Phase Transitions and Structures of Novel Pyrenes Potentially Useful in Photovoltaic Applications

Abstract

A series of conjugated compounds, 6,7,15,16-tetrakis(alkylthio)quinoxalino[2',3':9,10]phenanthro[4,5-abc]phenazine (TQPP-[SC(n)](4)) (n = 6, 8, 10, and 12), which display p-channel characteristics was synthesized. These materials show promise for use in liquid crystalline photovoltaic applications. To determine their applicability, the different phase structures and transitions of these compounds were studied with differential scanning calorimetry (DSC), polarized light microscopy (PLM), wide-angle X-ray diffraction (WAXD), selected area electron diffraction (SAED), and Fourier transform infrared spectroscopy (FT-IR). Using TQPP-[SC(12)](4) as a model compound, DSC and 1D WAXD results showed that this compound possesses four crystalline, but no liquid crystalline, phases. Based on structural results obtained from 2D WAXD experiments on oriented samples and SAED patterns from single crystals, the unit cell of the lowest temperature TQPP-[SC(12)](4) crystalline phase (K(1)) was determined to be monoclinic with dimensions of a = 1.87 nm, b = 0.53 nm, c = 3.51 nm, and beta = 96.2 degrees . With increasing temperature, the K(1) phase transformed to other crystalline phases which all were monoclinic with different crystallographic parameters. The arrangement of the TQPP-[SC(12)](4) rigid fused rings changed only slightly in these crystalline phases, yet the conformation of the alkyl chains attached to the rigid cores changed significantly at the phase transitions. For the other TQPP-[SC(n)](4) compounds, only two phase transitions could be identified. It was determined that the transition temperature can be tuned by modifying the attached alkyl chains at the four corners of the rigid fused rings. One-dimensional WAXD studies indicated that the condensed state phase transitions of these compounds were all crystal-crystal transitions. Although single crystals will provide the highest charge carrier mobility, they are very difficult to grow and incur a high cost in production. On the other hand, liquid crystalline phases are preferred for the ease of processing and reasonable performance in change carrier mobility. Therefore, in order to achieve liquid crystalline phases in these compounds, as desired for their application as organic photovoltaic materials, additional modifications to the alkyl chains and their locations are necessary.

Hierarchical superstructures from a star-shaped molecule consisting of a cyclic oligosiloxane with cyanobiphenyl moieties

“…From the POM analysis, it is found that the transition at elevated temperature is associated with liquid crystal (LC)-isotropic melt (I) transition of the SiLC. 14 The fast cooled SiLC reveals a glassy LC phase below T g ¼ 22 C.…”

Synthesis and aggregation properties of a series of dumbbell polyhedral oligosilsesquioxane-perylene diimide triads

“…The effects of bulky substituents and branched alkyl tails on the modification of phase structures and molecular packing have been nicely illustrated by previous studies. 42,43 Polyhedral oligosilsesquioxanes (POSSs), regarded as small inorganic nanoparticles with diameters up to 1.5 nm, 44 were chosen as the bulky group because of their well-defined nature. The incorporation of POSS into organic molecules can bring remarkable improvement in the thermal and oxidative stability.…”

A supramolecular structure with an alternating arrangement of donors and acceptors constructed by a trans-di-C60-substituted Zn porphyrin derivative in the solid state

“…This metastable phase melts, in the subsequent heating, at 152 C with an identical heat of transition, revealing that the metastable phase is a liquid crystal-like phase for which the transition usually does not exhibit supercooling in transition temperature. 14,17 Formation of the stable phase requires long thermal annealing, such as annealing the metastable phase at 145 C for 3 days.…”

“…[1][2][3][4] Combining p-type and n-type p-conjugated molecules enables the photo-induced charge generation process and provide functions in applications such as photovoltaics and artificial photosynthesis. [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] In particular, using self-assembly to construct supramolecular structures of these p-conjugated molecules has been recognized as an important approach to generate ''supramolecular electronics''. [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39] Research using [60]fullerene (C 60 ) as an electron acceptor (A) and porphyrin as an electron donor (D) has been extensively carried out.…”