Synthesis, Fluorescence, and Two‐Photon Absorption of a Series of Elongated Rodlike and Banana‐Shaped Quadrupolar Fluorophores: A Comprehensive Study of Structure–Property Relationships

Abstract

An extensive series of push-push and pull-pull derivatives was prepared from the symmetrical functionalization of an ambivalent core with conjugated rods made from arylenevinylene or arylene-ethynylene building blocks, bearing different acceptor or donor endgroups. Their absorption and photoluminescence as well as their two-photon absorption (TPA) properties in the near infrared (NIR) region have been systematically investigated in order to derive structure-property relationships and lay the guidelines for both spectral tuning and amplification of molecular TPA in the target region. Whatever the nature of the core or of the connectors, push-push systems were found to be more efficient than pull-pull systems and planarization of the core (fluorene vs biphenyl) always leads to an increase of the TPA crosssections. At contrary, increasing the conjugation length as well as replacement of a phenylene moiety by a thienylene moiety in the conjugated rods did not necessarily lead to increased TPA responses. The present study also demonstrated that the topology of the conjugated rods can dramatically influence the TPA properties. This is of particular interest in terms of molecular engineering for specific applications since both TPA properties and photoluminescence characteristics can be considerably affected. It thus becomes possible to optimize the transparency/TPA and fluorescence/TPA efficiency trade-offs, for optical limiting in the red-NIR region (700-900 nm) and TPEF microscopy applications, respectively.

Charge Instability in Quadrupolar Chromophores: Symmetry Breaking and Solvatochromism

“…77 . The squarine dye 3 was synthesized from squaric acid and corresponding methylene base, using similar experimental conditions as reported in Ref.…”

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

“…A large body of experimental data is available for many families of quadrupolar systems. [3,33,36,57,58,63,76,78,81,85,86,[89][90][91][92][93][94][95][96][97][98][99][100][101][102][103][104][105][106][107] Their nonlinear response is a non-trivial function of terminal donor and acceptor strength, π-conjugated bridge length and type, nature of the conjugated core, torsional disorder, symmetry and topology. [58] In this subsection we exemplify some of these relationships using two different families of quadrupoles to derive general trends in terms of TPA cross sections and peak positions.…”

“…Thereby, attention has progressively moved from the well-known push-pull dipolar molecular structures [34,41,[75][76][77][78][79][80][81][82][83][84][85][86][87][88] to quadrupoles [3,33,36,57,58,63,76,78,81,85,86,[89][90][91][92][93][94][95][96][97][98][99][100][101][102][103][104][105][106][107] and, more recently, toward complex molecular architectures. Quadrupoles have been found to be more efficient than dipoles in terms of TPA, in particular for multiphoton-based opticallimiting applications.…”

An internal charge transfer-dependent solvent effect in V-shaped azacyanines

“…In particular, it was found that the ethylene linker ensures improved conjugation between various parts of the molecule leading typically to a stronger bathochromic shift, a larger two-photon absorption cross-section and higher quantum yields. 28,29 In our case however, the comparison of optical properties of dyes 4 and 5 reveals that both their absorption and emission are bathochromically shifted versus those of their analogues bearing the C-C double bond 23 (Table 1). The effect of solvent polarity on the emission intensity is also profound.…”