in periodic metal-dielectric structures: the role of absorption
- 2019
-
Ingår i: Scientific Reports. - : NATURE PUBLISHING GROUP. - 2045-2322. ; 9
-
Tidskriftsartikel (refereegranskat)abstract
- Periodic metal-dielectric structures attract substantial interest since it was previously proposed that the spontaneous emission amplification rates (the Purcell factor) in such structures can reach enormous values up to 105. However, the role of absorption in real metals has not been thoroughly considered. We provide a theoretical analysis showing that absorption leads to diminishing values of Purcell factor. We also suggest that using emitting organic compounds such as CBP (4,4-Bis(N-carbazolyl)-1,1-biphenyl) can lead to a moderate increase of about an order of magnitude in the Purcell factor. Defining the experimentally measured Purcell factor as a ratio between the excited state lifetimes in bare CBP and in periodic structure, this increase in the fabricated periodic structure is demonstrated through a 4-8 times decrease in excited state radiative lifetime compared to a bare organic material in a wide emission spectrum.
|
|
