Effects of (Multi)branching of Dipolar Chromophores on Photophysical Properties and Two-Photon Absorption

Abstract

To investigate the effect of branching on linear and nonlinear optical properties, a specific series of chromophores, epitome of (multi)branched dipoles, has been thoroughly explored by a combined theoretical and experimental approach. Excited-state structure calculations based on quantum-chemical techniques (timedependent density functional theory) as well as a Frenkel exciton model nicely complement experimental photoluminescence and one-and two-photon absorption findings and contribute to their interpretation. This allowed us to get a deep insight into the nature of fundamental excited-state dynamics and the nonlinear optical (NLO) response involved. Both experiment and theory reveal that a multidimensional intramolecular charge transfer takes place from the donating moiety to the periphery of the branched molecules upon excitation, while fluorescence stems from an excited state localized on one of the dipolar branches. Branching is also observed to lead to cooperative enhancement of two-photon absorption (TPA) while maintaining high fluorescence quantum yield, thanks to localization of the emitting state. The comparison between results obtained in the Frenkel exciton scheme and ab initio results suggests the coherent coupling between branches as one of the possible mechanisms for the observed enhancement. New strategies for the rational design of NLO molecular assemblies are thus inferred on the basis of the acquired insights.

2-Arylvinylpyrimidines versus 4-arylvinylpyrimidines: synthesis and comparison of the optical properties

“…This solvatochromic behavior, which results from the stabilization of the highly polar emitting state by polar solvents, is typical for compounds exhibiting an internal charge transfer upon excitation and has been fully documented with donor-acceptor fluorophores. 18 When comparing for each substituent the emission solvatochromic range expressed as a wave number for 2-arylvinylpyrimidines 5 and 4-arylvinylpyrimidines 6, it appears that this range is much higher for compounds 5 than for compounds 6. Moreover the slope of the emission maxima versus E T (30) is higher for 2-arylvinylpyrimidine 5 than for 2-arylvinylpyrimidine 6 for each substituent.…”

Dynamic quenching of porphyrin triplet states by two-photon absorbing dyes: Towards two-photon-enhanced oxygen nanosensors

“…Dyes C and D were synthesized using the method described by Blanchard-Desce et al [23] and Ulman et al [24] with minor modifications. Dyes B, [24] E [1] and F [25] were prepared as described previously.…”

Two-Photon Transitions in Quadrupolar and Branched Chromophores: Experiment and Theory

“…58,72 Indeed, the optical properties of multimeric dipolar chromophores can be either comparable 72 or significantly different 63 from those observed for their monomeric analogues. When dipolar branches are connected via an ambivalent (i.e., able to act either as a weak electron donor or a weak electron acceptor) triphenylbenzene (TPBenzene) core, it has been shown that the dipolar branches behave nearly as independent subchromophores.…”

“…Analysis of the results of recent studies of the TPA properties of a series of branched chromophores built from the gathering of dipolar sub-chromophores via a common electroactive core moiety demonstrates that the TPA properties can be significantly affected by varying the connecting unit 63,72 or the conjugated branch length. 58,72 Indeed, the optical properties of multimeric dipolar chromophores can be either comparable 72 or significantly different 63 from those observed for their monomeric analogues.…”

“…Interestingly, while only electrostatic interactions appear to contribute to the interbranch coupling in the case of multimeric systems built from a TPBenzene core (leading to weak TPA enhancement), 72 other sources of couplings such as coherent interactions can be present when a TPAmine moiety is used as the branching unit. 62,63,71 Interestingly, both branched systems built from a TPBenzene or TPAmine core were shown to lead to strongly dipolar emitting excited states as a result of the localization of the excitation on a single dipolar branch. 63,71,72 It should be noted that experimental evidence of the localization of the excitation on a single branch prior to emission has been given for various branched systems built from a TPBenzene core.…”