Twenty-fold Enhancement of Gadolinium-Porphyrin Phosphorescence at Room Temperature by Free Gadolinium Ion in Liquid Phase

Abstract

The influence of free gadolinium ion (Gd3+) on room-temperature phosphorescence (RTP) of gadolinium labeled hematoporphyrin monomethyl ether (Gd-HMME) was studied. Twenty-fold enhancement of Gd-HMME RTP by the titration of free Gd3+ was achieved. We found that the absorption from the ground (S 0) to singlet excited states of Gd-HMME did not change with the addition of Gd3+, which means that the phosphorescence quantum yield has been tuned from 1.4% to 28%. According to the excitation spectra, the transition possibility from S0 to the lowest triplet excited state (T1) is increased by 1.2-fold because of the heavy atom effect of free Gd3+. The phosphorescence lifetime of Gd-HMME with free Gd3+ is 7.0-fold greater than that of Gd-HMME itself, which demonstrates that the nonradiative processes of Gd-HMME is decreased by Gd3+ with the rate constant of nonradiative processes decreasing from 2.2(2) × 105 to 2.8(2) × 104 s–1. This sharp decrease is mainly responsible for the huge enhancement of Gd-HMME RTP. The reason for the decrease of nonradiative processes is due to the formation of a rigid microenvironment, which protects Gd-HMME from being quenched.

Covalent Synthesis of Two Hybrids Composed of Dawson-Type Polyoxometalate and Porphyrin with Remarkable Third-Order Optical Nonlinearities Reflecting the Effect of Polyoxometalates

“…It is well-known that porphyrins possess very strong excited state absorption from both the triplet as well as the singlet states, singlet excited state has a shorter lifetime and transfers the excited state energy to triplet state through inter system crossing (ISC) . Porphyrin molecules typically emit in the 600–700 nm range due to radiative relaxation. , However, after attachment of POM on porphyrin molecules, energy difference of singlet and triplet excited states of hybrids 1 and 2 are very small which speed up the ISC process, ,, consequently enhance the optical nonlinearities of the resulting hybrids , while the luminescence is quenched by rapid photo induced electron transfer from triplet excited state porphyrin molecules to Dawson POMs (Figure ).…”

“…41 Porphyrin molecules typically emit in the 600−700 nm range due to radiative relaxation. 84,85 However, after attachment of POM on porphyrin molecules, energy difference of singlet and triplet excited states of hybrids 1 and 2 are very small which speed up the ISC process, 41,86,87 consequently enhance the optical nonlinearities of the resulting hybrids 86,88 while the luminescence is quenched by rapid photo induced electron transfer from triplet excited state porphyrin molecules to Dawson POMs (Figure 9).…”

Intrinsic Characterization Method on the Heavy Atom Effect of Metalloporphyrins

“…The room temperature phosphorescence in porphyrins is always absent as the forbidden transition from the excited triplet state (T 1 ) to the ground state (S 0 ). − The decoration of porphyrin rings by heavy metal ions can break this forbidden process, which is known as the heavy atom effect (HAE). − Conventionally, the intensity and lifetime of phosphorescence had been employed to evaluate the functionality of the HAE. For instance, Shi et al reported that the phosphorescence quantum yield (Φ P ) of PDBCz is 15 times higher than its parent compound PDCz once the bonds of halogen Br ions and porphyrin rings are introduced .…”

A first principles examination of phosphorescence

“…The most well known and efficient phosphorescent compounds are in the organometallic family of chromophores, such as metal suldes or metal-cored porphyrins. 15,20,[25][26][27][28][29][30] However, fabrication of these kinds of molecules is neither cheap nor environmentally sound. The design of bio-friendly organic compounds for phosphorescent applications which are not limited by temperature or open-air is extremely difficult as the coupling between singlet and triplet excited states is typically quite weak.…”