Twisted Intramolecular Charge Transfer States in Trinary Star-Shaped Triphenylamine-Based Compounds

Abstract

Excited state dynamics of trinary star-shaped dendritic compounds with triphenylamine arms and different cores were studied by means of time-resolved fluorescence and transient absorption. Under optical excitation, nonpolar C symmetry molecules form polar excited states localized on one of the molecular substituents. Conformational excited state stabilization of molecules with an electron-accepting core causes a formation of twisted internal charge transfer (TICT) states in polar solvents. A low transition dipole moment from TICT state to the ground state causes very weak fluorescence of those compounds and strong dependence on the solvent polarity. The compound formed from the triphenylamine central core and identical arms also experiences excited state twisting, however, weakly sensitive to the solvent polarity.

Temperature-Controlled Locally Excited and Twisted Intramolecular Charge-Transfer State-Dependent Fluorescence Switching in Triphenylamine–Benzothiazole Derivatives

“…The nonplanar molecular conformation of triphenylamine (TPA) and tetraphenyl ethylene core has been used to generate aggregation-enhanced emissive (AEE) and stimuli-responsive fluorescent materials. 5−7 Conformational flexibility of fluorophores produced polymorphism-induced fluorescence switching and tuning. 8−10 Donor–acceptor (D–A) organic molecules display locally excited (LE) and twisted intramolecular charge-transfer (TICT) state fluorescence depending on the solvent polarity and viscosity that drastically modulated the fluorescence λ max and efficiency.…”

“…Fluorescence switching and tuning of organic molecules received significant attention over the years because of their fundamental importance and application potentials in modern optical and optoelectronic devices. − Fluorescence phenomena that involve electron transfer, energy transfer, excimer formation, and J or H aggregation have been strongly influenced by fluorophore orientation, conformation, and flexibility. The nonplanar molecular conformation of triphenylamine (TPA) and tetraphenyl ethylene core has been used to generate aggregation-enhanced emissive (AEE) and stimuli-responsive fluorescent materials. − Conformational flexibility of fluorophores produced polymorphism-induced fluorescence switching and tuning. − Donor–acceptor (D–A) organic molecules display locally excited (LE) and twisted intramolecular charge-transfer (TICT) state fluorescence depending on the solvent polarity and viscosity that drastically modulated the fluorescence λ max and efficiency. , Interestingly, the LE and TICT character of D–A molecules can easily be controlled using several factors including steric substituents, conformation, D–A strength, and polarity environments that make the D–A fluorophores highly attractive toward various applications. − Boron–dipyrromethene-based compounds exhibited transition from nonpolarized fluorescent LE state to nonfluorescent highly polarized TICT state depending on the solvent polarity, which has been used as an environmental polarity sensor. , Steric restrictions in D–A molecules enabled precise control of the proportion of the LE and TICT state and are used for developing solvatochromic probes and AEE materials. − …”

Solution‐Processable Unsymmetrical Triarylamines: Towards High Mobility and ON/OFF Ratio in Bottom‐Gated OFETs

“…The compounds exhibit two bands around 260–280 nm attributed to π–π* transition and a more pronounced band around 350 nm; the absorption maximum λ max corresponds to an n–π* transition. Comparison of the optical data of 2 – 8 with those of precursor 1 shows that the introduction of an aryl group with electron‐donating and electron‐withdrawing groups alters the photophysical behavior of the TAAs remarkably . Compound 4 has a redshifted absorption maximum due to the incorporation of highly conjugated biphenyl units in two arms.…”

“…Comparison of the opticald ata of 2-8 with those of precursor 1 shows that the introduction of an aryl group with electron-donating ande lectron-withdrawing groups alters the photophysical behavioro ft he TAAs remarkably. [27] Compound 4 has ar edshifted absorption maximum due to the incorporation of highly conjugated biphenyl units in two arms. Compound 3 has extended naphthalene units and shows a1 2nm bathochromic shift relative to 2 with similar p-p*t ransition.…”

“…Although these compoundsh ave significant dipole moments in the relaxede xcited state, molecular twisting is deceptively decoupled from charge transfer withoutt he helpo fs olvent. [27] In the excited state, excitons are localized in any one of the arms with respect to different conformational changes in the excited states. [29] So, emission spectra of all the new functionalized TAAs are not observed as as ingle sharpp eak.…”