Singlet and triplet energy transfers in tetra-(meso-truxene)zinc(II)- and tetra-(meso-tritruxene)zinc(II) porphyrin and porphyrin-free base dendrimers

Porphyrinoid-Functionalized ZnO Nanoflowers for Visible Light-Enhanced and Selective Benzylamine Detection at Room Temperature

Functionalization of hybrid organic molecules as layers on ZnO nanoflowers (NFs) gives an excellent combination of sensing toward visible light and vapors of various volatile organic compounds (VOCs). In this work, hybrid organic molecules functionalized ZnO NFs were utilized for the photoinduced detection of benzylamine at room temperature. The ZnO NFs were synthesized via a facile solution route and functionalized with four different porphyrin-conjugated molecules namely (i) pyrene-porphyrin (PP), (ii) pyrene- porphyrinato zinc (ZnPP), (iii) triphenylamine- porphyrin (TP) and (iv) triphenylamine- porphyrinato zinc (ZnTP). The diameter of the flower-like structure was found to be ∼3.2 μm with the thickness of petals being ∼24.1 nm. The gas adsorption performance of the functionalized ZnO NFs on light activation at room temperature was studied by using a scanning Kelvin probe (SKP) system. The improved adsorption properties of the samples can be attributed to the heterojunctions and light activation. In particular, an enhanced response of ZnTP functionalized ZnO (ZnTPZ) toward benzylamine was observed. Further, static gas sensing experiments using ZnTPZ under various concentrations (1, 3, 5, 10, 15, and 25 ppm) of benzylamine vapors both in dark and visible light conditions have exhibited a linear increase in the response. The selectively enhanced response of ZnTPZ compared to that of pristine ZnO was thus confirmed at 1 ppm of benzylamine. The sensitivity and limit of detection of the ZnTPZ sensor were calculated to be 0.0292 ppm-1 and 197 ppb, respectively. The coordination metal (Zn) has helped in effective charge transfer between benzylamine and ZnTPZ by providing additional active sites for interactions. Also, density functional theory calculations demonstrated the role of the hybrid organic molecules on the sensor surface in improving gas adsorption. Further, fresh cabbage was utilized for real sample analysis with the proposed sensor under visible light illumination conditions, and a linear response was obtained for low ppm evaluation at room temperature. Overall, the obtained results suggest the development of novel ZnTPZ-based light-activated gas sensors for low ppm benzylamine detection at room temperature. These kinds of sensors can be used to track the freshness of vegetables as they are transported from farms to commercial outlets.

Heavy-Atom-Free Covalent Organic Frameworks for Organic Room-Temperature Phosphorescence via Förster and Dexter Energy Transfer Mechanism

Covalent organic frameworks (COFs), with their accessible nanoscale porosity, selectable building blocks, and precisely engineered topology, offer unique benefits in the design of room-temperature phosphorescent (RTP) materials. However, their potential has been limited by phosphorescence quenching caused by interlayer π-π stacking interactions. This paper presents a novel strategy to enhance RTP in heavy-atom-free COFs by employing a donor-acceptor (D-A) system that leverages the Förster resonance energy transfer (FRET) and Dexter energy transfer (DET) mechanisms. Among the materials investigated, the best-performing COF exhibits a phosphorescence lifetime of 4.35 ms at room temperature. Spectral analysis, structural analysis, and theoretical calculations indicate the presence of intralayer FRET processes as well as interlayer DET processes within the D-A COF system. Potential anti-counterfeiting applications are explored by exploiting the unique phosphorescent properties of these materials. Additionally, the inherent permanent porosity of COFs presents new opportunities for future development and application. This strategy offers many promising prospects for advancing the RTP technology in COF materials and broadens their potential applications in various fields.

Truxene-to-Fluorenone Energy Transfer in a Robust Mesoporous Zn-MOF

A new metal-organic framework (MOF; [Zn4O(hett)4/3(fluo)1/2(bdc)1/2]n; TFT-MOF) constructed on chromophoric ligands 5,5',10,10',15,15'-hexaethyltruxene-2,7,12-triacetate (hett), 9-fluorenone-2,7-dicarboxylate (fluo), terephthalate (bdc), and the Zn4O node has been prepared and identified by powder X-ray diffraction. This luminescent MOF exhibits large mesoporous pores of 2.7 nm based on computer modeling using density functional theory (DFT) calculations. The steady-state and time-resolved fluorescence spectra and photophysical parameters of TFT-MOF have been investigated and compared with those of the free ligands and their basic chromophores. All in all, TFT-MOF exhibits particularly efficient singlet-singlet energy-transfer processes described as 1(hett)* → (fluo) and 1(bdc)* → (fluo), leading to fluorescence arising for the fluo lumophore operating only through Förster resonance energy transfer (FRET) with an efficiency of transfer of up to >95%. This experimental conclusion was corroborated by DFT and time-dependent DFT (TDDFT). For the 1(hett)* → (fluo) process, the approximated overall rate constant of energy transfer was evaluated to be at most 2.04 × 1010 s-1 (using a Stern-Volmer approach of solution data and the relationship between distance and concentration). This process was analyzed using the Förster theory, where two intrapore energy transfer paths of center-to-center distances of 13 and 25 Å have been identified. TFT-MOF photosensitizes the formation of singlet oxygen (1O2 (1Σg)) as detected by its phosphorescence signal at 1275 nm.

