Chiroptical properties of helical-shaped π-conjugated systems based on five- and six-membered rings

Abstract

quotThis thesis talks about structure-property relations and excited-states properties including chiroptical properties of screw-shaped and#960;-conjugated systems. Helical-shaped systems are inherently chiral due to newlinetheir helical motifs. They have large applications in the various fields material chemistry such as, in organic newlinelight emitting diode, perovskite solar cell, bioimaging, fluorescent sensors, asymmetric synthesis etc.. In newlinerecent times, a large number of helical shaped systems have been developed and helicenes are widely studied examples of them. However, this thesis mainly focuses on absorption, circular dichroism (CD), and newlinecircularly polarised luminescence (CPL) properties studied in different levels of theories. Widely used pristine helicenes possess lower values of fluorescence quantum yield (and#934;FL) and dissymmetry factor for newlineemission (gCPL). Literature shows that designing of light-emitting molecules with higher values of and#934;FL and gCPL is not an easy task. In recent times, various types of modified helical structures including multiple helicenes are reported. In case of single-helicenes, typical modifications are based on either increasing the number of and#960;-conjugated rings (i.e., either helical length or lateral extension) or substitution of hydrogen atoms by other functionals groups. At this juncture, computational studies are very useful for studying and newlinedesigning molecules with improved chiroptical properties. In this thesis, excited-states properties of screwshaped newlinepyridine-thiophene oligomers and various helicenes are reported. Effects of helical/lateral length extension and fluorine substitution on the ground and excited state properties are reported. The performance of these systems towards photoluminescence applications are measured by some key newlineparameters, such as rotatory strength, gCPL, and and#934;FL. Methods such as Density Functional Theory (DFT), time-dependent DFT (TD-DFT) and wavefunction based algebraic diagrammatic construction scheme of second order (ADC(2)) are used in these studiesquot newline