Ultraviolet Light Detectable Circularly Polarized Room Temperature Phosphorescence in Chiral Naphthalimide Self-Assemblies
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The combination of circularly polarized luminescence (CPL) and pure-organic room temperature phosphorescence (RTP) potentially facilitates the construction of organic chiroptical optoelectronics and display materials, which however are challenging to use in realizing smart control of luminescent colors and switchable chiroptical properties. Here, we show a host-guest strategy to fabricate color-tunable RTP-based circularly polarized phosphorescence. Napthalimides were conjugated directly to chiral segments, of which supramolecular chirality and CPL activities in solid-states could be triggered by substituting bromine atoms on amines. Introducing tetracyanobenzene as an achiral host matrix via simple grinding would allow for the intersystem crossing to trigger red RTP and corresponding CPL by excitation lower than 320 nm, with a large Stokes shift more than 300 nm. The critical excitation wavelength of the RTP switch is determined by the absorbance of tetracyanobenzene. When the excitation wavelength was larger than 320 nm, blue fluorescence dominated with turned off RTP and CPL. The excitation wavelength-dependent RTP and CPL switch allows for detecting ultraviolet (UV) light, showing distinguishable red-blue luminescent color transition, accompanied by on/off RTP. Changing the host matrix from tetracyanobenzene to tricyanobenzene or dicyanobenzene could adjust the critical detecting wavelength limit from 320 to 300 nm. This work establishes a strategy to realize color-tunable, UV light detectable RTP and CPL under smart control.Keywords:
Intersystem crossing
Ultraviolet
Abstract The traditional method to achieve ultralong organic phosphorescence (UOP) is to hybrid nπ* and ππ* configurations in appropriate proportion, which are contradictory to each other for improving efficiency and lifetime of phosphorescence. In this work, through replacing the electron‐donating aromatic group with a methoxy group and combining intramolecular halogen bond to promote intersystem crossing and suppress non‐radiative transition, an efficient UOP molecule (2Br‐OSPh) has been synthesized with the longest lifetime and brightest UOP among its isomers. As compared to CzS2Br, which has a similar substituted position of bromine atom and a larger k isc (the rate of intersystem crossing), the smaller Δ E TT* (the energy gap between monomeric phosphorescence and aggregated state phosphorescence) in 2Br‐OSPh could accelerate the transition from T 1 to T 1 *. This research indicates that both generation and accumulation of triplet excitons play an important role in realizing efficient UOP materials.
Intersystem crossing
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Intersystem crossing
Terbium
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In the past decade, halogen bonding (XB) has been utilized extensively in the design of novel materials and new drugs. One of the emerging applications of XB is in devising organic room-temperature phosphorescent materials. Several reports showed that the use of benzaldehyde-based phosphors with appropriate XB donors results in high phosphorescence quantum yields because of enhanced intersystem crossing (kISC) and phosphorescence (kPH) rates. It is often advocated that a combination of factors, namely, rigidification, heavy-atom effect, and reduction of quenching by triplet dioxygen, is responsible for the enhancement. However, to what extent each factor contributes to the enhancement is unknown. In this study, we performed ab initio excited-state calculations on two XB complexes, benzaldehyde···XF (X = Br and I), with varying XB distance to elucidate the effect of XB on kISC and kPH. Our results show that XB reduces the kISC of benzaldehyde and changes the character of T₁ from which phosphorescence takes place. Hence, the generally accepted assumption that XB enhances spin–orbit coupling and kISC is oversimplified.
Intersystem crossing
Benzaldehyde
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Intersystem crossing
Thermalisation
Picosecond
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The fluorescence and phosphorescence emission spectra and the phosphorescence lifetime of benzene in a rigid solution at 77°K have been measured as a function of concentration and excitation wavelength. The shape of the emission spectra is independent of concentration. The internal conversion efficiency βλ between higher excited states and the lowest excited singlet state is dependent on, excitation wavelength and concentration. The action spectra of fluorescence and phosphorescence are identical for all concentrations, except in pure benzene for which no phosphorescence was detected. The behaviour of βλ as a function of wavelength of excitation cannot be explained by an intersystem crossing process between higher singlet excited states and the triplet manifold. The decrease in phosphorescence with increase in concentration, which is accompanied by an increase in fluorescence, is attributed to a decrease not only of the phosphorescence lifetime, but also of the rate of intersystem crossing between the lowest excited singlet state and the triplet manifold. No delayed fluorescence was detectable.
Intersystem crossing
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In the past decade, halogen bonding (XB) has been utilized extensively in the design of novel materials and new drugs. One of the emerging applications of XB is in devising organic room-temperature phosphorescent materials. Several reports showed that the use of benzaldehyde-based phosphors with appropriate XB donors results in high phosphorescence quantum yields because of enhanced intersystem crossing (kISC) and phosphorescence (kPH) rates. It is often advocated that a combination of factors, namely, rigidification, heavy-atom effect, and reduction of quenching by triplet dioxygen, is responsible for the enhancement. However, to what extent each factor contributes to the enhancement is unknown. In this study, we performed ab initio excited-state calculations on two XB complexes, benzaldehyde···XF (X = Br and I), with varying XB distance to elucidate the effect of XB on kISC and kPH. Our results show that XB reduces the kISC of benzaldehyde and changes the character of T1 from which phosphorescence takes place. Hence, the generally accepted assumption that XB enhances spin–orbit coupling and kISC is oversimplified.
Intersystem crossing
Benzaldehyde
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Gas-phase phosphorescence spectra of naphthalene-h8 and -d8 are reported. A triplet lifetime of 4.2 msec was derived from the 000 band of the n-h8 phosphorescence. Intersystem crossing yields of single vibronic levels in S1 were determined from excitation spectra of biacetyl phosphorescence.
Intersystem crossing
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The traditional method to achieve ultralong organic phosphorescence (UOP) is to hybrid nπ* and ππ* configurations in appropriate proportion, which are contradictory to each other for improving efficiency and lifetime of phosphorescence. In this work, through replacing the electron-donating aromatic group with a methoxy group and combining intramolecular halogen bond to promote intersystem crossing and suppress non-radiative transition, an efficient UOP molecule (2Br-OSPh) has been synthesized with the longest lifetime and brightest UOP among its isomers. As compared to CzS2Br, which has a similar substituted position of bromine atom and a larger kisc (the rate of intersystem crossing), the smaller ΔETT* (the energy gap between monomeric phosphorescence and aggregated state phosphorescence) in 2Br-OSPh could accelerate the transition from T1 to T1 *. This research indicates that both generation and accumulation of triplet excitons play an important role in realizing efficient UOP materials.
Intersystem crossing
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The phosphorescence spectra, mean lifetimes of phosphorescence and ratios of phosphorescence/ fluorescence quantum yields have been measured for 5-phenyltetrazole and its three methyl derivatives in a polyvinyl alcohol film over the temperature range of (77-250) K. Temperature responses of the non-radiative intersystem crossing constant. K ST , and the non-radiative triplet state deactivation constant, k m , have been investigated on the basis of these measurements. The energy of activation for the non-radiative transitions has been determined. With the methyl 5-phenyltetrazoles, the thermal deactivation of the triplet state, contrary to the intersystem crossing, has been found to be influenced by the position of the methyl substituent in the phenyl ring.
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