Field-Induced Fluorescence Quenching and Enhancement of Porphyrin Sensitizers on TiO₂ Films and in PMMA Films

Abstract

Three highly efficient porphyrin sensitizersYD2, YD2-oC8, and YD30, either sensitized on TiO 2 films or embedded in PMMA filmswere investigated using electrophotoluminescence (E-PL) spectra. Under both thin-film conditions, on application of an external electric field we observed the quenching of fluorescence of push−pull porphyrins (YD2 and YD2-oC8) and a slightly enhanced fluorescence of the reference porphyrin without an electron donor group (YD30). A nonfluorescent state with charge separation (CS) is proposed to be involved in both YD2 and YD2-oC8 systems so that the electron injection becomes accelerated in the presence of a strong electric field. In contrast, the retardation of the nonradiative process not involving a CS state was the reason for the field-induced enhancement of fluorescence of YD30. The extent of fluorescence quenching of YD2-oC8 was greater than that of YD2 on TiO 2 films, indicating that the ortho-substituted long alkoxyl chains play a key role to accelerate the consecutive electron injection involving the CS state. Our E-PL results indicate that a field-induced variation of fluorescent intensity is related to the efficiency of conversion of solar energy and that further improvement of the performance of devices containing push−pull porphyrin dyes is achievable under an applied electric field.

Stark Spectroscopy of Absorption and Emission of Indoline Sensitizers: A Correlation with the Performance of Photovoltaic Cells

“…Remarkable field-induced quenching of PL of DN488 shows that nonradiative relaxation process­(es) following photoexcitation are enhanced by application of F in DN488. The relaxation process of these dyes which is affected by F may be regarded as the field-induced exciton dissociation which produces a hole and electron pair because a good correlation exists between the photon energy conversion efficiency of the photovoltaic cells constructed with these dyes and the magnitude of the field-induced quenching, as in the case of push–pull porphyrin dyes attached on TiO 2 . In other words, the dye which shows efficient field-induced exciton dissociation is regarded as a dye sensitizer suitable for DSSC.…”

Electric Field Effects on Photoluminescence of CdSe Nanoparticles in a PMMA Film

“…E-PL spectra and E-A spectra were measured by the same system and procedures as reported elsewhere [13][14][15][16][17][18][19][20][21][22]. PMMA (MW = 120,000) was obtained from Aldrich and purified by a precipitation with a mixture of benzene and methanol.…”

“…Measurements of these spectra provide unique information about the differences in electric dipole moment (μ) and molecular polarizability (α) between the ground state and excited states. These spectra have also been used to probe field-induced molecular orientation [19,20], to examine the stability of organic light-emitting diode materials [21], and to examine the efficiency of dye-sensitized solar cells [22].…”

Photoluminescence of P3HT:PCBM bulk heterojunction thin films and effect of external electric field

“…[ 17,25 ] We showed that an external electric field affects the fluorescence intensities of locally excited states of isolated donors or acceptors, and exciplexes, and thereby alters the rates of photoinduced electron transfer of methylene‐linked compounds of phenanthrene and N,N‐dimethylaniline, carbazole and methyl terephthalate, and push‐pull‐type porphyrins in a poly(methyl methacrylate) (PMMA) polymer film. [ 26–30 ] These studies of the effect of an electric field on the fluorescence of push‐pull porphyrins embedded in PMMA and sensitized on TiO 2 revealed that quenching is efficient for sensitized films on TiO 2 because of a rapid injection of electrons into TiO 2 . [ 30 ] Electric‐field effects on the fluorescence of π‐conjugated polymers such as poly[2‐(phenyl)‐3‐(4′‐(3,7‐dimethyloctyloxy)phenyl)‐1,4‐phenylenevinylene‐ co ‐2‐(11′‐decylsulfanylundecanyloxy)‐5‐methoxy‐1,4‐phenylene vinylene] (S3‐PPV) and rr‐P3HT were similarly examined.…”

“…[ 26–30 ] These studies of the effect of an electric field on the fluorescence of push‐pull porphyrins embedded in PMMA and sensitized on TiO 2 revealed that quenching is efficient for sensitized films on TiO 2 because of a rapid injection of electrons into TiO 2 . [ 30 ] Electric‐field effects on the fluorescence of π‐conjugated polymers such as poly[2‐(phenyl)‐3‐(4′‐(3,7‐dimethyloctyloxy)phenyl)‐1,4‐phenylenevinylene‐ co ‐2‐(11′‐decylsulfanylundecanyloxy)‐5‐methoxy‐1,4‐phenylene vinylene] (S3‐PPV) and rr‐P3HT were similarly examined. [ 31–34 ] Upon application of an electric field S3‐PPV showed an enhanced or quenched PL dependent on the excitation wavelength.…”