Nonlinear Optical Properties of Bis(dehydrobenzoannuleno)benzenes: An Experimental and Computational Approach

Given their molecular properties and electronic structure, graphyne and graphdiyne are promising materials with numerous applications in different fields of material science. Dehydrobenzoannules (DBAs) are candidates that can serve as building blocks for synthesizing and designing new 2D carbon allotropes; however, only a few graphynes have been produced on a practical scale. Herein, we present our investigation of three DBAs, which serve as a model to understand the relationship between the structure and property, contributing to 2D carbon allotropes' rational design and synthetic effort. We performed entangled and classical two-photon absorption at 790 nm, revealing that minor structural changes within acetylenic units significantly impact the magnitudes of the entangled and classical two-photon cross sections. Later, we deconvolved the excited-state dynamics through femtosecond transient absorption, and the lifetimes on the nanosecond time scale were measured using time-correlated single-photon counting. Finally, electronic structure calculations were performed to compute the oscillator strength and energy associated with electronic transitions between the ground and excited states and among the excited states. The results reveal that the remarkable difference in nonlinear optical properties among the DBAs, despite their structural similarities, stems from the transition dipole moment associated with transitions among excited states.