Design rules for the large two-photon absorption diketopyrrolopyrrole-based quadrupolar symmetrical chromophores

A Modified Oxazolone Dye Dedicated to Spectroscopy and Optoelectronics

Here we present a newly synthesized bifunctional organic chromophore with appealing spectroscopic and nonlinear optical features. The positions of absorption and emission maxima of the dye vary with increasing solvent polarity and exhibit positive solvatochromism. The determined change in the dipole moment upon excitation based on the Bilot and Kawski theory is 5.94 D, which corresponds to the intermolecular displacement of a charge equal to 1.24 Å. An investigated organic-based system represents a significant, repeatable, and stable over time optical signal modulation in the manner of the refractive index value. Its magnitude is varied both by optical pumping intensity as well as by external frequency modulation, which indicates that such system is an alluring and alternative core unit for optoelectronic devices and complex networks. Then, the same active system, due to the nonresonant mechanism of higher harmonics of light inducement, can provide second and third harmonic signals. According to the introduced laser line spatial modifications (parallel or perpendicular polarization directions), it is resulted in output SHG signal with magnitude varied about 100%. Its magnitude is noticeably small; however, to construct sensitive optical sensors or infrared indicators, such feature may guarantee satisfying circumstances.

Effect of Polymerization on the Charge-Transfer Mechanism in the One (Two)-Photon Absorption Process of D-A-Type Triphenylamine Derivatives

To investigate the effect of polymerization (n = 1, 2, 3, and 4) on the charge-transfer (CT) mechanisms in the one (two)-photon absorption (OPA and TPA) process of D-A-type triphenylamine derivatives, charge density difference is used to graphically represent the CT characteristics. A transition density matrix is utilized to reveal the direction of CT on different groups quantitatively. With the n increasing, electrons are mainly transferred between the groups in the middle position of the molecular chain during OPA and TPA processes. Simulated results show that the energy gap and excitation energy have a good linear relationship with the reciprocal of the polymerization degree. Importantly, the polymerization effect can effectively increase the electronic transmission capability, TPA performance, and second hyperpolarizability. Besides, the simplified sum over state model reveals the variation factor of the TPA cross-section and the second static hyperpolarizability. The McRae formula and Bakhshiev formula are used to estimate the difference of dipole moments, which is an important parameter of the second hyperpolarizability. The comprehensive analysis of the nonlinear optical (NLO) parameters of triphenylamine derivatives can provide some significant guidance for molecular design and improve the NLO performance of D-A molecular materials. Also, the thermodynamic parameters can provide some theoretical supports for solving practical problems.