Ultrafast Dynamics in Multibranched Structures with Enhanced Two-Photon Absorption

Abstract

The understanding of the mechanism of the enhanced two-photon absorption (TPA) in multibranched chromophore systems is of importance to the design of materials with the large TPA cross-sections and for future applications. In this communication, the mechanism of enhanced TPA properties is investigated. For a dendritic model system, the excited-state dynamics for both population (T1-process) and phase relaxation (T2-process) processes involved are investigated by a combination of time-resolved spectroscopic techniques. The results of time-resolved fluorescence anisotropy are compared with previous results obtained from other branched chromophore systems. It is found that the PRL-701 trimer system, which possesses the large enhancement of two-photon absorption cross-section, gives a faster anisotropy decay (fluorescence upconversion and transient absorption), a longer population relaxation time (fluorescence lifetime), and a weaker coupling to the solvent (a larger photon echo peak shift initial value). New strategies for rational design of large TPA materials can be achieved based on a better understanding of the mechanism of the enhancement.

Linear and Two‐Photon Absorption Properties of Interacting Polar Chromophores: Standard and Unconventional Effects

“…However, relaxation of nuclear and solvation degrees of freedom after absorption and prior to fluorescence guides the system toward a more localised state. This phenomenon has already been observed for multibranched systems in which subchromophores are linked so as to allow conjugation to extend from one subunit to another, [36,53,54] and for covalent dimers in which orbitals of subunits strongly overlap through p stacking. [55] Localisation phenomena involving multichromophore systems are also of fundamental importance in the complicated systems of light-harvesting complexes where the trap-ping process is thought to involve the whole photosynthetic unit.…”

Enhanced Two‐Photon Absorption of Organic Chromophores: Theoretical and Experimental Assessments

“…[120,121,289,290] However, in all branched fluorophores, fluorescence stems from a single branch. [120,121,123,142,289,290,[292][293][294][295][296] This phenomenon of localization of excitation seems to be a general characteristic of branched systems.…”

Charge Instability in Quadrupolar Chromophores: Symmetry Breaking and Solvatochromism

“…A large body of experimental data is available for many families of quadrupolar 5,7,[9][10][11]13,18,[33][34][35][36] and octupolar chromophores 15,17,18,34,[37][38][39][40][41][42][43][44][45] as well as for branched and dendritic systems. 16,40,43,44,46,47 Due to their highly symmetric structure, all these systems have no permanent dipole moment and of course vertical (unrelaxed) states are non-dipolar as well.…”