From truxenes to heterotruxenes: playing with heteroatoms and the symmetry of molecules

As a result of the modification of truxene, we can change the electronic structure or create multidimensional materials. Thus, the use of truxenes is very wide.

Wide-range lifetime-tunable and responsive ultralong organic phosphorescent multi-host/guest system

The rational lifetime-tuning strategy of ultralong organic phosphorescence is extraordinarily important but seldom reported. Herein, a series of multi-host/guest ultralong organic phosphorescence materials with dynamic lifetime-tuning properties were reported. By doping a non-room-temperature phosphorescence emitter into various solid host matrices with continuously reduced triplet energy levels, a wide-range lifetime (from 3.9 ms gradually to 376.9 ms) phosphorescence with unchangeable afterglow colors were realized. Further studies revealed that the host matrices were employed to afford rigid environment and proper energy levels to generate and stabilize the long-live triplet excitons. Meanwhile, these multi-host/guest ultralong organic phosphorescence materials also exhibited excitation-dependent phosphorescence and temperature-controlled afterglow on/off switching properties, according to the virtue of various photophysical and thermal properties of the host matrices. This work provides a guiding strategy to realize lifetime-tuning ultralong organic phosphorescence with lifetime-order encoding characteristic towards widespread applications in time-resolved information displaying, higher-level security protection, and dynamic multi-dimensional anti-counterfeiting.

Efficient energy transfer in a tri-chromophoric dyad containing BODIPYs and corrole based on a truxene platform

A star-shaped molecule was designed and synthesized based on a known central truxene platform. Two BODIPY derivatives and one corrole macrocycle were introduced and connected to the 2, 7 and 12-positions of the truxene unit by Suzuki coupling. The dyad was fully characterized by UV-vis absorption, proton nuclear magnetic resonance, mass spectrometry. The direction of energy transfer upon electronic excitation was explored, and the star-shaped molecule system exhibits a highly efficient photoinduced energy transfer process from the excited BODIPY part to the corrole unit.

Tunable luminescence and white light emission of porphyrin-zinc coordination assemblies

Bipodal ligand 5,15-bis(4-carboxyphenyl) porphyrin (H[Formula: see text]DCPP) was designed and synthesized. By adjusting the molar ratio of H[Formula: see text]DCPP, ancillary ligand 4,4-bipyridine (bpy) and zinc acetate salts, three novel coordination assemblies, namely, zero-dimensional dimeric [Zn[Formula: see text](H[Formula: see text]DCPP)[Formula: see text] ·bpy] ·4H[Formula: see text]O ·4DMF (Zn-D), two-dimensional polymeric {[Zn[Formula: see text](DCPP) ·bpy[Formula: see text] ·H[Formula: see text]O ·DMF[Formula: see text]] ·solvent}[Formula: see text] (Zn-2D), and three-dimensional polymeric [Zn[Formula: see text](DCPP) ·bpy[Formula: see text]][Formula: see text] (Zn-3D) were assembled. Due to the delicate integration of multiple chromophores in the coordination space combining bpy, DCPP and MLCT emissions together, photoluminescence (PL) of the three porphyrin-zinc coordination assemblies differ from each other and color tone is tunable from blue to orange with changes of the excitation wavelength. In particular, white light emission (WLE) can be observed by the excitation of 270 to 290 nm, representing the first examples of single component WLE compounds based on porphyrin ligands. Furthermore, temperature-dependent luminescence results in a linear [Formula: see text]–[Formula: see text] relationship in Zn-2D and Zn-3D assemblies, applicable for long wavelength red-emitting thermometers.

Efficient synthesis of 5-oxatruxene and the unusual influence of oxygen heteroatom on its physico-chemical properties

5-Oxatruxene presents new quality among the truxenes. It is a promising compound for the new class of optoelectronic materials.

Synthesis and chemosensory properties of two-arm truxene-functionalized conjugated polyfluorene containing terpyridine moiety

We report the responsive fluorescence chemosensory phenomena of a truxene-functionalized conjugated polymer (P1) with pendant terminal terpyridine (tpy) groups as receptors for metal ions synthesized via a Suzuki polymerization reaction.

