A bacteriochlorophyll derivative of the formula II: ** Formula ** wherein M represents 2H, a divalent metal atom selected from Pd, Pt, Co, Sn, Ni, Cu, Zn or Mn, or a selected trivalent metal atom among the group consisting of Fe, Mn, Co, Au, Al, Gd, Er, Yb and Cr； each R1, R'2 and R6 is independently Y-R8, -NR9R'9 or -N + R9R'9R "9A； Y is O or S； R4 is -CH>； = CR9R'9, -CH>； = CR9Hal, -CH>； = CH-CH2-NR9R'9, -CH>； = CH-CH2- N + R9R'9R "9A -, - CHO, -CH>； = NR9, - CH>； = N + R9R'9A-, - CH2-OR9, -CH2-SR9, -CH2-Hal, -CH2-R9, -CH2-NR9R'9, -CH2-N + R9R'9R "9A-, -CH2-CH2R9, -CH2- CH2Hal, -CH2 -CH2OR9, -CH2-CH2SR9, -CH2-CH2-NR9R'9, -CH2-CH2-N + R9R'9R "9A-, -COCH3, C (CH3)>； = CR9R'9, - C (CH3)>； = CR9Hal, -C (CH3)>； = NR9, -CH (CH3)>； = N + R9R'9A-, -CH (CH3) -Hal, -CH (CH3) -OR9, -CH (CH3) -SR9, -CH (CH3) - NR9R'9, -CH (CH3) -N + R9R'9R9A- or -C≡CR9； R8, R9, R'9 and R "9 each independently is: (a) H； (b) C1-C25 hydrocarbyl； (c) C1-C25 hydrocarbyl, preferably C1-C25 alkyl, more preferably C1-C10 alkyl or C1-C6, substituted with one or more functional groups selected from halogen, nitro, oxo, OR, SR, epoxy, epitium, aziridine, -CONRR ', -COR, COOR, -COSR, -OSO3R, -SO3R -SO2R, - NHSO2R, -SO2NRR ', -NRR',>； = N-OR,>； = N-NRR ', -C (>； = NR) -NR'R ", -NR-NR'R", - (R) NC ( >； = NR) -NR'R ", O ← NR-,>； C>； = NR, - (CH2) n-NR-COR ', - (CH2) nCO-NRR', -O- (CH2) n-OR , -O- (CH2) nO- (CH2) nR, - OPO3RR '-PO2HR, -PO3RR' or -, where n is an integer from 1 to 6, each R and R 'and R "is independently H, hydrocarbyl or heterocyclyl or two of R, R 'and R ", together with the N atom to which they are attached, form a 3-7 membered saturated ring, optionally containing one or more heteroatoms selected from O, S or N and is optionally further substituted on the additional N atom with alkyl optionally substituted with halogen, hydr oxyl or amino； (d) C1-C25 hydrocarbyl, preferably C1-C25 alkyl, more preferably C1-C10 or C1-C6 alkyl, substituted with one or more f
