TY  - JOUR
A1  - Dey, Somnath
A1  - Schönleber, Andreas
A1  - Smaalen, Sander van
A1  - Morgenroth, Wolfgang
A1  - Larsen, Finn Krebs
T1  - Incommensurate phase in Λ-cobalt (III) sepulchrate trinitrate governed by highly competitive N-H...O and C-H...O hydrogen bond networks
JF  - Chemistry - a European journal
N2  - Phase transitions in molecular crystals are often determined by intermolecular interactions. The cage complex of [Co(C12H30N8)](3+) . 3 NO3- is reported to undergo a disorder-order phase transition at T-c1 approximate to 133 K upon cooling. Temperature-dependent neutron and synchrotron diffraction experiments revealed satellite reflections in addition to main reflections in the diffraction patterns below T-c1. The modulation wave vector varies as function of temperature and locks in at T-c3 approximate to 98 K. Here, we demonstrate that the crystal symmetry lowers from hexagonal to monoclinic in the incommensurately modulated phases in T-c1<T<T-c3. Distinctive levels of competitions: trade-off between longer N-H...O and shorter C-H...O hydrogen bonds; steric constraints to dense C-H...O bonds give rise to pronounced modulation of the basic structure. Severely frustrated crystal packing in the incommensurate phase is precursor to optimal balance of intermolecular interactions in the lock-in phase.
KW  - hydrogen bond
KW  - incommensurate modulation
KW  - phase transition
KW  - steric factors
KW  - twin domains
Y1  - 2022
U6  - https://doi.org/10.1002/chem.202104151
SN  - 0947-6539
SN  - 1521-3765
VL  - 28
IS  - 13
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - García-Benito, Inés
A1  - Quarti, Claudio
A1  - Queloz, Valentin I. E.
A1  - Hofstetter, Yvonne J.
A1  - Becker-Koch, David
A1  - Caprioglio, Pietro
A1  - Neher, Dieter
A1  - Orlandi, Simonetta
A1  - Cavazzini, Marco
A1  - Pozzi, Gianluca
A1  - Even, Jacky
A1  - Nazeeruddin, Mohammad Khaja
A1  - Vaynzof, Yana
A1  - Grancini, Giulia
T1  - Fluorination of organic spacer impacts on the structural and optical response of 2D perovskites
JF  - Frontiers in Chemistry
N2  - Low-dimensional hybrid perovskites have triggered significant research interest due to their intrinsically tunable optoelectronic properties and technologically relevant material stability. In particular, the role of the organic spacer on the inherent structural and optical features in two-dimensional (2D) perovskites is paramount for material optimization. To obtain a deeper understanding of the relationship between spacers and the corresponding 2D perovskite film properties, we explore the influence of the partial substitution of hydrogen atoms by fluorine in an alkylammonium organic cation, resulting in (Lc)(2)PbI4 and (Lf)(2)PbI4 2D perovskites, respectively. Consequently, optical analysis reveals a clear 0.2 eV blue-shift in the excitonic position at room temperature. This result can be mainly attributed to a band gap opening, with negligible effects on the exciton binding energy. According to Density Functional Theory (DFT) calculations, the band gap increases due to a larger distortion of the structure that decreases the atomic overlap of the wavefunctions and correspondingly bandwidth of the valence and conduction bands. In addition, fluorination impacts the structural rigidity of the 2D perovskite, resulting in a stable structure at room temperature and the absence of phase transitions at a low temperature, in contrast to the widely reported polymorphism in some non-fluorinated materials that exhibit such a phase transition. This indicates that a small perturbation in the material structure can strongly influence the overall structural stability and related phase transition of 2D perovskites, making them more robust to any phase change. This work provides key information on how the fluorine content in organic spacer influence the structural distortion of 2D perovskites and their optical properties which possess remarkable importance for future optoelectronic applications, for instance in the field of light-emitting devices or sensors.
KW  - fluorinated organic spacer
KW  - 2D perovskites
KW  - phase transition
KW  - temperature dependence
KW  - excitonic materials
Y1  - 2020
U6  - https://doi.org/10.3389/fchem.2019.00946
SN  - 2296-2646
VL  - 7
SP  - 1
EP  - 11
PB  - Frontiers Media
CY  - Lausanne
ER  - 
TY  - JOUR
A1  - Henkel, Carsten
A1  - Sauer, Tim-O
A1  - Proukakis, N. P.
T1  - Cross-over to quasi-condensation: mean-field theories and beyond
JF  - Journal of physics : B, Atomic, molecular and optical physics
N2  - We analyze the cross-over of a homogeneous, weakly interacting Bose gas in one dimension from the ideal gas into the dense quasi-condensate phase. We review a number of mean-field theories, perturbative or self-consistent, and provide accurate evaluations of equation of state, density fluctuations, and correlation functions. A smooth crossover is reproduced by classical-field simulations based on the stochastic Gross-Pitaevskii equation and the Yang-Yang solution to the one-dimensional Bose gas.
KW  - quantum gases
KW  - Bose-Einstein condensation
KW  - phase transition
KW  - critical fluctuations
Y1  - 2017
U6  - https://doi.org/10.1088/1361-6455/aa6888
SN  - 0953-4075
SN  - 1361-6455
VL  - 50
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  -