Invited webinar - New electrically and optically active molecular materials...- by Giulia Pancotti

"New electrically and optically active molecular materials characterized by synchrotron Circular Dichroism" presented by Giulia Pancotti, Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Spain;  Chaired by Dr. Sara Battista, Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Spain

The phenomenon known as “supramolecular chirality”, whereby the optical properties of a chiral object are transferred, in some extents, to higher order supramolecular structures, is of particular interest in the development of organic photovoltaic devices (OPVs). Thin films exhibit a close relationship between their supramolecular arrangement and their efficiencies, thereby highlighting the significant role played by the correlation between the chiral supramolecular arrangement and the physical parameters of the devices such as Fill Factor (FF), Open Circuit Voltage (Voc) and Short Circuit Current (Isc).

Additionally, chirality provides the opporunity to employ Circular Dicroism (CD) spectroscopy to employ Circular Dichroism (CD) spectroscopy, which is the preferred method for investigating optical activity . CD spectra have the advantage to be higly sensitive to changes in supramolecular structure, making them uniquely capable of providing valuable insights into the conformational changes that occur in both natural and synthetic materials.

The focus of our project is centered on the synthesis of new enantiomerically pure DPP dyes that exhibit high absorbance and excellent photostability. These dyes are intended for use as the active layer in photovoltaic devices, in conjunction with ITIC-4F acceptor. A key objective of our research is to develop an understanding of the relationship between the supramolecular structure of DPPs and their efficiency in electron transfer.

To achieve this goal, we have employed CD studies in the solid state, using the B23 beamline at the Diamond Light Source Synchrotron. This approach involves analysing thin films of chiral materials to obtain a Mueller Matrix Plot (MMP), which enables us to accurately measure the CD spectrum in solid state, without being misled by linear anisotropies, such linear dichroism or linear birefringence. Those techniques allow us to gain a better understanding of the properties of these materials and their potential use in photovoltaic applications.

(1)  First, A.; Second, B.; Third, C. J. Am. Chem. Soc.  2018, 138, 1.

(2)  First, A.; Second, B.; Third, C. J. Am. Chem. Soc.  2018, 138, 10.

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