Very fast singlet and triplet energy transfers in a tri-chromophoric porphyrin dyad aided by the truxene platform

A trichromophoric dyad composed of an octa-β-alkyl-palladium(II)porphyrin (donor) and two tri-meso-aryl-zinc(II)porphyrins (acceptors) held by a truxene spacer exhibits very fast rates for triplet energy transfers at 77 (kET(T1) = 1.63 × 108 s-1) and 298 K (kET(T1) = 3.44 × 108 s-1), whereas the corresponding singlet energy transfer rates, kET(S1) = 3.9 × 1010 s-1 (77 K) and kET(S1) = 6.0 × 1010 s-1 (298 K), are also considered fast. The interpretation for these results is that the energy transfer processes proceed via a through bond Dexter mechanism (i.e. double electron exchange) supported by comparison with literature data and evidence for a moderate MO coupling between the donor and acceptor chromophores in the frontier MOs.

Truxene: a promising scaffold for future materials

Truxene (10,15-dihydro-5H-diindeno[1,2-a;1′,2′-c]fluorene), which is a heptacyclic polyarene structure, has attracted a great deal of interest due to its exceptional solubility, high thermal stability and ease with which it may be modified.

Origin of the temperature dependence of the rate of singlet energy transfer in a three-component truxene-bridged dyads

We report a truxene-based dyad built upon one donor (tri-meso-phenylzinc(II)porphyrin) and two acceptors (octa-β-alkylporphyrin free base) in which the donor exhibits free rotation around a Ctruxene-Cmeso single bond at 298 K in fluid solution but not at 77 K in a glass matrix, whereas the acceptors have very limited motion as they are blocked by β-methyl groups. This case is interesting because all the structural and spectroscopic parameters affecting the rate for singlet energy transfer according to a Förster Resonance Energy Transfer are only weakly temperature dependent, leaving only the Dexter mechanism explaining the larger variation in rate of energy transfers with the temperature hence providing a circumstantial evidence for a dual mechanism (Föster and Dexter) in truxene-based dyads (or polyads) in the S1 excited states.

Antenna effects in truxene-bridged BODIPY triarylzinc(ii)porphyrin dyads: evidence for a dual Dexter–Förster mechanism

BODIPY uses the truxene bridge to transfer its S₁ energy to the zinc(ii)porphyrin acceptors via a Dexter mechanism almost exclusively.

π-Conjugated Molecules Based on Truxene Cores and Pyrene Substitution: Synthesis and Properties

Two starburst molecules based on pyrene with truxene cores, PYT and PYET, have been designed and synthesised by Pd(0)-catalysed Suzuki coupling and Sonogashira coupling reactions, respectively. Due to the different conjugation length, the solution absorption and emission spectra of PYET in dilute THF were redshifted compared with those of PYT. The solid absorption and emission spectra of PYET were also redshifted. Their thermal decomposition temperatures ( Td) were over 400 °C, and the glass transition temperatures ( Tg) were 96 and 124 °C, respectively, which showed that both materials possess good thermal stability. Electrochemical analysis implied that the HOMOs of PYET and PYT were similar.

Shape-persistent poly-porphyrins assembled by a central truxene: synthesis, structure, and singlet energy transfer behaviors

Four dyad systems composed of a central truxene and either one or three β-substituted zinc(II) porphyrins (ZnP: TruZnP (7) and TruTriZnP (9)) or free-bases (H2P: TruP (6) and TruTriP (8)) have been prepared. The presence of β-methyl groups minimizes π-conjugation through the quasi right angle made by the porphyrin and the truxene planes, and renders these dyads relatively rigid. The position of the absorption and emission 0–0 peaks confirms the role of the truxene and porphyrin as the energy donor and acceptor, respectively. Selective excitation of the truxene results in an efficient singlet energy transfer (S1 ET) from the truxene to the porphyrin unit. The rates for S1 ET (k ET ) are extracted from the change in the fluorescence lifetime of truxene in the presence and absence of the acceptor, and are temperature independent, (TruP (6), TruTriP (8), TruZnP (7) and TruTriZnP (9) are 5.0, 1.4, 1.0 and 1.4 at 298 K and 5.9, 1.3, 2.6, and 0.86 (ns)-1 at 77 K, respectively), consistent with their relative rigidity. These k ET 's are similar to other related but more flexible systems reported by one of us (Inorg. Chem.2011, 50, 11493–11505). The k ET 's time scale was assumed, based on modeling, to be related with hindered rotations about the truxene-porphyrin C–C bonds due to steric hexyl–hexyl interactions. This work confirms this earlier conclusion was correct.