The fluorescent molecule diphenylhexatriene (DPH) has been often used in combination with fluorescence anisotropy measurements, yet little is known regarding the non-linear optical properties. In the current work, we focus on them and extend the application to fluorescence, while paying attention to the conformational versatility of DPH when it is embedded in different membrane phases. Extensive hybrid quantum mechanics/molecular mechanics calculations were performed to investigate the influence of the phase- and temperature-dependent lipid environment on the probe. Already, the transition dipole moments and one-photon absorption spectra obtained in the liquid ordered mixture of sphingomyelin (SM)-cholesterol (Chol) (2:1) differ largely from the ones calculated in the liquid disordered DOPC and solid gel DPPC membranes. Throughout the work, the molecular conformation in SM:Chol is found to differ from the other environments. The two-photon absorption spectra and the ones obtained by hyper-Rayleigh scattering depend strongly on the environment. Finally, a stringent comparison of the fluorescence anisotropy decay and the fluorescence lifetime confirm the use of DPH to gain information upon the surrounding lipids and lipid phases. DPH might thus open the possibility to detect and analyze different biological environments based on its absorption and emission properties.

Chemical and Biological Systems Simulation Lab Centre of New Technologies University of Warsaw Banacha 2c 02 097 Warsaw Poland

Department of Theoretical Chemistry and Biology School of Engineering Sciences in Chemistry Biotechnology and Health KTH Royal Institute of Technology SE 10691 Stockholm Sweden

Regional Centre of Advanced Technologies and Materials Department of Physical Chemistry Faculty of Science Palacký University Olomouc 17 listopadu 12 771 46 Olomouc Czech Republic

Theory Lab Hasselt University Agoralaan Building D 3590 Diepenbeek Belgium

References provided by Crossref.org